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WATER MANAGEMENT ALTERNATIVES FOR STRAWBERRY TRANSPLANT ESTABLISHMENT AND FREEZE PROTECTION IN FLORIDA

By

IXCHEL M. HERNANDEZ-OCHOA

A THESIS PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2013

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© 2013 Ixchel Manuela Hernandez Ochoa

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To my family and friends who stay with me through the whole process giving me their support, and to my advisor for his lessons and patience.

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ACKNOWLEDGMENTS

Thanks to my family, especially to my mom, Maria Luisa, my sister Nina, and my

Uncle Rene, for their support and for being with me through the whole process, to my

friends for being there supporting me, helping me and making me laugh. Also thanks to

my committee members Dr. Xin Zhao and Dr. Craig Stanley for their advice and

especially to my advisor Dr. Santos, for all his lessons and patience.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS .................................................................................................. 4

LIST OF TABLES ............................................................................................................ 6

ABSTRACT ..................................................................................................................... 7

CHAPTER

1 INTRODUCTION ....................................................................................................... 9

2 LITERATURE REVIEW ........................................................................................... 13

Cultivar Description ................................................................................................. 15 Water Use for Strawberry Production in Florida ...................................................... 16 Chilling and Freezing Injury .................................................................................... 17 Establishment and Freeze Protection Methods ...................................................... 19

Sprinkler Irrigation ............................................................................................ 19 Row Covers ...................................................................................................... 21 Crop Protectants .............................................................................................. 23

3 COMPARISON OF FOLIAR AND ROOT-DIPPED CROP PROTECTANTS FOR STRAWBERRY TRANSPLANT ESTABLISHMENT ............................................... 27

Overview ................................................................................................................. 27 Materials and Methods............................................................................................ 28 Results and Discussion........................................................................................... 30

Foliar Crop Protectant Study ............................................................................ 30 Root-Dipped Crop Protectants Study ............................................................... 32

4 COMPARISON OF FREEZE PROTECTION METHODS FOR STRAWBERRY PRODUCTION ........................................................................................................ 39

Overview ................................................................................................................. 39 Materials and Methods............................................................................................ 40 Results and Discussion........................................................................................... 41

2011-2012 Season ........................................................................................... 41 2012-2013 Season ........................................................................................... 43

5 CONCLUSIONS ...................................................................................................... 55

LIST OF REFERENCES ............................................................................................... 58

BIOGRAPHICAL SKETCH ............................................................................................ 66

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LIST OF TABLES

Table page 3-1 Climate conditions from October 12 to October to October 26 2012, in Balm,

Fl. ....................................................................................................................... 36

3-2 Effects of foliar crop protectants on plant diameter, and total early fruit number and weight of bare-root strawberry transplants, 2012-13. Balm, FL. ..... 37

3-3 Effects of root-dipped crop protectants in plant diameter and total early fruit number and weight of strawberry transplants, 2012-13, Balm, FL...................... 38

4-1 Environmental conditions from October 2011 to March 2012. Balm, Florida. ..... 47

4-2 Effects of freeze protection methods on plant number and plant growth, Balm, FL, 2011-12. ....................................................................................................... 48

4-3 Effects of freeze protection methods on the minimum seasonal air temperatures in each treatment, water use, and early and total markefruit weight and number, Balm, FL, 2011-12. ............................................................. 49

4-4 Effect of freeze protection methods on the minimum seasonal temperature for each treatment, and the first six harvests after a freezing event on strawberry markefruit weight and number, Balm, FL, 2011-12. ............................................ 50

4-5 Environmental conditions from October 2012 to March 2013. Balm, Florida. ..... 51

4-6 Effects of freeze protection methods on plant number and plant growth, Balm, FL, 2012-13. ....................................................................................................... 52

4-7 Effects of freeze protection methods on the minimum seasonal air temperatures in each treatment, water use, and early and total markefruit weight and number, Balm, FL, 2012-13. ............................................................. 53

4-8 Effect of freeze protection methods on the minimum seasonal temperature for each treatment, and the first six harvest after a freezing event on strawberry marketable fruit weight and number, Balm, FL, 2012-13. ................................... 54

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

WATER MANAGEMENT ALTERNATIVES FOR STRAWBERRY TRANSPLANT

ESTABLISHMENT AND FREEZE PROTECTION IN FLORIDA

By

Ixchel M. Hernandez-Ochoa

December 2013

Chair: Bielinski Santos Major: Horticultural Sciences

Florida is the second largest strawberry (Fragaria × ananassa) producer in the

U.S. Production fields are concentrated in Plant City and Dover in west-central Florida.

Water resources in this area are shared between agriculture and urbanization. During

strawberry establishment and freeze protection, the standard practice is using sprinkler

irrigation (i.e. 17 L m-1), which is inefficient due to the use of large volumes of water.

Several alternatives to reduce water usage during these phases were identified (i.e.

reduced-volume sprinklers, row covers, and crop protectants). The overall goal of this

study is to evaluate and compare the effects of different transplant establishment and

freeze protection methods on water savings, growth and yield of strawberry. Foliar and

root-dipped crop protectants were evaluated in two separate trials. In addition, the effect

of freeze protection alternatives (i.e. reduced-volume sprinklers, light and heavy row

covers, and a crop protectant) were also assessed.

In the crop protectant trials for transplant establishment, early marketable fruit

weight and number was the same when using crop protectant applications as 10 days

of sprinkler irrigation (DSI) in both trials. When using 7 DSI alone resulted in decrease

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on early marketable yield in both trials. Sprinkler-irrigated treatments showed lower

plant diameter than crop protectant treatments. For the freeze protection study, there

was no difference in early and total marketable yield among treatments when minimum

temperature was (-3oC), temperature inside row covers was between 2 and 8oC higher

the temperature outside. No difference among treatments in plant diameter was

observed.

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CHAPTER 1 INTRODUCTION

The cultivated strawberry (Fragaria × ananassa Duch.) is a perennial woody

plant that belongs to the Rosaseae family. This commercially-grown plant is a hybrid

derived from the cross between F. chiloensis and F. virginiana. The primary structure is

the crown from which leaves, runners, roots, axillary crowns, and inflorescences grow

(Darnell, 2003). The berry develops from the flower receptacle: a fleshy pith surrounded

by a ring of vascular bundles with branches ending in the aquenes, which is the real fruit

(Darrow, 1966).

The U.S. occupies the first place among strawberry producers around the world

with 23,060 harvested ha and nearly 1.3 million t of fruit during 2011 (USDA, 2012;

FAO, 2011). About 83% of the strawberry production in the U.S. is concentrated in two

states: California and Florida with 15,378 and 4,000 ha, respectively (USDA, 2012).

During the winter season, Florida supplies the majority of the fresh market for the

country (Boriss et al., 2012). Almost 95% of the production fields are located in the

west-central area of Hillsborough and Manatee Counties (Mossler, 2010).

Strawberries are planted from late September to mid-October, and the harvest

period occurs from early December through early April (Hochmuth et al., 1993). During

strawberry establishment and freeze protection, the standard practice is the use of

overhead sprinklers delivering water at about 17 L m-1. Bare-root transplants brought

from Canadian nurseries are set into fumigated, black polyethylene mulched beds in

environments with high temperatures and evapotranspiration. Sprinkler irrigation is used

from 8 to 12 h day-1 during the first 10 days to provide a microclimate that reduces

temperature around crowns and promotes new root growth (Hochmuth et al., 2006;

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Santos et al., 2012). This activity consumes about 4940 m3 ha-1 of water, which is about

one-third of the total water use during the season (Albregts and Howard, 1985).

During the season, strawberries are subjected from four to six freezing nights.

Sprinkler irrigation uses about 514 m3 ha-1 per freezing night (Santos et al., 2011a).

During the unusual winter of 2010, around 11 freezing nights occurred and large

volumes of water were pumped to protect the crop. As a result of these freezing nights,

the aquifer level dropped 18 m allegedly causing 750 residential dried wells and more

than 140 sinkholes in the area. This phenomenon has occurred three times over the last

ten years. After the last period of freezing nights in 2010 and 2011, the Southwest

Florida Water Management District began working on trying to implement a water

management plan to protect the aquifers. The Plant City-Dover area was declared a

water use caution area, causing special rules for water use during freeze protection to

be developed (SWFWMD, 2011).

The use of sprinkler irrigation for transplant establishment and freeze protection

are highly inefficient due to the use of large volumes of water, most of which ends

running off to the drainage canals, leaching nutrients from the root zone or lowering

aquifer level. During freeze protection, sprinkler irrigation may result in injury to green

and ripe fruit due to the high impact of water droplets (Bish et al., 1997; Domoto, 2006;

Hochmuth et al., 1986; Jackson and Parsons, 1994; Perry, 1998; Poling et al., 1991).

Reduced-volume sprinklers, row covers, and crop protectants could be alternatives to

sprinkler irrigation. However, more research is needed to assess the effect of these

techniques on strawberry growth and yield. In general, sprinklers are set for the worst

scenarios and deliver more water than is needed for crop protection and growth (Fisher

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and Shortt, 2009; Perry, 1998). Reduced-volume sprinklers might be a suitable option to

decrease volumes of water used during transplant establishment and freeze protection.

