The Hudson Valley orchards just experienced strong, wind driven rains that even the stoutest of insecticides cannot stand against. Most growers had covered up late last week and are now faced with the decision of whether or not to cover up after the recent Monday rains.
Rainfall amounts ranged dramatically across the region between 0.16″ to 1.64″ with on-farm weather stations acting as the best source of reliable on-site decision making information. Your rain gauge will be your best indicator, reflective of heavy rain events in small cells passing through the Hudson Valley yesterday.
On farm NEWA station summaries of rainfall measurements for June 19th:
Highland HVRL: 1.64″
New Paltz (Thruway): 1.26″
New Paltz (Town): 1.08″
The loss of insecticide residue from rain puts tree fruit growers at increasing risk based on the insect we’re trying to manage. For control of codling moth (CM), a neonicotinoid with internal worm activity such as Assail applied after rainfall on 1st June will have prevented the early eggs from hatching as the new larva moved from foliage to fruit (Degree Day predictions for Highland emergence on 31 May). If your last application was Actara 25WDG for PC management, which has no activity against CM, you’re in the open and will need to cover with an effective insecticide if CM trap captures are above 5/trap and is a concern due to packout fruit injury last season.
John Wise, Entomologist, Michigan State University Extension has studied and characterized insecticide residual based on active ingredient class and mode of action. His article on this topic is a must read for all growers.
Translaminar materials require 24 hours of drying prior to a rain event to fully move into the developing fruit and leaf cuticle. Neo-nicotinoids, being ‘translaminar’ or locally systemic, generally, have strong weathering capacity within the cuticle up to 0.5″ of rainfall. However, surface residue of these materials is poor after a very brief period and 1″ of rainfall compared to pyrethroids and carbamates. Insects that feed on fruit or foliage will continue to ingest the neo-nic insecticide within the plant tissue after after 1″ of rain.
That includes the leafhopper complex, such as potato leafhopper (PLH) that has been on the wing for the past 7 days. The most effective approach for this insect is not a one shot fix. The insecticide within the plant, not being prone to direct residual removal from rainfall, will likely be diluted by water uptake within the plant under high transpiration rates when there is full sun and wind during days following rain events (no supporting data on this assumption).
Potato leafhopper, unlike codling moth that moves from eggs deposited on leaves to fruit, is a tip feeder. New growth following rains will provide a safe haven for PLH adults and developing nymphs that prefer tip feeding. The white apple and rose leafhopper will feed on older, mature foliage, producing stipling that has little impact on the tree at moderate infestation levels. PLH however will cause ‘hopper burn’ and kill developing growing tips of trees.
Frequent low rate applications of neo-nics such as Provado (some mite flaring observed with this product) or Assail (at 7d intervals) to newly planted trees will significantly reduce stunting from PLH injury to growing terminal shoots during the critical first three years of establishment. Alternate row applications at 7d of low rate neonicotinoid insecticides have been shown to be very effective at reducing injury to the growing terminals, keeping young trees growing toward the top wire.
On the topic of importance for growing and managing newly planted trees for insect pests. The European Corn Borer (ECB) has been laying eggs over the past two weeks in in corn throughout the Hudson Valley. Both Bt products including Dipel and the Spinosad product Delegate are labeled for ECB in NYS. Scouting for frass in young plantings, especially along the orchard edge harboring woody stem perennial hosts such as pigweed and curly dock is critical in maintaining the growing tip of the tree where ECB tend to infest, borrow and kill the terminal bud.
San Jose Scale management (SJS) using contact insecticides and insect growth regulators is upon us. If you have seen injury at harvest last season you will need to invest in managing this insect this season (over the next few days in mid-Hudson Valley). If left untended, the crawlers will be blown hither and yon to leeward, spreading throughout the block and orchard. Although we have observed crawler emergence here in Highland (as of late last week), applying contact residue for SJS is critical. If you have an infested tree you are monitoring daily for emergence (using black electrical tape and Vasoline to capture and see the minute yellow crawlers) you will know when emergence takes place on in your orchard to the north of HIghland where SJS may have yet to emerge. Insecticide use guidelines / selection for SJS management here.
White cap phase in just beginning. Maintaining effective residue levels is critical or you will miss the management window and end up with red dots on fruit in infested trees. Two applications of contact insecticides such as Imidan or IGR’s (Centaur or Esteem, with or without a penetrant such as 0.25% horticultural oil) are essential at 10-14 day intervals to management this insect during the complete 1st generation emergence, unless you have applied SJS management tools such as IGR’s or Lorsban pre-bloom or made post bloom applications of IGR’s or Movento. At this point a Movento (spirotetramat), a systemic insecticide will not have enough time to effectively move into the foliage and translocate throughout the stems to control the early emmerging SJS crawlers as they began moving out from scale covering this week in the mid-Hudson Valley. However, Movento will likely provide management for the latter emergence, applied during the first emergence window in combination with a contact insecticide for newly emerging crawlers.
In the past we could take a breath during this window and stretch the schedule a bit. However, if you are relying on the OP’s to manage codling moth and San Jose crawlers you will need to re-cover if you have had over an inch of rain. Forecasts are calling for Wednesday & Thursday (June 21-22) morning to provide low wind conditions with a slight chance of rain Wed. afternoon.
Finally…It’s not too early to be concerned about obliquebanded leafroller (OBLR) with first trap capture on the 30th of May and predictive model for the larval emergence June 15th. “Protective sprays with the first spray timed to coincide with the first hatch of larvae at approximately 350 DD base 43F after biofix followed by a second spray 10-14 days later are recommended in orchards that have had a past history of severe OBLR fruit damage or if populations of overwintering larvae were high” (NEWA). However, if you plan to use the Group 28 diamides Exirel ( Altacor (chlorantraniliprole) or spinosyns (Delegate or Entrust for organic growers) product for OBLR, early applications of these products to also control CM would be very effective…. and rainfast, likely to linger a bit longer for OBLR management when the applications are needed in earnest over the next 2 weeks. Note that the Bt products are not very effective against the codling moth but highly effective against the OBLR early larval stage. Insecticide use guidelines / selection for OBLR management with varying degree of efficacy for CM control.
And lastly… Again…read John Wise’s research on rainfastness of insecticides. It should help guide you through your questions on whether (when) to spray after a rain.