introduction to pecan diseases and general...

Introduction to Pecan Diseases and General Management

Original Presentation by Damon Smith/Jen Olson

Modified and Presented by Jackie LeeHorticulture IPM Extension Specialist

Little Rock, AR

Contact InformationJackie LeeUniversity of ArkansasCooperative Extension Service2301 S. UniversityLittle Rock, AR 72204

501-671-2191 jalee@uaex.edu

Infectious Disease Agents(Pathogens)

• FUNGI: cause the great majority of plant diseases; thousands have been reported

• BACTERIA: six genera are known to cause plant diseases

• VIRUSES: Submicroscopic obligate parasites• NEMATODES: small nonsegmented worms• PHYTOPLASMAS and SPIROPLASMAS:

submicroscopic obligate parasites• PROTOZOANS: motile microscopic animals• PARASITIC PLANTS: use feeding structures to

feed on plants

Fungi

• Most common of plant pathogens• Attack all plant parts• About 16,000 fungal plant pathogens• Unit of infection = spore or mycelium• Multi-celled• Visible, microscopically• E.g. Pecan scab, Powdery mildew• Spread by wind, splash, insects, water,

tools

Mycelium on leaf surface

SPREAD OF FUNGAL SPORES

•Air currents of 1 MPH or more can carry fungal spores long distances

•Spores often form during the night hours when humidity is high

•Become detached with dropping humidity in the morning hours as temperatures rise and air movement increases, and are borne aloft by convection currents created by warming of soil

Spore germination and infection

• Spores require high humidity for development (>90%)

• Spores require water film on the host tissue to germinate

• Many germinated fungal spores penetrate plant tissue directly, or enter through the leaf pores (stomates) or wounds.

• Most conidia can survive from several hours to several days if conditions necessary for germination are not met.

Fungi

Powdery mildew

Pecan scab

PecanHost

Pathogen Environment

Plant Disease Triangle

Example

Fungus: Cladosporium caryigenum

Periods of extended leaf wetness; cool to moderate temperatures

Pecan Scab

Manipulate the Host Component

Host

Pathogen Environment

Host

Pathogen Environment

• Genetic resistance most powerful disease management tool

• Native trees (fewer disease problems)• Plant stress management – Stress

predisposes plants to disease

Manipulate the Environment

• Do not over fertilize – many diseases are more severe when there is an excess of nitrogen available

• Reduce competition for water, light, nutrients

• Provide adequate air movement and light penetration

Host

Pathogen Environment

Host

Pathogen Environment

Reduce Amount of Pathogen

Host

Pathogen Environment

Host

Pathogen Environment

• Exclusion – Preventing the introduction of a pathogen (verify clean planting stock)

• Eradication – Constant observation and early diagnosis is critical

• Sanitation – Removing pathogen infested plant material from the area

• Pesticide Use

Pecan Scab

Jackie Lee, Horticulture IPM Extension Specialist

Pecan Scab Cycle

Fusicladium effusum

Fusicladium effusum

Overwinters as stroma on shucks, petioles, and stems

Spores produced in spring with warmer temps and rainfall

PecanHost

Pathogen Environment

Plant Disease Triangle

Example

Fungus: Cladosporium caryigenum

Periods of extended leaf wetness; cool to moderate temperatures

Pecan Scab

Native vs. Cultivars

Scab Management for Native Pecans

• Open up groves to air and light; remove heavily scabbing trees; promote drainage

• Assess crop load while scouting for casebearer & make spray decision

• Make fungicide applications

Fungicide applications for Native Pecans

1. First casebearer (pollination complete)

2. 1st Cover (2-3 weeks after first casebearer)*

3. 2nd Cover (2-3 weeks later)*4. Subsequent cover sprays as

needed*

Cultivars: More Intensive

Scab Management For Cultivars

• Plant resistant cultivars• Open up orchards to air and light;

promote drainage• Implement a fungicide spray program

1. Phenological Scheduling Method(based on plant growth stage)

2. Pecan Scab Model ???? (weather-based, Internet accessed)

Resistance

Highly susceptible Moderately susceptible Low susceptibility (resistant)

Burkett Caddo BartonSquirrel’s Delight Colby Choctaw

Western Creek GrakingWichita Giles Kanza

Kiowa LakotaMaramec MountMohawk NaconoOconee Osage

Shawnee PeruquePawnee Stuart

Native Trees

Phenological/Plant Growth Method of Fungicide Application

1. Pre-pollination ( ~”parachute” stage of development)

2. First casebearer (pollination complete) 3. 1st Cover (2-3 weeks after first

casebearer)* 4. 2nd Cover (2-3 weeks later)*5. Subsequent Cover sprays as needed*

Scab influence on yield (Bill Reed)

Pecan Scab Advisory Needed

1. Weather-based disease advisory, Internet accessed, location specific

2. Uses weather data from 115 weather stations in the Mesonet system

3. Calculates # scab hours (hours during which temp > 70 F and RH > 90 %) accumulated in last 14 unprotected days towards fungicide application thresholds

4. Also has information on using the advisory, cultivar susceptibilities, fungicide application thresholds, fungicides and rates

Scab Advisory Spray Thresholds

• Highly susceptible cultivars 10 scab hours• Moderately susceptible 20 scab hours• Natives, low susceptibility 30 scab hours

ProductsProduct Active FRAC Rate/AcreTilt propiconazole 3 4-8 fl ozStratego Propiconazole +

trifloxystrobin3,11 10oz

Orbit 45WPAGPAK/SuperTin

Propiconazole+triphenyltin

3,30 Refer to label

Headline SC pyraclostrobin 11 6-7ozMerivon Fluapyroxad+pyra

clostrobin7,11 5-6.5oz

Adament 50WG Tebuconazole+trifloxystrobin

3,11 3-8oz

Topsin M 70WDGTopsin M 70WP

Thiophanate-methyl

1 1lb

Super Tin 80WP Triphenylin hydroxide

30 5-7.5oz

***Labels change, Refer to label before application. Restrictions on numbers of applications and timing (shuck split)

Products

• http://www.uaex.edu/publications/pdf/mp154year2016/mp154completebook2016.pdf

• MP154 Arkansas Plant Disease Control Products

In the future….

Produce decision aides and educational materials

What is needed?????

Farm visits: jalee@uaex.edu479-530-8163

Questions?