Crop protectants are products designed to reduce environmental stress. During

transplant establishment, these products can be used either as foliar or root-dipped

applications. Foliar products are based on natural-occurring materials like calcium

carbonate, kaolin clay or aluminum silicate. When the product is applied on plant

canopies, it creates a coat that reflects radiation, reducing transpiration, and water

stress on transplants. Moreover, root-dipped crop protectants concentrate water around

the plant crown to provide enough moisture and increase water availability for the new

roots (Hodges et al., 2006). Crop protectants for freeze protection are usually composed

of polymeric terpenes that help decreasing the freezing point on plant tissues, thus

preventing or reducing freezing damage on plants (Perry, 1998).

Row covers are flexible, transparent or semi-transparent blankets made up of

polyethylene, polypropylene, polyester, and other materials. They are commonly used

to enhance crop growth and yield by increasing temperature around the plants during

cold periods and also acting as barriers for pests (Hochmuth et al., 1987; Nair and

Ngouajio, 2010; Stall et al., 1985). Row covers help in decreasing the influence of wind,

evaporative and radiational cooling, and convection by keeping high temperatures for

longer periods of time. The overall goal of this study was to determine the effectiveness

of water-saving strategies during strawberry transplant establishment and freeze

protection.

The specific objectives were:

Determine the effects of using crop protectants on strawberry transplant establishment growth and early marketable yield.

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Compare the effects of reduced-volume sprinkler and non-irrigation alternatives for freeze protection on water savings, strawberry growth, and early and total marketable yield.

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CHAPTER 2 LITERATURE REVIEW

Strawberry is one of the most high-value fruit crops in the U.S. with 1.3 million t

harvested and $2.4 billion in gross sales during the 2011 season (USDA, 2012). The

main market window for Florida strawberry is during winter months when California

production is out of the market. Most of the strawberry crop produced in the state is

utilized for fresh consumption. Strawberries produced nowadays are a cross between F.

chiloensis and F. virginiana. Both of these species have their heritage in America. F.

chiloensis was first identified in the coastal areas of Chile and it was brought and

domesticated in France during the 18th century. F. virginiana is also an eastern north

American species that was introduced to France during the 1600’s (Darrow, 1966). After

their cross in Europe, the hybrid was re-introduced to America during the 19th century.

Strawberries are grown in moderate climates with temperatures around 20oC and low

humidity conditions (Boriss et al., 2012; Rowley et al., 2010). In Florida, strawberries are

commonly-grown in soil under hill plasticulture system (Cantliffe et al., 2007; Chandler

et al., 2000). During early October, bare-root transplants are set into fumigated

polyethylene-mulched beds and harvested from early December to late March

(Hochmuth et al., 1993).

There is a broad range of genetic variation among strawberry species. The

commercially-grown hybrid plant is an octoploid, 2n = 8 (Darrow, 1966). This

heterogozity makes it hard to breed (Nyman and Wallin, 1992). The plant basic

structure is the crown, which is a compressed stem from where shoots and roots

develop (Darnell, 2003). The trifoliated leaves grow surrounding the crown and elongate

until they are fully expanded. The axillary leaf buds may become axillary crowns or

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runners, depending on the stage of the plant and the environmental conditions (Darnell,

2003). Each axillary crown has its own inflorescence (Poling, 2012). Runners are

daughter plants, which are vegetative organs that grow with identical characteristics to

the mother plant. Runners are the most common method for crop propagation (Bish et

al., 1997). The root system in strawberries is adventitious. In sandy soils, they can

penetrate 30 cm deep, but most of the roots are concentrated in the first 15 cm of soil

(Dana, 1980; Darrow 1966).

Flower induction in strawberry is influenced by the combination of two main

factors: photoperiod and temperature. There are three main types of cultivated

strawberries, which are divided depending on the flowering pattern in day-neutral, short-

day or June-bearing, and ever-bearing cultivars. Flowering in day-neutral cultivars is

determined mostly by changes in temperature, while flowering in ever-bearing and

June-bearing cultivars is influenced mainly by changes in photoperiod (Darnell, 2003;

Taylor, 2000). Ever-bearing cultivars produce flowers during long-day conditions, while

June-bearing cultivars flower during fall when days are less than 14 h of light. Low

temperatures also increase flower bud initiation (Darnell, 2003). After flower induction,

apical meristems start to differentiate into flower buds. Flower buds are arranged into

inflorescences with a primary flower, which will develop into the largest fruit, and the

secondary and tertiary flowers into smaller fruit (Darnell, 2003; Taylor, 2002). The

strawberry flower is perfect with 10 sepals, around five petals, 20 stamens, 60 to 600

pistils depending on the flower. Flower pollination is mostly by wind and insects

(Darnell, 2003). The real seeds are pollinated pistils that remain attached to the

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receptacle surface during its expansion, resulting in an accessory fruit or aggregate

(Darnell, 2003; Poling, 2012).

Cultivar Description

‘Strawberry Festival’ is a short-day cultivar released by the University of Florida

(UF) in 2000. It was the predominant variety in Florida west-central area during the

2009-10 season with approximately 60% of the total planted area (Chandler et al., 2009;

Whitaker et al., 2011). This variety was a result of the cross between ‘Rosa Linda’ and

‘Oso Grande’ (Chandler et al., 2000). ‘Rosa Linda’ is a variety released by UF in 1996,

this variety was chosen due to its high early yield and fruit shape, and ‘Oso Grande’,

which is an University of California variety was selected for its fruit quality (Chandler et

al., 2000). ‘Strawberry Festival’ fruit is medium size with conic shape and deep red

color, firmness, and resistant skin to external damage that makes it excellent for

shipping. The upright growth of leaves makes it easy to harvest (Chandler et al., 2000;

Whitaker et al., 2012).

‘Florida Radiance’ was released by UF in 2009 as a result of the cross between

‘Winter Dawn’ and ‘FL 99-35’. ‘Winter Dawn’ was a variety selected for its high early

yield and large fruit shape. ‘FL 99-35’ was chosen for its desirable characteristics such

as firm and attractive fruit (Chandler et al., 2009). This variety ranked in second place

with 15% of the total planted acreage in 2010-11 season (Whitaker et al., 2012). Its fruit

is medium conic in shape and produce elongated fruit during early yield. Fruit color

depends on the stage of ripening from glossy bright to dark red (Chandler et al., 2009).

Plant growth habit is more open with elongated pedicels compared to ‘Strawberry

Festival’ (Chandler et al., 2009).

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According to Santos et al., (2009), ‘Strawberry Festival’ had the highest early and

total fruit number during both seasons among other cultivars such as ‘Winter Dawn’,

‘Florida Elyana’, ‘Florida Radiance’, ‘Ruby Gem’, and ‘Treasure’. However, during early

season and in late February, yields were reduced due to smaller fruit size (Chandler et

al., 2009). ‘Florida Radiance’ complements this fruit reduction during that period with

high yield and consistent fruit shape throughout the season (Chandler et al., 2009;

Santos et al., 2009; Whitaker et al., 2012). ‘Strawberry Festival’ is intermediate

susceptible to anthracnose fruit rot caused by Colletotrichum acutatum, and less

susceptible than ‘Sweet Charlie’ to botrytis fruit rot caused by Botrytis cinerea (Chandler

et al., 2000, 2004). ‘Florida Radiance’ is moderately resistant to both of these diseases,

which are the two most important fruit diseases during cultivation (Mackenzie et al.,

2006).

Water Use for Strawberry Production in Florida

Water availability and quality play important roles in urbanization development.

Primary water withdrawal uses in Florida are for public and agricultural consumption,

accounting for 80% of the total use. Fresh water withdrawals in Florida during 2010

were approximately 24.6 million m3 day-1. About 65% of total water withdrawals come

from surface water sources, which is the most important water source (United States

Geological Service, 2010). It is estimated that population growth in Florida from 2005 to

2025 will be up one third, which means an increase in water withdrawals demand of

≈40% (Florida Department of Environmental Protection, 2010). Sustainability for water

management is important from an environmental point of view. The mean to reduce the

amount of water used for agriculture is to identify agricultural practices that use major

amounts of water and focus on them to offer practical and sustainable alternatives.

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In Plant City and Dover, Hillsborough County, water resources are also shared

between agricultural and urban uses (Hochmuth et al., 2006; Santos et al., 2011a,

2012). Special rules for water use in agriculture were implemented since 2010, when

unusual winters took place and high amounts of water were applied to protect the crop

from freezing damage. This activity allegedly caused a drop in the Floridian aquifer level

of 18 m. It is unclear whether as a result of these events, about 140 sinkholes and more

than 750 dried wells occurred in the area (Aurit et al., 2013; Southwest Florida

Management District, 2011). However, public pressure has suggested there is a link

between both events. Consequently, there is a need to reduce the amount of water

used for strawberry production, particularly during transplant establishment and freeze

protection. The common practice in both activities is the use of sprinkler irrigation, which

uses about two-thirds of the total amount of water utilized during the season (Hochmuth

et al., 2006). The quantity of water used with sprinkler irrigation during transplant

establishment is approximately 4940 m3 ha-1, and during freeze protection, around 556

m3/ha of water per night are used to protect the crop (Hochmuth et al., 1993 and 2006;

Santos et al., 2011a and 2012).

