WNC Orchard Insect Pest Populations – April 21, 2020

— Written By and last updated by

Cool Weather Suppresses Insect Activity

Picture of apple orchard

With phenological stages ranging from petal fall to first cover throughout the region, insects of key concern remain the same as those discussed in last week’s update – plum curculio and oriental fruit moth for those at petal fall, and codling moth will become more important for those approaching first cover. However, the cool weather during the past week has suppressed activity of OFM and codling moth. These moth pests are most active in the first few hours after dusk, but only when temperatures exceed 62 to 65°F. With the cool temperatures during the past week, pheromone trap captures declined considerably this week compared to last week. With cool temperatures forecast for the next week, expect pheromone trap captures to remain low.

In contrast to moth pests, plum curculio is active during daylight hours when temperatures exceed 60°. Considering that daytime temperatures have often exceeded 60° in the past week (albeit, for only a few hours), the potential for damage still exists with this pest, although there is likely to be less damage than when temperatures exceed 70°.

Petal Fall Insecticide Recommendations:

In last week’s table of petal fall insecticide recommendations, I forgot to include the new diamide insecticide Verpedryn 100SL, which was approved for use on apples last fall. This insecticide belongs to the same class of insecticides that includes Altacor and Exirel. Hence, for rotational purposes it should be considered as having the same mode of action as these products. Similar to other diamides it is highly effective against key lepidopteran pests (OFM, codling moth, leafrollers, etc.), but also has exhibited good activity against plum curculio.

Relative Efficacy Chart for Petal Fall Insecticide Options

(― = No activity; P = poor; F= Fair; G = Good, E = excellent)

Insecticide Plum curculio Oriental fruit moth Rosy apple aphid Toxicity to bees
Actara E F E Highly toxic
Altacor E Low toxicity
Assail F G E Mod. toxic
Avaunt G G Mod. toxic
Beleaf E Low toxicity
Delegate P E Mod. toxic
Imidacloprid P P E Highly toxic
Imidan E E Mod. toxic
Sivanto E Low-Mod toxicity
Verdepryn G E Highly toxic
Versys E Low toxicity
Voliam Flexi* E E E Highly toxic

*Voliam Flexi is a premix that includes thiamethoxam (Actara) and chlorantraniliprole (Altacor)


Learn more about southeastern apple insect pests at the Apple Insect Management page.


2020 Average Weekly Trap Captures

HENDERSON COUNTY
Insects per trap
Apr 7 Apr 14 Apr 20
Codling moth  0.0 0.0 0.1
Oriental fruit moth 24.5 9.4 0.1
Tufted apple bud moth 0.0 0.0
Redbanded leafroller 0.0 0.0 0.0
Obliquebanded leafroller
Lesser appleworm
Apple maggot (abandoned and research orchards)
Brown marmorated stink bug (commercial) 1.0 0.1
Brown marmorated stink bug (unsprayed) 0.3 1.0 0.1
Spotted tentiform leafminer 0.0 2.0 0.0
Dogwood borer
Peachtree borer 0.0 0.0
Lesser peachtree borer 1.0 0.0
San Jose scale 0.0 0.0 0.0

*Note that these averages illustrate only the timing of insect emergence and fluctuations in populations, and are not representative of population levels in any given orchard. The only way to have an accurate assessment of an individual orchard’s populations is to set up traps in that orchard.


2020 Accumulated Degree Days

HENDERSON COUNTY
Apr 7 Apr 14 Apr 20
Codling moth
Oriental fruit moth (Biofix 3/30) 75 DD 156 DD 185 DD
Tufted apple bud moth

About degree-day models


2020 Pest Trends (click to enlarge)

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Visit WNC Orchard Insect Populations for archived posts.