STONE FRUIT IRRIGATIONHealthy mature peaches, plums, and nectarines grown without a cover cropconsume about 38 acre-inches of water per acre per year (3.2 acre-feet water peracre per year). Figure 1 illustrates the water use by month. Only about 25percent of the total water use occurs from March through May, 50 percent fromJune 1 through August and the remaining 25 percent of the seasonal water useoccurs in September and October. It is important to remember this seasonalvariation in water use to avoid tendencies to overirrigate in the spring andunderirrigate during the hot summer months.

Figure 1. Normal year water consumption by healthy, mature peach, plum, and nectarine in the San Joaquin Valleywith a clean cultivated orchard floor.

Acre-Inches Water Use/Acre

Factors Affecting Water Use

Site specific factors can affect the averageyear water usage in the previous figure.Some of the more common factors includelow soil-water availability, real time weatherconditions, variety, rootstock, age andhealth of tree, and presence of a cover crop.

Low soil-water availability in the root zonecan cause mature trees to use less water than

Month

there is inadequate water available foruptake. When water availability isdescribed in the previous figure. The treescan not extract the water from the soil ifrestricted, the trees respond by closing theirleaf pores (stomata) which reducestranspiration and photosynthesis. The resultis reduced bloom, shoot growth, reductionin fruit size and interruption of bud tissuedevelopment for the following year's crop.

Variation in weather conditions between

Written by Allan Fulton and Robert H. Beede, UC Soils and Water Farm Advisor and Pomology Farm Advisor, respectively, KingsCounty. Research contributions from David A. Goldhamer UC Irrigation Specialist, Kearney Agricultural Center.

Stone Fruit - Page 2

seasons can cause the actual water usage tofluxuate as much as 6.0 acre-inches per acreabove or below the averages presented inFigure 1. Variable weather conditionsbetween seasons may enable a grower tosave one or two irrigations or may requireone or two additional irrigations dependingon the season. Variable weather conditionscan be managed with skilled observationsusing soil augers, or other soil basedmeasurements. Real time weatherconditions and estimates ofevapotranspiration for specific areas can beaccessed through the California IrrigationManagement Information System viatelecommunications. Inquiries concerningthis information should be directed to theCalifornia Department of Water Resourcesat (916)-653-9847. The Hanford Sentineland Fresno Bee may also provide real-timeestimates of crop evapotranspiration andpercent variance from normal conditions ona weekly basis in the Farm Section.

There are about 400 commercial varieties ofpeach, nectarine and plum grown inCalifornia. In general, the primary varietiesgrown in the San Joaquin Valley bloomabout the first week of March. Varietal

differences in leafout date will have littleaffect on the total water usage for theseason. However, different varieties willinfluence the rate of fruit development, timeof thinning, and fruit maturity, all of whichwill affect water management.

Tree age and growth rate can affect wateruse by stone fruit. Young trees withdeveloping canopies will use less water thandescribed in the previous illustration. As a

general rule, trees in their first, second,third, and fourth seasons will use about 20,40, 60, and 80 percent of the usagepresented in Figure 1, respectively. Table 1provides estimates of water use as the youngtrees mature.

By the fifth or sixth season, the young treesshould have enough canopy established toconsume the quantities of water illustrated inFigure 1.

Rootstocks affect the rate of tree growth andthe number of years to establish a fullyproducing tree with maximum waterrequirements. Varieties budded on

Nemaguard rootstock are usually morevigorous and develop large canopies earlier

Table 1. Estimates of water by young peach, pi um, and nectarine trees during the first five years of development.Leafout MonthNumber Mar Apr May Jun Jul Aug Sep Oct Total

Inches

I 0.4 0.6 1.1 1.3 1.5 1.3 0.9 0.6 7.72 0.8 1.2 2.2 2.6 3.0 2.6 1.8 1.2 15.43 1.2 1.8 3.3 3.9 4.5 3.9 2.7 1.8 22.14 1.5 2.4 4.4 5.3 6.0 5.2 3.6 2.4 30.85 1.8 3.1 5.5 6.7 7.6 6.4 4.6 3.0 38.7

Stone Fruit - Page 3

than varieties on Lovell rootstock when

planted in nematode infested soils.

Diseases and to a lesser extent insects maycause tree health to decline. As a result,tree growth rate and water use will be lowerthan shown in Figure 1. Routine fieldobservation of soil-water content will be

very important to adjust the irrigationmanagement to the need of declining trees.

Cover crops grown during the seasonincrease water consumption. The valuesgiven for water use by mature, healthy fruittrees grown on clean cultivated orchardfloors should be adjusted upward about 25percent while the cover crop is growing.Cover crops that are controlled withchemical mowing will use very little waterafter chemical treatment.

Irrigating Under Drought Conditions

Irrigating during drought is not a matter ofIF the trees will be stressed, it is a questionof when the trees WILL BE stressed.Successful irrigation during drought must bejudged by the affect of management on thisseason's fruit crop and the followingseason's crop. The impacts ofunderirrigation on this year's crop will mostlikely be less noticeable than the effects thatcarry over to next year.

Early season peach varieties such as Reginaand Springcrest, early season nectarinessuch as Grand and Spring Red, and earlyseason plums such as Red Beaut and SantaRosa are harvested by mid June. These

varieties face the hot summer temperatureswith no fruit on the tree. As a result,research has shown that early varieties cantolerate underirrigation after harvest. Twonegative effects related to underirrigation ofthese early varieties after harvest are greateroccurrence of fruit doubling and deep suturein next year's crop. However, researchindicates that these problems can beminimized if at least 50 percent of thenormal water use from mid June throughJuly is supplied by postharvest irrigations.Meeting the full irrigation requirement at thebeginning of August and continued into midSeptember will also prevent doubling anddeep suture.

Late season varieties such as O'Henry andCal Red peach, Flamekist and AutumnGrand nectarine, and Friar and Casslemanplum require a different managementapproach. Research has shown a reductionin fruit size when water stress occurs anytime fruit is on the tree. The best approachis to satisfy the full water requirement frombloom in early March up to pit hardeningwhich occurs between mid April and midMay depending on variety. During pithardening (about 60 days after bloom), therate of fruit sizing decreases and irrigationmay be reduced to about one-half of thenormal use with no effect on fruit size. Pit

hardening may extend 20-40 days dependingon the late season variety. Resumeirrigation to meet full water requirements assoon as rapid fruit expansion begins and pithardening is complete (about 30-40 daysbefore harvest). Additional water can beconserved by supplying only about one-halfof the full water requirement after harvest.

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