Contents
Bacterial Spot (Xanthomonas arboricola pv. pruni)
Perennial (cytospora, valsa) Canker
Phytophthora Root and Crown Rots
European Red Mite, Twospotted Spider Mite
Lesser Peachtree Borer, Peachtree Borer, American Plum Borer
Table 43. Pesticide Spray Table – Plums and Prunes.
43a. Plant Growth Regulator Use in Plums and Prunes
Diseases
Bacterial Spot (Xanthomonas
arboricola pv. pruni)
• Biology & Cultural
Bacterial spot can be devastating to plums and prunes. Plum or prune varieties developed in drier climates and then grown in the more humid climate of NY are the most likely to be susceptible. This disease will be more severe in the warmer southern portions of NY, in wet years, in orchards with lighter (sandy) soils, and in windy orchard sites. The bacterial spot pathogen, Xanthomonas arboricola pv. pruni infects leaf scars at leaf drop and overwinters in infected twigs. Bacteria populations subsequently multiply during warm weather and ooze out during spring rains. Immature tissues are less susceptible to the bacterial infection, and as such, infections will not begin until petal fall/shuck split. Early season copper applications applied to manage bacterial blast are quite effective for controlling the bacterial spot populations, but also likely to induce phytotoxicity if one is not careful.
• Pesticide Application Notes
Unfortunately, there are no materials registered for bacterial spot on prunes and plums. Despite the effectiveness, do not make a dormant copper application for bacterial spot. Copper applications to manage bacterial blast are still allowed whether or not the planting has bacterial spot.
Black Knot
• Biology & Cultural
[1.1] Fungicide sprays will be relatively ineffective in controlling black knot unless old knots are pruned and removed or burned, preferably before bud break. Make pruning cuts at least 6–8 inches below visible swellings. Destroy wild plum and cherry trees along fence rows, for these are major sources of black knot inoculum.
[1.2] The most important period for black knot sprays is from white bud through shuck split. Black knot infection periods require rain and are most likely at temperatures above 55° F; thus, sprays are most likely to be beneficial under these conditions.
Refer to the reference materials list at the end of this publication for a Fact Sheet containing more details on the biology and management of this disease.
• Pesticide Application Notes
[1.3] Captan may cause injury on Stanley and Japanese-type plums if used repeatedly in early season sprays.
[1.4] Bravo and Echo are the most effective fungicides for black knot control. Topsin M is only moderately effective. Bravo and Echo are not labeled for use on plums after shuck split.
[1.5] If leaf spot has been a problem in previous years, include captan, sulfur, or Topsin M in each spray from petal fall until terminal growth stops. Pristine also controls leaf spot. A petal fall spray of Bravo or Echo is recommended if wet weather and inoculum availability favor black knot infection. This spray will also protect against early season brown rot infections of the green fruit.
[1.6] If black knot is present in the orchard or nearby, apply an appropriate fungicide in the first 2 cover sprays if weather conditions are favorable for infection (wet).
[1.7] Vangard may not be applied after bloom.
Brown Rot
• Biology & Cultural
[2.1] Blossom blight is most likely to be a problem when the weather is warm (above 60° F) and wet or when large numbers of fruit were left unharvested the previous year. Blossom blight may also be a problem at lower temperatures if prolonged wetting periods occur. If these conditions do not occur, it is recommended that the white bud, bloom, and petal fall sprays be directed primarily at black knot. Bravo and Echo give superior control of black knot and will also control blossom blight.
Refer to the reference materials list at the end of this publication for a Fact Sheet containing more details on the biology and management of this disease.
• Pesticide Application Notes
[2.2] Captan may cause injury on Stanley and Japanese-type plums if used repeatedly in early season sprays.
[2.3] Some plum cultivars are very susceptible to brown rot for the first few wk after setting; therefore, the shuck split and first cover sprays are important for control of this disease unless the weather is very dry. Do not apply Topsin M without captan.
[2.4] Spray intervals should be shortened during wet periods and the last 3 wk before harvest, because this is when fruit are most susceptible to infection. Pristine and Orbit are the best materials for brown rot control if high disease pressure develops near harvest, because of their partially systemic and antisporulant activities. Orbit is labeled for use beginning 3 wk before harvest.
[2.5] Note the label warning that Orbit may affect the size and shape of “Stanley” plums.
Peach Scab
• Biology & Cultural
Peach scab can infect Japanese plum fruit in southeastern New York if spring weather is warm and wet and no fungicides are applied at shuck split and first cover. The disease is more common following a year when spring frosts caused a crop failure, because trees grown for an entire summer without fungicides are more likely to carry peach scab infections the following year. Fungicides applied to control black knot are usually sufficient to control peach scab.
• Pesticide Application Notes
[3.1] Apply 2 or 3 sprays at 10–14-day intervals beginning at shuck split. Under light disease pressure, a single application of Bravo or Echo applied at shuck split may provide season-long control. Bravo and Echo cannot be applied after shuck split.
