Tulare County
Tulare County |
Prune News (February 2000) |
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 Southern San Joaquin Valley Prune Day
Agricultural Building Auditorium 2500 West Burrel, Visalia | ||
| 7:00 AM | Coffee and Prune Danish Courtesy: Tule River Cooperative Dryers |
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| 8:00 | The Prune Breeding Research Program and
Demonstration - New Release(s) Imminent Jim Doyle, U.C. Staff Research Associate, Kearney Agricultural Center, Parlier |
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| 8:45 |
Potassium for Prunes |
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| Potassium and prune tree needs Steve Sibbett, UCCE Farm Advisor, Tulare Co. New insights into prune potassium management strategies Steve Southwick, U.C. Extension Pomologist |
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| 9:30 | "Ralex" - A New Harvest Management Tool
Steve Southwick, UCCE Extension Pomologist |
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| 9:45 | Break | |
| 10:00 | Managing Brown Rot Themis Michaillides, U.C. Pathologist, Kearney Agricultural Center, Parlier |
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| 10:30 | "ESPS" - A Low Risk Management System for Prunes | |
| Overview: Gary Obenauf, Research Director,
California Prune Board Insect/disease management update under ESPS Walt Bentley, UCCE Area IPM Advisor, Kearney Agricultural Center, Parlier Irrigation management update under ESPS Ken Shackel, Associate Professor, U.C. Davis |
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| 11:30 | Alternate Year Dormant Sprays - Six Years
in the Program Steve Sibbett, UCCE Farm Advisor, Tulare Co. |
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| 11:45 | State of the Industry Rich Peterson, CEO, California Prune Board |
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| 12:15 PM | Adjourn | |
2 hours Continuing Education Credits requested.
As of this writing, we have received .88" of rainfall since July 1, 1999, at the Farmersville CIMIS station. Couple that with temperatures above average and delayed defoliation this past fall (thus actively transpiring trees), soil moisture has been substantially depleted.
Prunes need to start the growing season at "leaf out" with soils at field capacity (moisture remaining after free drainage has occurred - maximum stored water content) to the depth of rooting - at least 5 feet. If trees start out dry it is difficult to maintain continually optimal soil moisture levels with supplemental irrigation during the growing season; when soils dry between irrigations, there simply is no "reserve" for trees to draw upon. Consequences of inadequate soil moisture during the growing season are reflected in poor fruit size, fruit cracking (response of fruit to irrigation when trees are dry in June/July), poor vegetative growth for the 2001 crop, pest problems such as mites and potential damage from this year's dormant spray containing oil.
To ensure adequate soil moisture for spraying and when trees leaf out, winter irrigations may be needed this year to fill the root zone as a supplement to winter rainfall. If rainfall is below normal by late January, a good, deep irrigation is advised. If rainfall is still below normal by mid-February, additional irrigation is suggested - remember, the objective is to wet soils to field capacity to the depth of rooting by the time trees leaf out.
Attached is our year 2000 prune disease control guide for brown rot, russet
scab, and prune rust. As always, read the label carefully before applying any
pesticide.
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Fungicide Efficacy Disease | |||||
| Material | Resistance Risk |
Brown rot | Russet scab | Rust | |
|---|---|---|---|---|---|
| Blossom | Fruit | ||||
| Benlatea + oilb | high | ++++ | ++++ | --- | --- |
| Break EC | high | ++++ | ++++ | --- | ? |
| Rovralb + oilc | low | ++++ | ++++ | --- | +++ |
| Topsina + oilc | high | ++++ | ++++ | --- | --- |
| Abound | high | +++ | --- | --- | +++ |
| Benlate | high | +++ | +/- | --- | --- |
| Rovral | low | +++ | +/- | --- | --- |
| Topsin | high | +++ | +/- | --- | --- |
| Vangard | high | +++ | --- | --- | --- |
| Bravod,e | low | ++ | ++ | ++ | --g |
| Captand | low | ++ | ++ | +++ | --- |
| Funginexf | high | ++ | ++ | --- | --- |
| Rally | high | ++ | ++ | --- | --- |
| Sulfur | low | +/- | +/- | --- | ++ |
Rating: ++++ = excellent and consistent, +++ = good and reliable, ++ = moderate and variable, + = limited and erratic, +/- = minimal and often ineffective, --- = ineffective, and ? = insufficient data or unknown.
a. Strains of Monilinia fructicola and M. laxa resistant to Benlate and Topsin have been reported in some California prune orchards. No more than two applications of Benlate and Topsin should be made each year.
b. Blossom blight only; not registered for preharvest use.
c. The oil is "light" summer oil, 1-2% volume/volume. If applied in summer causes fruit to lose bloom and look red. They dry to normal color.
d. Do not use in combination with or shortly before or after oil treatment.
e. Do not use after shuck split.
f. Label canceled; other companies may produce.
g. Effective but cannot use at proper timing (summer).