Chilling and Freezing Injury

When plants are exposed to low temperatures, they are subject to two types of

injury: chilling injury and freezing injury. Chilling injury happens in relative sensible

crops, such as tropical and subtropical fruits. Damage occurs when plants are exposed

to temperatures between 10 and 15oC, but above 0oC, which is the freezing point for

water (Wang, 1990). Decrease in temperature has a direct effect on lowering cell

metabolism. Under prolonged conditions tissue damage, such as discoloration, surface

damage, and interruption in plant growth and ripening process may occur (Wang, 1990;

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Wang and Wallace, 2004). When plants are subjected to temperatures below 0oC,

freezing injury occurs causing disruption of cell walls due to ice crystal formation

(Lindow, 1983). Populations of ice-nucleation active bacteria act as centers to initiate

ice formation (Lindow, 1983). A decrease on the population of ice-nucleation bacteria

causes a decrease on the freezing point of water, this process is called super cooling.

Solute concentration and rate of temperature drop also have an influence on ice crystal

formation (Wang, 1990). The amount of solutes dissolved in water decreases freezing

point. Water in apoplastic spaces has less solute concentration and freezes first, then

water moves from the intracellular space to apoplastic space by differences in water

potential, causing dehydration. Under natural conditions, temperature drops at low rates

and then ice crystals are bigger causing cell membrane breaking. However, when ice

formation occurs fast, ice crystals are small and the freezing damage is significantly low.

Plant acclimatation to cold temperatures is called hardening, which is an increase

in solute concentration in plant tissue or a decrease in ice-nucleation bacteria or both

processes happening at the same time (wang, 1990). Another mechanism developed by

the exposure to low temperatures is antifreeze protein formation. Their function is to

reduce the speed of ice formation by attaching to the crystals surface (Wang, 1992).

Gene expression also plays a role by promoting biochemical changes, such as abscisic

acid production, which might be a main factor in developing plant response to

acclimation (Campalans et al., 1999; Tomashow, 1994). In order to prevent or reduce

freeze damage many techniques have been developed. Most of them are based on

either add or hold the temperature in the surrounding air to keep plant tissues at higher

temperature than freezing point (Perry, 1998), Other techniques such as

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cryoprotectants aim to prevent ice formation by reducing population of active ice-

nucleation bacteria on plant tissues (Hew and Yang, 1992). Critical temperatures for

freezing injury in strawberry will depend on the plant organs. The most susceptible to

freezing injury are the open blossoms at -1.1oC, followed by fruit at -2.2oC. Early stages

are less susceptible to low temperatures, tight bud and popcorn stage suffer damage at

-3 and -5.5oC, respectively (Perry and Poling, 1986).

Establishment and Freeze Protection Methods

Sprinkler Irrigation

Water has been used for a long time to protect strawberries during transplant

establishment and freeze protection. The physical phenomenon behind this method is

based on how water absorbs and releases energy, when it changes from one physical

state to another. A calorie is described as the quantity of heat needed to raise in 1°C the

temperature of 1 g of water at 1 atm. During transplant establishment, water is applied

to provide an appropriate microclimate to cool crowns and promote root and shoot

growth. Cooling occurs when water changes from liquid to vapor. In this process water

absorbs approximately 540 calories from the surrounding air and it is called evaporative

cooling. This occurs due to the difference between air and saturated vapor pressures.

As long as the air vapor pressure, which is a measure of the water vapor in the air, is

less than the saturated vapor pressure, the process continues occurring. In addition,

when the temperature of applied water is lower than the temperature outside, water

absorbs heat due to the temperature gradient and also helps to decrease the

temperature (Albregts and Howard, 1985).

A similar principle is applied when water is used for freeze protection. Under

freezing conditions, applied water turns from liquid to ice releasing energy. For each 1 g

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of water turning to ice, approximately 80 calories are released, supplying heat to keep

plant tissues near or above 0°C. This process is called latent heat of fusion. At the same

time, evaporative cooling occurs, which absorbs approximately 540 calories. This is

nearly 7 times from what it is being released by latent heat of fusion. Therefore, it

becomes necessary to apply 7 times the volume of water needed in order to keep a

balance between the energy released by latent heat of fusion, and the energy absorbed

by evaporative cooling. Otherwise, the effect will be the opposite thus damaging the

crop (Perry, 1998).

Environmental factors such as wind speed, dew point, and relative humidity

affect appropriate application and distribution of water. Under conditions where wind

speeds are above 8 km h-1, the water volume needed to get effective protection is three

to four times more than in calm conditions, because latent heat will be removed and

uniformity of application will be compromised (Perry, 1998; Powell and Himelrick, 2000).

Dew point is the temperature at which air becomes saturated with water vapor and

condenses forming dew on surfaces. It depends on the relative humidity, since the drier

the air, the lower the dew point (Perry, 2001). When dew point is low, sprinkler irrigation

needs to be turned on before the temperature in the air decreases 1°C. When sprinkler

irrigation is applied under dry conditions, evaporative cooling will be favored instead of

latent heat of fusion, causing an opposite effect of temperature decrease (Fisher and

Shortt, 2009).

Most of the strawberry production fields are equipped with sprinklers delivering

17 L m-1, which is equivalent to 155 m3 ha-1 of water per h, being enough to maintain

and protect the crop during the season. This type of sprinkler is used for both strawberry

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transplant establishment and freeze protection. The amount of water used during freeze

protection is comparable to the amount of water used for transplant establishment

(Albregts and Howard, 1985; Santos et al., 2011a). Sprinkler irrigation is inefficient due

to the high volumes of water used during the process, most of which drains off and

lowers the aquifer levels. Another effect of using sprinklers is injury on green and ripe

fruit due to the high impact of water droplets (Bish et al., 1997; Domoto, 2006;

Hochmuth et al., 1986; Jackson and Parsons, 1994; Perry, 1998; Poling et al., 1991).

During transplant establishment and freeze protection, the amount of water needed can

be reduced with intermittent intervals and reduced-volume sprinklers (e.g. 13 L m-1)

since these sprinklers are set for the worst scenarios (Albregts and Howard, 1985;

Golden et al., 2003). Sprinkler irrigation at the field are set at 17 L m-1 to provide

effective protection to strawberries, and are commonly spaced at 14.6 × 14.6 m, giving

100% overlapping (Locascio et al., 1967). However, when sprinkler nozzle size is

reduced and distance between sprinklers is larger, freeze protection might be

compromised (Fisher and Shortt, 2009; Locascio et al., 1967).

Row Covers

Protected culture is the use of temporary or permanent structures to provide a

modified environment to enhance plant growth (Wells and Loy, 1993; Jensen and

Malter, 1995). Row covers have been used extensively, especially to prolong growing

seasons. During winter, row covers are placed over the crop for two or four weeks to

provide a warmer environment that enhances crop growth (Dickerson, 2009; Wells and

Loy, 1993). During mild winters, row covers have the potential to be used for freeze

protection (Hochmuth et al., 1987). In the 1980’s, row covers started to be used on

commercial farms as an alternative for Florida growers to protect their crops during

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freezing nights (Hochmuth et al., 1986). Row covers are flexible, transparent or semi-

transparent blankets made up of polyethylene, polypropylene, polyester and other

materials. Thickness and weight vary depending on materials and purpose. For freeze

protection, commonly-used row covers are from 20 to 50 g m2, and they are placed only

during the freezing nights (Hochmuth et al., 1986; Perry, 1998; Wells and Loys, 1993).

The mechanism of using row covers is to enclose the mass of air around the plant

canopy, thus keeping radiational heat already absorbed by the plant and soil during the

day. Row covers significantly reduce the effect of wind, evaporative and radiational

cooling, and convection (Hochmuth et al., 1986; Perry, 1998). Heat loss happens with

the interaction of convection and conduction among the soil, plant, air mass and the row

cover. Convection is heat transfer by movement of fluids, in this case the air mass

inside and outside the row cover. Conduction is transference of heat through a solid

material from molecule to molecule due to temperature gradients (Snyder and Melo-

Abreu, 2005). With these two processes happening, the temperature inside row covers

decreases gradually but not as fast as the air temperature outside.

Using galvanized or fiberglass hoops is a common practice to anchor the row

covers. Another method is placing the row cover with the crop supporting it (Wells,

1996). When row covers are placed without hoops, leaves touching row covers might be

damaged (Dickerson, 2009; Perry, 1998). Using hoops might prevent damage on leaves

and at the same time the air mass around the plant canopy will increase, offering more

crop protection. Width ranges between 3 to 15 m, which means that between 2 and 12

beds could be covered at the same time (Wells, 1996). Degrees of protection

accomplished with row covers vary from 2 to 7°C, depending on the material and

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thickness (Dickerson, 2009; Hochmuth et al., 1993; Poling et al., 1991; Santos et al.,

2011a). An advantage of using row covers is that these materials would not increase

damage on fruit as may happen when using sprinkler irrigation (Perry, 1998). One of the

major limitations for this system is the high labor cost, which is about $370 per ha

(Dickerson, 2009; Wells and Loy, 1993).

Crop Protectants

Crop protectants provide protection reducing environmental stress on plants.

