Since the 31st of May, Hudson Valley orchards have had strong, wind driven rains that even the stoutest of insecticides cannot stand against. Most growers had covered up earlier in the week and are now faced with the decision of whether or not to cover up after the recent Monday-Tuesday rains. Rainfall amounts between 0.9″ to 1.8″ were recorded the region with on-farm weather stations acting as the best source of reliable on-site decision making information. 
NEWA records of rainfall measurements for June 6-8th:
Albany: 1.27
Castletown 1.80″
Kinderhook: 1.54″
Hudson: 0.88″
Red Hook: 0.43
Highland HVRL: 0.89″
New Paltz” 1.57″
Milton: 1.25″
Marlboro: 0.58
The loss of insecticide residue from rain puts tree fruit growers at increasing risk based on the insect were trying to manage. For control of codling moth (CM), a neonicotinoid with internal worm activity such as Assail or Calypso applied after rainfall on 1 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 27 May). Insecticide use guidelines / selection for CM management here. 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 against this insect if CM is a concern.
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.
These 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). 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.
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 yet to observe crawler emergence here in Highland (as of last night), maintaining contact residue for SJS is critical unless you have an infested tree you are monitoring daily from here till emergence (using black electrical tape and Vasoline to capture and see the minute yellow crawlers). Insecticide use guidelines / selection for SJS management here.
Maintaining effective residue levels is critical or you will miss the management window and end up with red dots on fruit in infested trees. Prior to crawler emergence, 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 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 SJS crawlers as they emerge this week in the mid-Hudson Valley.
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 Friday morning to provide low wind conditions.
It’s not too early to be concerned about obliquebanded leafroller (OBLR) with first trap capture on the 29th of May and predictive model for the larval emergence June 14. “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 Belt (flubendiamide) or Altacor (chlorantraniliprole) or spinosyns (Delegate / Entrust (for organic growers) product for OBLR, early applications of these products now for CM would be both very effective and rainfast, likely to linger a bit for OBLR management when the applications are needed in earnest over the next week.
Finally, read John Wise’s research on rainfastness of insecticides. It will help guide you through your questions on whether to spray after a rain.