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Prune - Treatment Timing
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| Disease | Green bud | White bud | Full bloom | May | June | July |
|---|---|---|---|---|---|---|
| Brown rot | +++ | +++ | ++++ | -- | + | ++ |
| Russet scab | --- | --- | +++ | --- | --- | --- |
| Rust | -- | --- | -- | + | ++ | +++ |
Timings used will depend upon orchard history of disease, length, of bloom, and weather conditions each year.
Brown rot: Flowers are susceptible beginning with the emergence of the sepals (green bud) until the petals fall.
Russet scab: A physiological disorder, no pathogens involved.
Rust: More severe when late spring rains occur.
Dormant application of an organophosphate (OP) or carbamate insecticide plus narrow range oil controls a wide range of pests: peach twig borer, San Jose scale, and, the eggs of aphids (mealy plum and leaf curl) and European red and brown almond mites. It is important to include the oil; it helps the insecticide penetrate target insects or eggs suffocating them.
Here are important guidelines for effective spray application:Use a ground rig, not aircraft.
Drive slowly, 1.5 to 2.0 mph.
Use 4-6 gallons of spray oil/ac with the insecticide.
Spray damp trees (from fog) but not dripping wet trees.
For large trees, two-thirds of the spray material should go into the upper one-half of the tree.
Spray material should dry on the tree before a rain.
Apply 200-400 gal/ac. When applied correctly, concentrate sprays are effective too.
Do not apply sprays containing oil to prunes when fully dormant. Wait until after February 15 and preferably delay treatments until bud swell.
1. Bt: Bacillus thuringiensis (Bt) applied prebloom and at bloom is an effective substitute for "hard" pesticides normally applied during the dormant season for control of peach twig borer (PTB). Bt must be applied twice during bloom development: The first application is put on at the "popcorn" stage, and the second 7 to 10 days later. Bt must be applied by ground rig. It is compatible with fungicides timed for brown rot at those stages of bloom. Remember, Bt does not kill San Jose Scale, aphids, or mite eggs, so monitoring for these pests will be important if this approach is used.
2. Alternate Year Dormant Sprays: In our experiments, applying a dormant spray every other year has been as effective as annual treatments in controlling scale and peach twig borer. If this strategy is used, good spray coverage is essential in the year of treatment; the objective is to reduce the pest level to the point it cannot recover to do economic damage in the year of no dormant spray.
Aphids (mealy plum and leaf curl) are not controlled in a Bt program or in the year no dormant spray is applied in an alternate year strategy. Populations may or may not develop in such orchards. As trees leaf out and grow into April, careful monitoring is needed to detect and treat aphid populations before damage occurs. Aphid outbreaks favor young trees and vigorously growing trees and occur in spots (especially on the edges and next to structures and oak trees). If treatment is required, spray oil or an insecticide with good coverage is effective. See attached oil efficacy for aphids. (Olson, et al, 1999. Butte County.)
Note: Four gallons of commercially applied oil/ac from "green-tip" to "white bud" reduced aphids to sub-economic levels in 5 AC experimental plots (Graph 1). If the dormant spray is eliminated, combining oil with your Rovral treatment during this time for Brown Rot is an effective strategy. Remember, 2 weeks need to elapse between oil and Captan applications.
At this site the dormant treatment completely eliminated aphids while the green tip oil treatment resulted in 10 percent of the trees with aphids. However, the adjacent untreated check area had 40 percent of the trees with aphids (Graph 1). The oil treatment was applied at 1.85 miles per hour and applied between green tip and popcorn bloom. Fungicides for scab were not applied during bloom. The oil treatment reduced the aphid population to a satisfactory level and no further treatments were necessary.
Graph 1.
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