Apple Maggot Monitoring and Spray Interval, Background

This model counts accumulated rain and number of days from last spray to estimate when insecticide coverage is no longer sufficient to kill apple maggot flies. This is the recommended date to clean off apple maggot traps and begin counting trap captures again, comparing the total cumulative average caught per trap against the treatment threshold.

The standard threshold for unbaited red sphere traps is a cumulative average of 1-2 AM fly per trap. For traps combined with a fruit odor-bait capsule, the threshold is a cumulative average of 5 AM trap. At least three traps per block should be used to calculate the average.

The “old rule” for the duration of residual protection from a full-dose Imidan or synthetic pyrethroid insecticide with a *** “Good” rating in the New England Tree Fruit Management Guide was when one of the following conditions was met:

2 inches of cumulative rain within the first 10 days after application,
or
1.5 inches of cumulative rain from 10-14 days after application,
or
14 days maximum even if no rain.

That rule was not deemed appropriate for use with insecticides having shorter residual or lower efficacy rating against apple maggot, such as Delegate, spinosad (Entrust), Asana, Avaunt, or carbaryl (Sevin) products.

Each insecticide option for AM control has different characteristics that affect the duration of control after a full-dose, good-coverage application. Some of the key factors are inherent toxicity of the insecticide to the pest; the persistence of residual protection in the absence of rain; the ability of residual protection to resist rain wash off; the ability of the chemical to penetrate into plant tissues for curative activity against eggs.

In a June 2018 Michigan State University Extension article, Rainfast characteristics of insecticides on fruit (Michigan State University MSU Extension), Dr. John Wise reported results from tests with a rain tower to simulate different amounts of rain at one and seven days after application, followed by tests of the residual coverage several key fruit insect pests, including codling moth on apple, but not apple maggot fly. Those findings provided the impetus for devising best guess values for residual efficacy against apple maggot fly on apple.

The following summary table leaves out many of the details that were considered in devising rules for the number of days and cumulative rain since the application. For example, the “Rain resistance” rating summarizes six different ratings for three different rain amounts times two types of plant tissue (foliage and fruit). Because of those omissions, the tentative rule may not seem to fit with the other values shown for that material. In those cases, other factors such as inherent toxicity to the pest not shown in the table influenced the duration guideline.

Duration guidelines were also based on efficacy ratings from:

2018 Cornell Tree Fruit Management Recommendations.
Cornell University Cooperative Extension.
2018 Spray Bulletin for Commercial Tree Fruit Growers.
Virginia, West Virginia, and the University of Maryland Extension.
2017 New Jersey Commercial Tree Fruit Production Guide. Rutgers Cooperative Extension.
Guide to Fruit Production 2016–2017. Ontario Ministry of Food, Agriculture, and Rural Affairs.
Monitoring and management strategies for apple maggot in 2010 (Michigan State University MSU Extension)
July 13, 2010 by John Wise, David Epstein, Larry Gut, and Luís Teixeira, Michigan State University Extension