During transplant establishment, naturally-occurring materials, such as kaolin clay,

calcium carbonate, and aluminum silicate are applied on plant canopies. They act as

reflective barriers to decrease ultraviolet and infrared radiation, therefore reducing heat

stress on plants (Glenn and Puterka, 2005; Glenn et al., 2002 and 2003). Crop

protectants are widely used to reduce sunburn and decrease pest incidence on fruit

such as apple (Malus domesticus), pear (Pyrus spp.), tomato (Solanum lycopersicum),

and pomegranate (Punica granatum) (Cantore et al., 2009; Glenn and Puterka, 2005;

Glenn et al., 2002; Melgarejo et al., 2004). Previous studies reported that the application

of kaolin clay, reduced evapotranspiration rates and temperature on leaf and fruit by 2

to 5oC in apple and pomegranate (Glenn et al., 2002; Melgarejo et al., 2004; Wand et

al., 2006). White coats also help to reduce pest incidence such as thrips (Frankliniella

spp.), and increased bud development and fruit set in blueberry possibly due to reduced

heat stress (Vaccinium spp.) (Spiers et al., 2005). Crop protectants for transplant

establishment could be an alternative to using sprinkler irrigation to decrease

temperatures and improve transplant establishment. A study conducted in strawberries,

resulted in 98% plant survival and no negative effects in plant growth or early yield

(Santos et al., 2012).

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Root-dipped crop protectants are materials based on water-absorbent crystal

polymers that may absorb from 100 to 1000 times of their weight in water. The most

commonly used polymers in agriculture are cross-linked polyacrylamides and cross-

linked acrylamide-acrylate copolymers. These materials last between 5 to 7 years in the

soil and break down into ammonium, carbon dioxide, and water (Ekebafe et al., 2011).

They are used especially in dry, arid areas for soil remediation and landscaping where

water is a limited resource to establish new seeds (Wallace and Wallace, 1989). The

polymer concentrates moisture around the root system, improving water use and

fertilizer efficiency (El-Hady and Wanas, 2006; Wang and Boogher, 1987). The amount

of water available for plant uptake varies between 40% and 95% depending on the

cross linking and material (Wallace and Wallace, 1989). Many studies conducted in arid

areas to establish tree species reported increases on plant survival, and shoot and root

biomass (El-Hady and Wanas, 2006; Orikiriza et al., 2009; Pery et al., 1995). The same

response was observed when the polymer was used to establish fruit and vegetable

crops such as citrus and muskmelon (Cucumis melo) (Arbona et al., 2005; Hodges et

al., 2006).

Bioproducts are especially used in organic agriculture where the use of chemical

products is restricted. Regalia® is a plant extract from Reynoutria sachalinensis

commonly used in organic agriculture to control some bacterial and fungal diseases in

strawberry, tomato, and blueberry (Hai, 2012; McGovern et al., 2012). The mechanism

of action is given by systemic acquired resistance (SAR) in plants, which is a natural

defense response resulting from the exposure of plants to a pathogen. The product

application promotes an increase in phenolic compounds and pathogenesis related

25

proteins with antifungal properties, providing resistance to a broad spectrum of

microorganisms (Glazunova et al., 2009). The biofungicide application in cucumber

(Cucumis sativus) caused an increase in phytoalexins after the exposure to powdery

mildew caused by Sphaerotheca fuliginea (Daayf et al., 1997). Another study conducted

in 2009, reported enhanced photosynthetic activity in bean seeds (Vicia faba)

(Glazunova et al., 2009). Karavaev et al. (2008) reported increase in number of stems

and total mass of the grains after the biofungicide application in barley (Hordeum

vulgare) cultivars. Product effectiveness is determined by the rate of application and

disease pressure, being more effective as a preventive than as a curative treatment

(Konstantinidou et al., 2006).

There are many chemical products for freeze protection that are intended to

prevent or reduce freezing damage on plant tissue. The mode of action of these

products varies depending on the composition. Some of them are antitranspirants that

create a physical barrier, reducing heat loss from the plant tissue (Burns, 1970).

Desikote Max® (40% di-1-p-menthene) is based on polymeric terpenes derived from

resins. Different studies have been conducted using similar products with inconclusive

results. Research conducted with young citrus plants using 12 antitranspirants resulted

in no protection in treated plants with minimum temperatures of -4 and -5oC (Burns,

1970). Another study conducted in tomato, pepper, and peach plants using a

cryoprotectant and an antitranspirant did not provide freeze protection when

temperature decreased to -1 and -3.5oC (Aoun et al., 1993; Perry et al., 1992). However,

a study conducted with grasslands roa (Festuca arundinacea) resulted in 22% higher

seed yields compared with the unprotected seeds when temperature went down to -2

26

and -1oC (Hare, 1995). Winter application on cranberries (Vaccinium macrocarpon)

resulted in higher fruit number and yield compared with the non-treated plots (Sandler,

1998). Gardea et al. (1993) reported positive results when using an antitranspirant to

protect grape (Vitis vinifera) plants at -2oC. However, at lower temperatures limited

protection was found.

27

CHAPTER 3 COMPARISON OF FOLIAR AND ROOT-DIPPED CROP PROTECTANTS FOR

STRAWBERRY TRANSPLANT ESTABLISHMENT

Overview

Sprinkler irrigation is used regularly used to establish strawberry bare-root

transplants. When water is applied on plant canopies, it reduces heat stress by lowering

temperatures around crowns and promoting new growth. This growing phase consumes

about 4500 m3 ha-1 of water, which is equivalent to one-third of the volume of water

used during the season (Albregts and Howard, 1985). Most of the applied water ends

running off into drainage canals, leaching nutrients from root zones, and lowering

aquifer levels (Bish et al., 1997; Domoto, 2006; Hochmuth et al., 1986). Water use for

strawberry production is a concern due to competition between agriculture and

urbanization for its use. Sustainable alternatives to reduce the amount of water used

during strawberry production are important.

Crop protectants for transplant establishment could be suitable alternatives to

reduce water volumes during transplant establishment. These products are used as

foliar or root-dipped applications. Foliar applications are usually based on naturally-

occurring materials that create a reflective coat reducing heat stress on transplants

(Glenn and Puterka, 2005; Glenn et al., 2002, 2003). Water-absorbent polymers and

biofungicides are utilized for root-dipped applications. Root-dipped crop protectants

concentrate moisture around crowns and help to prevent bacterial or fungal diseases,

as well as promoting development of beneficial soil organisms (Ekebafe et al., 2011;

Hai, 2012; McGovern et al., 2012; Wallace and Wallace, 1989). The objective of the

studies were to determine the effects of using crop protectants on strawberry transplant

establishment growth and early marketable yield.

28

Materials and Methods

Two separate studies were conducted during the 2012-13 season at the Gulf

Coast Research and Education Center (GCREC) of the University of Florida in Balm,

FL. The soil at the experimental site was a Myakka fine sand siliceous hyperthermic

Oxyaquic Alorthod with 1.5% organic matter and pH of 6.6. Prior to the experiment the

soil was tilled twice at approximately 20-cm deep to ensure proper soil structure. In late

August, planting beds were formed using a standard bedder measuring 69-cm wide at

the base, 61-cm wide at the top, 20-cm high, and 33 cm apart between bed centers.

Simultaneously with bedding, the soil was fumigated with 1,3-dichloropropene plus

chloropicrin (40:60 v v-1) at a rate of 336 kg ha-1. One drip tape line (0.03 L m-1 per min,

30 cm between emitters; T-Tape Systems International, San Diego, CA) was buried 5

cm below the surface. Beds were covered with high density black polyethylene mulch

(0.025-mm thick; Intergro Co., Clearwater, FL). Transplants were set in double rows

with 30 cm separation between rows, and transplants were spaced 38 cm from each

other.

Plant nutrients, such as N, K, Mg, Fe, Zn, B, and Mn were applied following the

current recommendations for the crop in the state (Santos et al., 2011b). Daily fertilizer

application started at two weeks after transplanting (WAT) through the drip lines using a

hydraulic injector (Dosatron, Clearwater, FL). Irrigation volume was the equivalent to the

average reference evapotranspiration for the area from October to March (Simonne and

Dukes, 2009), and it was split equally into two daily irrigation cycles starting at 8 am and

1 pm, respectively. Recommendations for insect and disease control were followed

depending on pest pressure (Santos et al., 2011b).

29

Bare-root transplants with three to five leaves were brought from nurseries in

Canada (Lareault Nursery, Lavaltrie, Quebec, Canada). ‘Strawberry Festival’

transplants for the foliar crop protectant trial were planted on October 9, 2012. ‘Florida

Radiance’ was used for the root-dipped crop protectant trial, and they were planted in

the field on October 16, 2012. Each plot consisted of 4.6-m long rows with 20 plants and

1.5-m alleys between each plot. The experimental area was set with 17 L m-1 sprinkler

heads spaced at 14.6 m. Immediately after transplanting, sprinkler irrigation was turned

on at 8 am each morning for 8 h day-1. For the foliar application study, treatments were:

a) 10 DSI (control), b) 7 DSI, c) kaolin clay (Surround WP, Tessenderlo Kerley, Phoenix,

AZ) at 28 kg ha-1, d) aluminum silicate (Screen Duo WP, Certis USA, Columbia, MD) at

11.2 kg ha-1, and e) calcium carbonate (Purshade, Tessenderlo Kerley, Phoenix, AZ) at

28 L ha-1. Foliar crop protectants were dissolved in 560 L of water and applied on plant

canopies the next day after 7 DSI. For the root-dipped application study, a water-

absorbent polymer (Supersorb F, acrylamide potassium acrylate copolymer cross-

linked; Engage Agro, ON, Canada) and a biofungicide (Regalia®, 5% extract of

Reynoutria sachalinensis; Marrone Bio Innovations, Davis, CA) were compared after 7

and 10 DSI. Root-dipped crop protectants were applied at the moment of transplanting

at the rate of 10 and 3.5 g L-1 of water, respectively. Sprinkler irrigation was turned on

immediately after transplanting for 7 days. Both experiments were set in a randomized

complete block design with four replications.