Perennial (cytospora, valsa)
Canker
• Biology & Control
[4.1] Perennial canker can be serious on Japa-nese-type plums and some prune cultivars. Refer to the discussion on this disease under Peaches. Also, refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this disease.
Phytophthora Root and Crown
Rots
• Biology & Control
[5.1] Although plum rootstocks are relatively resistant to these diseases, Japanese-type plums that are planted on peach rootstocks are at the same risk as peach and apricot trees. Refer to the section on this disease under Peaches.
Refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this disease.
Insects and Mites
Apple Maggot
• Biology & Cultural
Refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this pest.
• Monitoring
[6.1] Suggested action threshold: 1 adult capture on yellow board or red sphere trap.
• Pesticide Application Notes
[6.2] Up to 3 sprays at 10-day intervals, beginning June 20 in Eastern New York, July 1 in Western New York.
European Fruit Lecanium Scale
• Monitoring
[7.1] 1 spray at the end of crawler hatch (mid-June), about 16–20 days after the 2nd plum curculio spray.
European Red Mite, Twospotted
Spider Mite
• Biology & Cultural
Refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this pest.
• Monitoring
[8.1] Suggested action thresholds:
Bud Burst—10% of spurs with eggs
Shuck Split and later—6 motile forms/leaf.
• Pesticide Application Notes
[8.2] Apply acaricides when mites first surpass threshold; do not apply Acramite or Savey more than once, or †Nexter or *Vendex more than 2 times per season. Use lower rate of †Nexter for European red mite, higher rate for twospotted spider mite.
†Nexter not registered for use in Nassau or Suffolk Counties.
Lesser Peachtree Borer,
Peachtree Borer, American Plum Borer
• Biology & Cultural
Refer to the reference materials list at the end of this publication for Fact Sheets containing details on the biology and management of these pests. American plum borer can be a problem particularly in orchards adjacent to other stone fruit plantings.
• Biological & Non-chemical Control
[9.1] In orchards where lesser peachtree borer is the primary borer pest, hang pheromone ties at 100/acre in late May before flight begins. If population is predominantly peachtree borer, use 200/acre.
• Pesticide Application Notes
[9.2] A single postharvest application of *Thionex or 3 sprays of *Asana or *Warrior to trunk and scaffold limbs against larvae: June 1–10, July 7–15, and August 1–10. *Baythroid not labeled for peachtree borer.
Oriental Fruit Moth
• Biology & Cultural
Refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this pest.
• Biological & Non-chemical Control
[10.1] Pheromone disruption is economically justified if 2–3 sprays are normally applied, and if no other insecticide sprays are routinely needed for other pests after petal fall. For this reason, disruption may not be economical for the 1st brood, as plum curculio sprays at this time normally would also control oriental fruit moth. Pheromones should be applied in mid-June before initiation of the 2nd flight; the need for re-application depends on residual field life of specific formulations: Isomate-M 100, 90 days; Checkmate OFM-F, 14 days. Insecticide sprays or a double rate of pheromones may be needed in border rows of orchards adjacent to sources of adult immigration or in other high pressure situations.
• Pesticide Application Notes
[10.2] Summer sprays should be timed to start approximately at the 10% hatch point, 175-200 DD (base 45° F) after the first adult catch of the second brood, with a second application in 10-14 days. In high pressure blocks, a final spray should be applied 2 wk before harvest to control late season larvae. Suggested action threshold: Avg. of >10 adults/week caught per pheromone trap.
Plum
Curculio
• Biology & Cultural
Refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this pest.
• Pesticide Application Notes
[11.1] Refer to comment [9.2]. Also effective against lesser peachtree borer, eyespotted bud moth, and redbanded leafroller.
[11.2] Frequent applications (7–10-day intervals) of Surround and maximal coverage (minimum of 100 gal/A) are advised in New York while there is active foliar growth.
Redbanded Leafroller
• Biology & Cultural
Refer to the reference materials list at the end of this publication for a Fact Sheet containing details on the biology and management of this pest.
• Monitoring
[12.1] Suggested action threshold: 10% infested terminals from petal fall to shucks off; 5% infested terminals in late August.
• Pesticide Application Notes
[12.2] *Imidan applied as the 2nd plum curculio spray controls this pest. May also need a spray 3 wk before harvest.
Storage Rots
• Pesticide Application Notes
[13.1] A postharvest treatment with Scholar SC via dipping, flooders, T-jet, or similar system for control of storage rots is recommended for fruit coming from orchards where sporulating brown rot was observed, or when one hopes keep fruit in cold storage for a few days prior to sale. Holding tanks in postharvest treatment equipment must have excellent agitation to keep fungicides in suspension. Solutions must be replenished regularly as directed on the product label. Never exposed treated fruit to direct sunlight. This will cause the fungicide to break down.