Insecticide	Efficacy rating	Days residual	Plant pene-tration	Rain resistance	Duration of protection estimate
Imidan Class: Organophosphate IRAC 1B PHI: 7 days	Good to Excellent	14+	Surface	Low	Days 1-6, up to 1.5” rain. Days 7-14, up to 1” rain 15 days maximum even if no rain. Notes: Long history of effective AM control. Poor rain resistance compensated by high efficacy against pest. Long residual in absence of rain. Customer concerns about OPs.
Assail Class: Neonicotinoid IRAC 4A PHI: 7 days Minimum respray interval: 12 days Application limit:	Good to Excellent	14	Trans-laminar & Acropetal	Moderate	Days 1-14, up to 1” rain. 14 days maximum even if no rain. Notes: Proven effective AM control. Lower inherent toxicity to AM than Imidan compensated by rain resistance, and repellence and curative activity against eggs. Customer concerns about neonic impacts on honeybees more relevant to neonics in the nitro group. Assail is not in that subgroup, and has lower acute toxicity to honeybees, but customers concerned about neonics may not be aware of such details.
Pyrethroids Class: Pyrethroid IRAC 3A PHI: Baythroid 7 Danitol 14, Mustang Maxx 14 Warrior 21	Good	7-10	Cuticle pene-tration	Moderate	Days 1-10, up to 1” rain. 10 days maximum even if no rain. Notes: Repeated use of pyrethroids may flare populations of mites, woolly apple aphid, San Jose scale or other pests normally kept in check by biocontrol.
Exirel Class: Diamide IRAC 28 PHI: 3 days	Fair to Good	10	Trans-laminar	Moderate-High	Days 1-10, up to 1” rain. 10 days maximum even if no rain. Notes: Phytotoxicity concerns. Do not tank-mix with strobilurins, copper or captan fungicides. Application within 7-days of these materials, other EC pesticides, or spreader/penetrant adjuvants may increase risk of crop injury.
Asana Class: Pyrethroid IRAC 3A PHI: 21 days	Fair to Good.	7-10	Cuticle pene-tration	Moderate	Days 1-6, up to 1” rain. Days 7-10, up to 0.5” rain 10 days maximum even if no rain. Asana may be less effective above 80º F. Notes: I do not have data to justify separating Asana out from other pyrethroids, but have done so based on concern that it may be more heat-sensitive than 2nd-generation pyrethroids.
Diazinon Class: Organophosphate IRAC 1B PHI: 21 days	Fair to Good	? but less than Imidan	Surface	Low	4-day Restricted Entry Interval. Not enough information to devise rain guideline.
Delegate (spinetoram), Entrust (spinosad). Class: Spinosyn IRAC 5 PHI: 7 days	Fair	7-9	Trans-laminar	Moderate-High	Days 1-7, up to 2” rain. Day 8-9, up to 0.5” rain 9-day maximum even if no rain. Notes: MI Extension rates Delegate and Entrust as for suppression only against AM, suggesting that these materials are not reliable against high AM pressure.
Sevin (carbaryl) Class: Carbamate IRAC 1A PHI: 3 days	Fair	7-9	Cuticle pene-tration	Moderate	Days 1-7, up to 2” rain. Day 8-9, up to 0.5” rain 9-day maximum even if no rain. Notes: While carbaryl acts as a thinner during the fruit set period, it will not have a thinning effect when used in July-August.
Altacor Class: Diamide IRAC 28 PHI: 5 days	Fair	10	Trans-laminar	Moderate-High	Days 1-6, up to 1” rain. Days 7-10, up to 0.5” rain. 10 days maximum even if no rain. Notes: MI lists interval as 10-14, but with Fair rating and for suppression only. Apparently, it lasts well, but has less inherent toxicity against apple maggot than higher ranked alternatives.
Avaunt Class: Oxadiazine IRAC 22 PHI: 14 days	Fair	7-10	Cuticle pene-tration	Moderate	Days 1-6, up to 1” rain. Days 7-10, up to 0.5” rain 10 days maximum even if no rain. Notes: MI Extension gave Avaunt a Poor rating against AM.
Admire Pro Class: Neonicotinoid IRAC 4A PHI: 7 days	Fair	? but less than Assail	Trans-laminar & Acropetal	Moderate	Notes: Admire is a member of the neonic subgroup driving concerns about impacts on honeybees. Not enough information to devise rain guideline.
Surround No IRAC class PHI: 0 days (but application near harvest would exacerbate visible residue)	Fair	Varies with rain	Surface	Low	Requires reapplication after about 0.5” rain, as judged by thorough visible coverage. Deters but does not kill AM so coverage must be maintained through egglaying season. Organically certifiable.
GF-120 Class: Spinosyn IRAC 5 PHI: 0 days	Fair	7-14	Works as bait and kill.		Requires special applicator equipment. Organically certifiable.

This attempt to represent the information on each material as weather-based rules is intended to help growers make decisions about insecticide selection and respray intervals and to update the apple maggot respray interval tables in Ag-Radar. Keep in mind these are just best guesses at summary extensive data into simple rules. Only single active ingredient products are listed. PHI = preharvest interval for apples.

The guidelines shown in the Ag-Radar respray tables assume a moderate level of apple maggot pressure. Once an insecticide application has been depleted by the number of days or rain, clear AM traps and begin counting from zero towards the threshold to see if/when retreatment is needed. More stringent respray guidelines may apply where pest pressure is abnormally high.

The apple maggot cumulative trap catch estimates are derived from the apple maggot emergence model described in Publication – CIPRA – Computer Centre for Agricultural Pest Forecasting: Crop Guide (Government of Canada), 2014. By Dominique Plouffe, Gaétan Bourgeois, Nathalie Beaudry, Gérald Chouinard. and Danielle Choquette.