To assess the effect of treatments on strawberry growth and development, five-

randomly selected plants were chosen to measure canopy plant diameter at 4, 8, and

12 WAT. Plants in borders were not used for this measurement. The same plants were

30

used for the three observations. Canopy plant diameter was measured perpendicular to

the direction of the rows. Plots were harvested twice a week on Mondays and

Thursdays, marketable fruit was defined as a fruit over 10 g in weight, physiologically

mature with more than 80% dark red skin, and free of defects or disease injury. Early

marketable fruit weight and number were collected for the first 10 harvests to identify

the effects of the crop protectant applications on the early yield. Climate data from

2012-13 season were collected from Florida Automated Weather Network (FAWN).

Maximum and minimum temperatures between 15 to 25 cm above canopy level were

monitored for each treatment with temperature loggers (HOBO data loggers, Onset

Corp., Bourne, MA). Data were analyzed using the general linear model (P≤0.05) and

treatment values were separated using Fisher’s protected least significant difference

tests (Statistix Analytical Software, version 9, Tallahassee, FL).

Results and Discussion

Climatic conditions corresponding to the establishment phase are presented in

Table 3-3. Average minimum and maximum temperatures from 12 to 26 October, 2012

were 18.8 and 31oC, respectively. No rain was reported during this time. From

November to January, 2012, minimum temperatures ranged between 0.6 to 18.9oC, and

maximum temperatures were between 13.9 and 29.4oC. Rainfall volumes were 2.5, 62,

and 7.6 mm, respectively, during the same period.

Foliar Crop Protectant Study

There was no difference in plant diameter among treatments at 4 WAT. Sprinkler

irrigation combined with foliar applications resulted in the same plant diameter as using

sprinkler irrigation alone, values ranged between 15 and 17 cm (Table 3-2). However,

plant diameters at 8 and 12 WAT were affected by the combination of foliar application

31

and days of sprinkler irrigation. The highest values were observed in treatments using

foliar application and 7 DSI alone with 37 cm. Using 10 DSI resulted in 33 cm, which

was the lowest value (Table 3-2). The same tendency was observed at 12 WAT, with no

differences in plant diameter for foliar application treatments and 7 DSI alone, averaging

39 cm. Using 10 DSI showed the lowest plant diameter with 36 cm (Table 3-2).

Early marketable fruit weight and number were also affected by foliar applications

and days of sprinkler irrigation. The highest early marketable fruit weight and number

were observed in plots with 10 DSI and 7 DSI plus foliar applications, averaging 14.8 t

ha-1 and 558,220 fruit ha-1. Using 7 DSI alone affected negatively early marketable fruit

weight and number reducing yields to 11.6 t ha-1 and 464,187 fruit ha-1, which were the

lowest (Table 3-2). Based on field temperature sensors, crop protectants decreased

plant canopy temperature between 1 and 4oC (Table 3-2). Total water used during

transplant establishment in control plots was 5600 m3 ha-1, whereas 3900 m3 ha-1 where

applied when crop protectants were utilized. Therefore, foliar applications had an effect

on strawberry transplant establishment in reducing air temperature around the crowns

and improving plant growth and early yield.

Transplant response to foliar applications might be related to reduction in

environmental stress due to high temperatures. The benefits of foliar applications of

kaolin clay, calcium carbonate, and aluminum silicate has been reported in several

studies. Most of the research shows the effects of crop protectant applications to reduce

fruit sunburn. Glenn et al. (2002 and 2003) conducted several studies to report the

effects of kaolin clay application on apple trees, which resulted in a decline on fruit

temperature, possibly due to increased stomatal conductance associated to reduced

32

leaf temperature and reflection of ultraviolet light (Glenn et al., 2002 and 2003; Glenn

and Puterka, 2005). Jifon and Syvertsen (2003) reported reduction in leaf temperature

and air vapor pressure in grapefruit (Citrus paradisi) trees. Cantore et al. (2009)

observed a reduction in fruit temperature by 4oC and decreased in stomatal

conductance and transpiration. Santos et al. (2012) conducted a study using kaolin clay

during transplant establishment in strawberry where either 7 or 8 DSI followed by the

foliar crop protectant application resulted in 98% plant survival and same early yield as

using 10 DSI. Even when a decrease in photosynthetic activity has been reported while

using these products, application results more beneficial due to an increase in yield

when fruit sunburn is reduced up to 95% (Cantore et al., 2009; Glenn and Puterka,

2005).

Root-Dipped Crop Protectants Study

There was a treatment effect in plant diameter at 4 WAT. The largest plant

diameter was observed in treatments with 7 DSI plus Supersorb F, averaging 19 cm,

followed by 7 DSI plus Regalia® application and 10 DSI, which did not differ between

each other (Table 3-3). Using 7 DSI alone decreased plant diameter by 30% (Table 3-

3). Plant growth at 8 WAT was the same for all treatments ranging from 33 to 37 cm. At

the end of the experiment, plants with root-dipped application showed the widest plant

diameter averaging 41 cm, compared to 36 cm when sprinkler irrigation was used alone

(Table 3-3).

Early marketable yield was affected by the combination of root-dipped crop

protectants and sprinkler irrigation during transplant establishment. The highest early

marketable fruit weight was reported in plots treated with either 7 DSI plus the water-

absorbent polymer and the biofungicide or plots that received 10 DSI, averaging 10.6 t

33

ha-1. Using 7 DSI alone decreased early marketable fruit weight to 8.9 t ha-1, which was

the lowest fruit weight value (Table 3-3). Similar effects were observed on early

marketable fruit number. There was no difference among root-dipped treatments and 7

DSI alone with 454,850 fruit ha-1. The lowest early marketable fruit number was

observed in plots with 10 DSI. In conclusion, water-absorbent polymer and the

biofungicide application resulted in the same plant growth and early yield as using 10

DSI. Applying 7 DSI alone produced the lowest yield. This reduction was due to

decrease in fruit size. Total water used during transplant establishment in control plots

was 5600 m3 ha-1, whereas 3900 m3 ha-1 when the crop protectants were applied.

When using Supersorb F, effects on plant growth and yield could be due to

higher water retention around crowns, increasing its availability for plant uptake. This is

a likely advantage for growers since sandy soils are known for their low water holding

capacity. Moreover, response in plant biomass using root-dipped crop protectants has

been described by several authors. Viero et al. (2002) used a water-absorbent polymer

to establish eucalyptus (Eucalyptus grandis) seeds, resulting in optimum plant survival

when using 2 L of water with 12 g of the product incorporated at planting. Furthermore,

Orikiriza et al. (2009) reported an increase in dry shoot and root biomass in eight of nine

tree species planted in pots with 0.2 and 0.4% (w w-1) of a water-absorbent polymer.

Hodges et al. (2006) described an increase in fresh and dry weights and leaf area index

in muskmelon at 3 weeks using a water-absorbent polymer for establishment. The same

response was reported by Woodhouse and Johnson (1991) when applications up to

0.5% (w w-1) in potted barley increased up to six-fold seedlings dry weight. Additionally,

superabsorbent polymers are commonly used for soil remediation in arid areas where

34

water availability is major issue to establish new seedlings (Ekebafe et al., 2011;

Wallace and Wallace, 1989; Viero et al., 2002).

Plant diameter and early yield was improved when using Regalia®, probably to

the systemic action of the biofungicide, which promoted photosynthetic activity and SAR

activation on the new transplants. Mode of action in seed growth is not well known.

However, several studies suggest that it stimulates photosynthetic activity, which is

possibly related to an increase in electron acceptors in photosystem II. Moreover this

product is an SAR activator that promotes production of phytoalexins and other phenolic

compounds with antifungal properties. Product application resulted in enhancement of

photosynthetic activity in barley, causing an increase of grain dry biomass and number

of productive stems (Karavaev et al., 2008). Moreover, research conducted in bean

leaves (Vicia faba) reported stimulation of photosynthetic activity (Glazunova et al.,

2009). Furthermore, ornamental plants such as Impatients valleriana also showed

increase in dry shoot biomass when using the crop protectant (Cochran et al., 2011).

Response in cotton seedlings was also observed with increased emergence rate and

early growth (Su, 2011). As an SAR activator, biofungicide application in cucumber

resulted in increased phytoalexins production and reduced incidence of powdery mildew

(Daayf et al., 1997). Another study showed that biofungicide application resulted in

reduction of disease incidence probably due to increase in phenolic compounds related

to SAR activation (Wurms et al., 1999). Konstantinidou et al. (2006) reported that

product application had a direct effect in conidial germination, resulting in disease

reduction by 40% to 65% when used in tomato. Product effectiveness is determined by

35

the rate of application and disease pressure, being more effective as preventive than as

curative treatment (Konstantinidou et al., 2006).

In conclusion, foliar applications of kaolin clay, calcium carbonate, and aluminum

silicate during transplant establishment help to decrease the temperature around the

crown, promoting growth in strawberry transplants without reduction in yield. Moreover,

root-dipped application resulted in same plant growth and early marketable yield than

using 10 DSI, probably due to higher water retention around the root area, and possible

plant growth improvement due to photosynthetic activity stimulation and systemic

acquired resistance activation in transplants, promoting root and shoot growth.

