WNC Orchard Insect Pest Populations – April 14, 2020

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apple orchardPetal Fall Spray Options: In many locations petal fall is approaching, and options for insecticides to spray will depend on what was applied before bloom and whether or not OFM mating disruption is being used. Another consideration is the level of bee activity in an orchard. For insecticides toxic to bees, which include most recommended at petal fall, labels restrict application of those insecticides until after bee hives have been removed from an orchard. Also, in situations where hives are in nearby orchards, applications should not be made if bees are foraging on flowers in the ground cover.

The key pests targeted at petal fall sprays include rosy apple aphid, plum curculio, and oriental fruit moth (OFM). See the table below for insecticide options.

Plum Curculio: This remains one of the most common causes of insect damage to apples in this region, and effective control is highly correlated with petal fall sprays. Although the severity of damage varies considerably among orchards, plum curculio is ubiquitous and can cause damage in virtually every orchard. In orchards with a history of problems, sprays should be made as quickly after petal fall as possible. In orchards where damage is historically low, there is usually a longer buffer period and sprays can be slightly delayed. However, 1st Cover is often too long to wait.

Rosy Apple Aphid:  Rosy apple aphid is a sporadic pest, but it can be difficult to monitor, and control with curative applications of insecticides can be difficult. Most neonicotinoids and closely related insecticides are effective against RAA, and effective control can be achieved when applied before bloom at Pink, or after bloom at petal fall, or in some instances as late as 1st Cover.

Oriental Fruit Moth:  Biofix in at the research station in Henderson County was set on 30 March. Although we did not have traps set off the mountain, biofix is typically at least 7 to 10 days earlier. In orchards using mating disruption for OFM, insecticidal control of the first generation is not necessary, and it is only necessary to focus on plum curculio. However, where mating disruption is not used, an insecticide effective against this pest is recommended to control the first generation.

Codling Moth:  At the research station in Henderson County we have not yet captured our first codling moth. However, they are active off the mountain, with high numbers reported from some locations. It is important to remember that while high numbers can be captured shortly after emergence, there is a lag time between emergence and when egg laying begins. Applications at petal fall or shortly thereafter are not recommended unless relying on insecticides that act primarily as ovicides. However, most recommended insecticides target first instar larvae when they hatch from eggs. Hence, waiting until 200 DD after biofix (about first cover) is sufficient even when early season trap captures are high.

Relative Efficacy Chart for Petal Fall Insecticide Options

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

Insecticide Plum Curculio OFM RAA 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
Imidacloprid P P E Highly toxic
Imidan E E Mod. toxic
Sivanto E Low-Mod 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

Insects per trap
Mar 31
Apr 7
Apr 14
Codling Moth 0.0 0.0
Oriental Fruit Moth 7.5 24.5 9.4
Tufted Apple Bud Moth 0.0
Redbanded Leafroller 4.0 0.0 0.0
Obliquebanded Leafroller
Lesser Appleworm
Apple Maggot (abandoned and research)
Brown Marmorated Stink Bug (commercial – mountains) 1.0
Brown Marmorated Stink Bug (commercial – upper Piedmont)
Brown Marmorated Stink Bug (research – unsprayed) 0.3 1.0
Spotted Tentiform Leafminer 0.0 0.0 2.0
Dogwood Borer
Peachtree Borer 0.0
Lesser Peachtree Borer 0.0
San Jose Scale 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 population is to set up traps in that orchard.

2020 Accumulated Degree Days

 Biofix Apr 7 Apr 14
Codling Moth
Oriental Fruit Moth March 30 75 144
Tufted Apple Bud Moth

About degree-day models