Implementation of these techniques for transplant establishment means potential water

savings of about 1700 m3 ha-1 of water, which means that 6.7 million m3 of water in

Plant City area can be saved during the season.

36

Table 3-1. Climate conditions from October 12 to October to October 26 2012, in Balm, Fl.

Air to1 RelHum

avg. Total rain

SolRad avg. Wind speed

Days Avg. Min. Max.

Avg. Min. Max.

oC

% mm w m2

km h-1 12-Oct-12 22.4 16.9 29.0 76.0 0.0 218.7 7.1 2.1 18.4

13-Oct-12 22.8 17.1 29.0 77.0 0.0 202.5 8.8 2.2 25.3 14-Oct-12 24.0 19.1 30.2 81.0 0.0 188.2 7.3 1.9 25.4 15-Oct-12 24.3 20.6 30.4 86.0 0.0 175.9 5.2 0.3 21.3 16-Oct-12 23.1 17.7 29.6 83.0 0.0 180.6 4.1 0.1 13.1 17-Oct-12 21.6 18.0 27.0 90.0 0.0 90.7 3.1 0.0 9.3 18-Oct-12 23.7 18.3 31.0 86.0 0.0 199.8 4.1 0.0 15.8 19-Oct-12 23.4 16.4 30.0 84.0 0.0 193.0 3.8 0.0 14.4 20-Oct-12 22.3 14.5 28.7 70.0 0.0 211.2 5.6 0.1 17.4 21-Oct-12 19.3 12.4 27.1 68.0 0.0 214.8 6.5 0.8 18.2 22-Oct-12 21.5 16.0 28.7 76.0 0.0 181.6 9.0 2.2 23.4 23-Oct-12 21.5 16.7 27.2 82.0 0.0 119.6 7.8 1.9 20.9 24-Oct-12 23.4 18.2 29.5 80.0 0.0 180.8 9.9 2.2 27.5 25-Oct-12 23.0 20.3 27.9 87.0 0.0 96.9 8.9 2.0 25.8 26-Oct-12 24.0 21.2 29.2 75.0 0.0 155.0 12.8 3.8 31.0

1Air to = air temperature measured at 60 cm; SolRad= solar radiation measured at 2 m; wind speed measured at 10 m; ReHum= relative humidity; Avg.= average; Min.= minimum; Max.= maximum.

37

Table 3-2. Effects of foliar crop protectants on plant diameter, and total early fruit number and weight of ‘Strawberry Festival’ bare-root strawberry transplants, 2012-13. Balm, FL.

Treatments

Plant diameter Early yield1

4 WAT 8 WAT 12 WAT Fruit

weight Fruit

number Max. to2

cm

t ha-1 no.ha-1

oC

10 DSI (control) 16 33 b 36 b 15.6 a 554,120 a 34.5

7 DSI 16 36 ab 39 ab 11.6 b 464,187 b 34.5

7 DSI + Surround on the 8th day 15 37 a 40 ab 16.0 a 573,756 a 33.2

7 DSI + Screen Duo on the 8th day 17 37 a 39 ab 13.3 ab 523,245 ab 30.9

7 DSI + PurShade on the 8th day 17 36 ab 39 a 15.6 a 585,352 a 30.1

Significance (P≤0.05) NS * * * *

1Early yield= first 10 harvests; DSI = days of sprinkler irrigation; WAT = weeks after transplanting. 2Max to = maximum temperature 15 cm above plant canopies was measured at 2 pm. NS and * = non-significant and significant at P

38

Table 3-3. Effects of root-dipped crop protectants in plant diameter and total early fruit number and weight of ‘Florida Radiance’ strawberry transplants, 2012-13, Balm, FL.

Treatments

Plant diameter Early yield1

4 WAT 8 WAT 12 WAT Fruit weight Fruit number

cm

t ha-1 no. ha-1

10 DSI (control) 16 b 33 36 b 11.4 a 406,142 b

7 DSI 13 c 34 37 b 8.9 b 419,036 ab

Supersorb F dip + 7 DSI 19 a 37 41 a 10.1 ab 464,162 ab

Regalia® dip + 7 DSI 16 b 37 41 a 10.6 a 481,354 a

Significance (P≤0.05) * NS * * *

1Early yield: First 10 harvests; DSI = days of sprinkler irrigation; WAT = weeks after transplanting. NS and * = non-significant and significant at P

39

CHAPTER 4

COMPARISON OF FREEZE PROTECTION METHODS FOR STRAWBERRY PRODUCTION

Overview

Sprinkler irrigation is the most common method for freeze protection in fruits and

vegetables. Water is used to provide heat energy to keep the plant tissue near or above

0oC and prevent freezing injury. This activity is highly inefficient due to the use of large

volumes of water, which may cause running off to drainage canals, leaching nutrients

from root zones, lowering aquifer levels, and damage of green and ripe fruit (Hochmuth

et al., 1986; Jackson and Parsons, 1994; Perry, 1998). Sustainable ways to reduce

water volume during this stage without compromising crop yield are needed. Most of the

alternatives for freeze protection are based on either adding or keeping the heat around

the plant canopy (Perry, 1998).

Reduced-volume sprinklers, row covers, and crop protectants could be

alternatives to sprinkler irrigation. In general, sprinklers deliver more water than is

needed for crop growth (Fisher and Shortt, 2009). Reduced-volume sprinklers might be

a suitable alternative to decrease water volumes used during freeze protection. Row

covers are flexible blankets that help to decrease the influence of wind, evaporative and

radiational cooling, and convection by keeping higher temperature for longer periods of

time (Hochmuth et al., 1986). Crop protectants provide protection by reducing

environmental stress. When used for freeze protection, they prevent or reduce freezing

damage on plant tissues. The objective of this study was to compare the effects of

reduced-volume sprinkler and non-irrigation alternatives for freeze protection on water

savings, and strawberry growth, early and total marketable yield.

40

Materials and Methods

Field preparation was conducted the same as described in the previous chapter.

‘Strawberry Festival’ bare-root transplants with three to five leaves from nurseries in

Canada (Lareault Nursery, Lavaltrie, Quebec, Canada) were planted on 12 and 16

October 2011 and 2012. Each plot consisted of four 9.1-m long rows with 100 plants

and three replications. A non-treated buffer zone of 7.6-m long at the end of each plot

was set to avoid water overlapping of treatments. Immediately after transplanting,

sprinkler irrigation with 17 L m-1 sprinkler heads was turned on at 8 am each morning for

8 h day-1 during the first 10 days to ensure plant establishment.

Treatments consisted on: a) 17 L m-1 sprinkler heads (4.31 mm nozzle; Rain Bird,

Azusa, CA), b) 13 L m-1 sprinkler heads (3.55 mm nozzle; Rain Bird, Azusa, CA), c) light

row covers on the crop canopy (21 g m2; Gardener’s Suply Company, Burlington, VT),

d) light row covers on 0.5-m high minitunnel hoops, e) heavy row covers on the crop

canopy (31 g m2; Agribon row cover, Environmental Green Products, Phoenix, OR), f)

heavy row covers on 0.5-m high minitunnel hoops, and g) crop protectant polymer

(Desikote Max®, 40% di-1-p-menthene; Engage Agro, ON, Canada).

Treatments were set in a randomized complete block design with three

replications during both seasons. Sprinklers were set at 14.6-m apart. Sprinklers were

turned on when air temperature at 1.2-m above the surface was 1oC and they were

turned off when the ice was completely melted. Row covers were placed between 2 and

5 pm on the afternoon of the forecast freezing event, and they were held using 2 kg

sand bags, and were removed once the freezing event ended. The crop protectant was

applied at the rate of 5.1 L ha-1 at the same time when row covers were placed to allow

the formation of the protective film.

41

Leaf number and plant diameter were measured at 6, 12, and 20 WAT following

the same procedures as the previous chapter. The same parameters were used for

harvest. Early and total marketable fruit weight and number were collected from the first

10 and 24 harvests, respectively. Climate data from 2012-13 season were collected

from Florida Automated Weather Network (FAWN), equipment located at the GCREC.

Temperatures between 15 and 25 cm above canopy level were monitored for each

treatment with temperature loggers (HOBO data loggers, Onset Corp., Bourne, MA).

Data were analyzed as described in the previous chapter.

Results and Discussion

2011-2012 Season

There was no significant season by treatments interaction, however, data were

presented by season. Monthly climate conditions from October 2011 to March 2012 are

presented in Table 4-1. Minimum temperatures ranged from -2.9 to 6.4oC and maximum

temperatures between 28.6 to 32.1oC. About 57% of total rain during the growing

season was recorded in October. Relative humidity was around 79% for the whole

period. Solar radiation ranged between 134 to 217 w m2. FAWN reported 5 freezing and

near freezing nights (≤ 1oC) on January 4th, January 5th, January 15th, February 12th,

and February 13th, with minimum temperatures of -1.3, -2.9, -1.9, -0.8, and -0.4oC,

respectively. Calm wind conditions were reported during most part of the nights.

Minimum temperature directly above crop canopy in covered plots was between

4 and 7oC higher than the outside air regardless the cover weight and the use of hoops

(Table 4-4). Moreover, no water for freeze protection was needed in plots using row

covers and crop protectant, compared with 1135 and 874 m3 ha-1 of applied water when

42

using 17.5 and 13 L m-1 sprinklers, respectively. Water savings when using 13 L m-1

sprinklers was 23% compared with the control (Table 4-2).

Plant number and plant diameter were not affected by treatment application

(Table 4-1). There was no difference in plant diameter at 6 WAT with 41 cm. Plant

growth remained the same at 16 and 20 WAT averaging 43 cm in both sampling dates

(Table 4-1). Treatment application affected early marketable fruit and number. The

highest early marketable fruit weight and number was obtained in plots using light row

covers with hoops, heavy row covers without hoops, and the crop protectant plots,

averaging 5.2 t ha-1 and 226,159 fruit ha-1 (Table 4-2). The lowest yield was reported

when using 17 L m-1 sprinklers to protect the crop with 3.7 t ha-1 and 220,047 fruit ha-1

(Table 4-3). These values were about 30% lower than those obtained in plots where row

covers and the crop protectant were applied. Similar tendency was observed in total

marketable fruit weight and number. Using non-irrigation alternatives for freeze

protection resulted in the highest total marketable fruit weights at the end of the

strawberry season with 23 t ha-1 and 905,709 fruit ha-1 (Table 4-3). Lowest yield was

observed in plots using sprinkler irrigation, regardless of water volume with 17.3 t ha-1

and 889,645 fruit ha-1 (Table 4-2). These values represent approximately 25% more

yield when using the alternative methods, regardless of the output volume used for

freeze protection (Table 4-2).

The first six harvests after January 5th and February 13th, 2012 were analyzed to

identify treatment effects after the freezing nights. Crop protection was affected by

treatment application. For the first event, the highest yield was recorded in plots using

row covers and the crop protectant, averaging 2.96 t ha-1 and 157,758 fruit ha-1. The

43

lowest yield was registered when using 17 L min-1 sprinklers for freeze protection (Table

4-4). Similar results were found for the second freezing event, non-irrigation treatments

had the highest yield with 12.67 t ha-1 and 580,658 fruit ha-1. Reduction in yield using

sprinkler irrigation was 28% (Table 4-4).

2012-2013 Season

The same treatments were repeated during this season. Monthly climate

conditions from October 2012 to March 2013 are presented in Table 4-5. Average

temperature during this period was 18.8oC with minimum temperatures ranging from -

0.2 to 6.4oC and maximum temperatures between 28.1 to 33.2oC. About 40% of total

rain during the growing season was recorded in October, followed by December with

30% of total rain. Relative humidity was around 78% for the whole period. Solar

radiation ranged between 126 to 206 w m2. During this season 3 near freezing nights (≤

1oC) were registered on February 4th, February 18th, and March 4th which required

turning on the sprinkler irrigation. Minimum temperature was 1.5oC, 1oC, and 0.2oC.

Calm wind conditions were observed during these nights.

Minimum temperature directly above the crop canopy in covered plots was

between 2 and 8oC higher than the outside air regardless the cover weight and the use

of hoops (Table 4-7). Regarding water volumes needed for freeze protection, no water

was needed in plots with row covers and crop protectant, whereas approximately 681

m3 ha-1 were used in the control plots (17.5 L m-1 sprinklers) and 525 m3 ha-1 when

using 13 L m-1 sprinklers to protect the crop. Water savings using 13 L m-1 was 23%

compared with the control (Table 4-7).

Plant number was the same through the growing season (Table 4-6). Plant

diameter was not affected by treatment application, there was no difference among

44

treatments at 6 WAT averaging 36 cm, plant growth at 14 cm and 20 WAT remained the

same averaging 42 cm (Table 4-6). There was no difference among the treatments on

early marketable fruit weight and number averaging 8.3 t ha-1 and 425,052 fruit ha-1

(Table 4-7). At the end of the season there was no difference in total marketable fruit

weight and number among treatments with 27.19 t ha-1 and 1,363,876 fruit ha-1 in

average (Table 4-7). All treatments provided the same protection as the 17 L m-1

sprinklers (control) during these mild winter conditions. There was no reduction in yield

due to the use of sprinkler irrigation to protect the crop. Similar results were observed

when analyzing the first six harvests after each near freezing night. All treatments

provided the same crop protection. There was no difference in marketable fruit weight

during the three freezing nights with 11.74, 7.31, and 7.4 t ha-1, respectively. Values for

fruit number were 601,323, 414,307, and 413,202 fruit ha-1, respectively.

Results from this trial are similar to the ones found by several authors. Locascio

et al. (1967) achieved protection in strawberries at minimum temperature of -4.4 when

using 17 L m-1 and 13 L m-1 sprinklers, however when wind speed was higher than 8 km

h-1 or temperature was lower than -4.4oC, reduced-volume sprinkler provided limited

protection. Poling et al., (1991) found that light row covers and heavy row covers

protected strawberries subjected to -4.1oC, no difference was observed in yields

compared with 17 L m-1 sprinkler irrigation. Hochmuth et al., (1993) reported that heavy

row covers from 30 to 50 g cm2 protected strawberry plants at a minimum temperature

of -4.4oC, the same protection was measured when using sprinkler irrigation at 17 L m-1.

Santos et al. (2011) found that row covers provided 7oC of protection when temperature

45

in the outside air was -6oC, reduction in yield was observed when sprinkler irrigation

was used to protect the crop.

Crop protectant application provided freeze protection at -3oC with calm wind

conditions during the recorded freezing nights. While few authors report similar results

to the ones found in this experiment, results may be explained by understanding how

the critical temperature varies depending on plant and organ tissue. Moreover, product

formulation differs among these types of products, and represents a main factor when

choosing a crop protectant for specific areas. Hare (1995) found that application of a

cryoprotectant and biodegradable detergent provided protection to tall fescue seedlings

at a minimum temperature of -2oC, increasing yield by 22% in plots with the crop

protectant. Gardea et al. (1993) reported a reduction in leaf disks injury in grapes by

25% when two types of cryoprotectants were used at a minimum temperature of -2oC.

In contrast to these results, research conducted in pepper and tomato transplants

found no protection at -1 and -3.5oC when using two types of cryoprotectant (Aoun et

al., 1993; Perry et al., 1992). Burns (1970) found similar results in citrus were 12

antitranspirants were tested, no protection was provided at a minimum temperature of -

4 and -5oC. In conclusion, when using freeze protection alternatives, data showed that

alternatives performed the same as sprinkler irrigation in the evaluated conditions.

These alternatives have to be chosen according to the conditions from each place.

During the tested conditions all alternatives protect the crop. However, during hard

freezing nights mixing these techniques might work better than just choosing one

technique. If reduced-volume sprinklers are choose it would mean about 129 m3 ha-1

per freezing night in water savings, which represents about 516,000 m3 in the Plant City

46

area. Moreover, if non-water alternatives are adopted it would mean 561 m3 ha-1 per

freezing night and approximately 2.2 million m3 of water savings in the Plant City area.

47

Table 4-1. Environmental conditions from October 2011 to March 2012. Balm, Florida.

Month Air to Total rain RelHum

SolRad avg.

Avg. Min. Max.

oC

mm % w m2

October 21.3 8.8 30.3 109.2 79 169.82

November 19.1 6.9 29.9 15.0 81 152.58

December 17.6 1.9 28.7 7.6 82 134.64

January 15.2 -2.9 28.6 22.9 75 155.34

February 18.7 -0.8 30.5 14.2 79 155.24

March 21.1 1.7 32.1 21.3 75 217.94

1Air to = air temperature measured at 60 cm; SolRad= solar radiation measured at 2 m; wind speed measured at 10 m; RelHum= relative humidity; Avg.= average; Min.= minimum; Max.= maximum.

48

Table 4-2. Effects of freeze protection methods on plant number and plant growth,

Balm, FL, 2011-12.

Plant number Plant diameter

Treatments

6 WAT 12 WAT 20 WAT

no. ha-1

cm

17 L m-1 sprinklers (control) 41259 40 44 42

13 L m-1 sprinklers 41259 42 44 42

Light row cover on canopy 40972 44 44 41

Light row cover with hoops 41832 42 43 42

Heavy row cover on canopy 42405 41 44 41

Heavy row cover with hoops 41832 40 42 41

Desikote Max® 42978 40 42 43

Significance (P≤0.05) NS NS NS NS

WAT = weeks after transplanting. NS and * = non-significant and significant (P

49

Table 4-3. Effects of freeze protection methods on the minimum seasonal air temperatures in each treatment, water use, and early and total marketable fruit weight and number, Balm, FL, 2011-12.

Early yield1 Total yield2

Water use

Treatments Fruit no. Fruit

weight Fruit no. Fruit

weight

no. ha-1 t ha-1 no. ha-1 t ha-1 m3 ha-1

17 L m-1 sprinklers (control) 220047 d 3.68 c 889645 c 17.83 b 1135

13 L m-1 sprinklers 259587 bcd 4.32 bc 863858 c 16.74 b 874

Light row cover on canopy 248397 bcd 4.47 bc 1101140 ab 23.31 a 0

Light row cover with hoops 318099 a 5.50 a 1137313 ab 22.82 a 0

Heavy row cover on canopy 295066 abc 4.98 ab 1199699 a 23.86 a 0

Heavy row cover with hoops 243150 cd 4.17 bc 1049291 b 21.76 a 0

Desikote Max® 306218 ab 5.06 ab 1170255 ab 23.02 a 0

Significance (P < 0.05) * * * *

Early yield= first 10 harvests; Total yield= 30 harvests. NS and * = non-significant and significant (P

50

Table 4-4. Effect of freeze protection methods on the minimum seasonal temperature for each treatment, and the first six harvests after a freezing event on strawberry marketable fruit weight and number, Balm, FL, 2011-12.

Jan. 4th, 2012 Feb. 13th, 2012

Treatments Fruit

number Weight number Min. To1 Fruit number

Weight number Min.To

no. ha-1 t ha-1 oC no. ha-1 t ha-1 oC

17 L m-1 sprinklers (control) 126930 c 2.19 c -2.9 476196 bc 10.20 bc -0.4 13 L m-1 sprinklers 1432627 bc 2.59 bc -2.9 399411 c 8.27 c -0.4

Light row cover on canopy 153861 bc 2.88 ab 0.6 597675 a 13.26 a 4.6 Light row cover with hoops 177928 a 3.28 a 0.6 557570 ab 12.2 ab 5.2 Heavy row cover on canopy 153861 abc 2.91 ab 0.6 625181 a 13.41 a 7.0 Heavy row cover with hoops 142402 bc 2.69 abc 0.6 546104 ab 12.2 ab 7.0

Desikote Max® 160737 ab 3.03 ab -2.9 576764 a 12.47 a -0.4 Significance (P < 0.05) NS * * *

1Min. To = minimum air temperatures in the row covered plots were taken 15 cm above plant canopies, whereas the temperatures in the sprinkler-treated plots were the air temperatures without irrigation. NS and * = non-significant and significant (P

51

Table 4-5. Environmental conditions from October 2012 to March 2013. Balm, Florida.

Month Air to Total rain RelHum

SolRad avg.

Avg. Min. Max.

oC

mm % W m2

October 22.5 6.4 33.2 83.8 82 170.2

November 16.7 3.6 28.5 2.5 79 144.4

December 17.0 0.6 28.1 63.5 81 126.3

January 17.9 2.9 29.5 7.6 81 130.4

February 17.1 0.1 30.4 25.4 77 167.6

March 15.1 -0.2 29.8 25.4 68 206

1Air to = air temperature measured at 60 cm; SolRad= solar radiation measured at 2 m; wind speed measured at 10 m; ReHum= relative humidity; Avg.= average; Min.= minimum; Max.= maximum.

52

Table 4-6. Effects of freeze protection methods on plant number and plant growth, Balm, FL, 2012-13.

Plant number Plant diameter

Treatments

4 WAT 8 WAT 12 WAT

no. ha-1

cm

17 L m-1 sprinklers (control) 42978 35 42 43 13 L m-1 sprinklers 42978 37 43 42

Light row cover on canopy 42978 35 42 42 Light row cover with hoops 42978 34 39 42 Heavy row cover on canopy 42978 34 43 41 Heavy row cover with hoops 42978 36 43 42

Desikote Max® 42978 37 41 41 Significance (P≤0.05) NS NS NS NS

WAT = weeks after transplanting. NS and * = non-significant and significant (P

53

Table 4-7. Effects of freeze protection methods on the minimum seasonal air temperatures in each treatment, water use, and early and total marketable fruit weight and number, Balm, FL, 2012-13.

Early yield Total yield

Water use

Treatments Fruit no.

Fruit weight Fruit no.

Fruit weight

no. ha-1 t ha-1 no. ha-1 t ha-1 m3 ha-1

17 L m-1 sprinklers (control) 437516 8.70 1304812 25.77 681

13 L m-1 sprinklers 554416 8.71 1518843 28.12 525

Light row cover on canopy 357577 7.23 1297936 26.68 0

Light row cover with hoops 399695 8.17 1476724 29.69 0

Heavy row cover on canopy 400555 8.08 1326301 26.27 0

Heavy row cover with hoops 379066 7.83 1329739 27.49 0

Desikote Max® 405712 8.17 1292778 26.30 Significance (P≤0.05) NS NS NS NS NS

NS and * = non-significant and significant (P

54

Table 4-8. Effect of freeze protection methods on the minimum seasonal temperature for each treatment, and the first six harvests after a freezing event on strawberry marketable fruit weight and number, Balm, FL, 2012-13.

Feb. 4th, 2013 Feb. 18th, 2013 Mar. 4th, 2013

Treatments Fruit

number Weight number Min. To1

Fruit number

Weight number Min. To

Fruit number

Weight number Min. To

no. ha-1 t ha-1 oC no. ha-1 t ha-1 oC no. ha-1 t ha-1 oC

17 L m-1 sprinklers (control) 552697 10.77 1.5 444392.52 7.94 1.0 481353.6 8.77 0.2

13 L m-1 sprinklers 598254 11.79 1.5 490809 8.98 1.0 513157 9.51 0.2

Light row cover on canopy 600832 11.96 6.5 379926 6.77 2.7 377347 7.01 3.4

Light row cover with hoops 669597 12.74 6.7 406572 7.05 1.3 384223 7.00 2.7

Heavy row cover on canopy 591377 11.30 9.9 393678 6.40 7.5 381645 6.30 6.4

Heavy row cover with hoops 635215 12.54 7.3 402274 7.04 3.2 379926 6.51 3.6

Desikote Max® 561293 11.07 1.5 382504 6.95 1.0 374768 6.90 0.2

Significance (P≤0.05) NS NS NS NS NS NS

NS and * = non-significant and significant (P

55

CHAPTER 5 CONCLUSIONS

Based on the results from the foliar crop protectant trial, applications during

transplant establishment help to decrease the temperature around the crown, promoting

growth in strawberry transplants. No reduction in yield was observed, regardless of the

material. Furthermore, root-dipped application treatments resulted in the highest plant

diameter and the same yield as using 10 DSI, this result was probably due to higher

water retention around the root area. Biofungicide application also helped to improve

transplant establishment possibly due to stimulation of photosynthetic activity and

systemic acquired resistance activation in transplants, promoting root and shoot growth.

All crop protectants combined with 7 DSI resulted in the same early yield as using 10

DSI. When using 7 DSI alone, plant growth was not affected at the beginning of the

season. However, later effects were observed on early yield, where reduction in fruit

weight and number was found.

It is estimated that about 9.4 L h-1 of diesel fuel are needed to pump water to

irrigate 1 ha. If sprinkler irrigation is used for 8 h day-1, cost of pumping will be about

$240 for three days. Pumping costs are comparable with costs when using crop

protectant applications. Growers will be able to choose among the alternatives which

one is the most practical and less costly depending on availability of material for their

area. Cost of foliar crop protectants varies, most of them are between $25 and $90 per

ha, plus cost of application, which is around $85 per ha including labor and tractor fuel.

Foliar applications can be done with the same machinery used for pesticide application.

On the other hand, cost of root-dipped materials is between $50 and $200 per ha.

Implementation of these techniques will have a direct impact on water savings with

56

approximately 1700 m3 ha-1 of water, which means that 6.7 million m3 of water in Plant

City area can be potentially saved during the season.

When using freeze protection alternatives, data showed that alternatives

performed the same as sprinkler irrigation in the evaluated conditions. Reduced-volume

sprinklers provided freeze protection to strawberries. Row covers protected the crop

regardless of material thickness during both seasons. However when analyzing the first

six harvests after a freezing event during 2011-12 season, significant differences where

found. Moreover, the highest yield was found in plots where row covers and crop

protectants were used. During 2011-12 season higher early and total yields were

reported in plots where row covers were used. Use of hoops when putting row covers

had no major effect in degrees of protection and yields. However, in northern areas with

severe freezing events, use of hoops might have an influence increasing air mass and

keeping temperature for longer inside the row cover. When using the crop protectant,

protection was accomplished at minimum temperature of -3oC, where wind speeds

below 3 km h-1 prevailed during most of the night. However, when using this type of

product, growers have to be aware about degrees of protection because at lower

temperature, crop protection might be compromised.

During the strawberry season, about six to eight freezing nights may occur. Cost

of these techniques varies. About 9.4 L h-1 of diesel fuel are needed to pump water to

irrigate 1 ha, which means $80 ha-1 cost of application per night, translated to $640 ha-1

in eight freezing nights. When using the reduced-volume sprinklers, the same plumbing

can be used but it is required to change the sprinkler nozzle size, which will cost around

$250 (approximately $5 per nozzle). Cost of row covers depends on thickness of the

57

material and ranges from $2500 and $3300 per ha, plus labor cost in installing and

removing the covers, which is around $370 per ha. Duration of the material is between 2

and 4 years depending on use and carefulness. One advantage of using row covers is

that water damage in fruits was reduced, increasing marketable yield. Approximate cost

when using the crop protectant polymer is around $80 per ha per night plus cost of

application which is around $85 per ha including labor and tractor fuel. Future research

is needed to determine what the effect of applying once every freezing event would be

since two consecutive freezing nights is most common. These alternatives have to be

chosen according to the conditions from each place. In mild conditions all alternatives

protect the crop. However, during hard conditions with lower temperatures, mixing these

techniques could work better than just choosing one technique. If reduced-volume

sprinklers are chosen it would mean about 129 m3 ha-1 per freezing night in water

savings, which represents about 516000 m3 in the Plant City area. Moreover, if non-

water alternativ