Fruitworm control in blueberries

Checking monitoring traps and weather conditions for cherry fruitworms and cranberry fruitworms can help guide management decisions in blueberry integrated pest management.

Cherry fruitworm emergence has started in southwest Michigan, and the first cranberry fruitworm moths are also being caught in a few sites. This highlights that it will soon be time for protecting the newly forming blueberry fruit from fruitworms. Fields that have some petal fall, a history of cherry fruitworm infestation (a single larva infesting a single berry) and where this moth has been trapped during the past week should be treated at 100 growing degree-days (GDD) after the first moth capture. Depending on your location, that’s likely to be later this week with the warm weather.

As cranberry fruitworm emergence starts in the coming days, Michigan State University Extension suggests checking traps to set the biofix (first sustained moth capture) and then count 100 GDD after the first sustained catch to determine when to protect fields from this pest. There is a degree-day cranberry fruitworm model online at MSU Enviro-weather to help you determine the optimal timing for spraying to protect the small berries. This is likely to occur during bloom, and so it is very important to refrain from using any compounds that are toxic to pollinators when these insects are in your fields. Applications early in the day or ideally late in the evening will help reduce the exposure of pollinators to toxic residues.

Insecticides registered for use during bloom and in the presence of pollinators have provided consistent control of fruitworms in trials at the Trevor Nichols Research Center and at grower fields. These are the B.t. products such as Dipel or Javelin, the bioinsecticides Grandevo and Venerate, and the insect growth regulator Intrepid. The B.t. products have short residual activity, typically around five days, so they need regular reapplication. These are best applied when daily temperatures reach 70 degrees Fahrenheit so the larvae will actively feed and ingest the insecticide. Grandevo and Venerate have demonstrated good efficacy against both fruitworm pests in our recent trials, and both can be used on organic production systems. Intrepid is more resistant to degradation by sunlight and it is much more waterproof once residues are dry, giving between seven and 14 days activity.

Other options for controlling fruitworms during the egglaying period are the growth regulators Rimon and Esteem. These insecticides are highly active ovicides and they also disrupt the adult moth’s ability to lay viable eggs, hindering the development of larvae. As with all insecticides, be sure to follow the label restrictions if making applications while bees are foraging in the fields, and do whatever you can to reduce the risks to bees. For all fruitworm control applications, excellent coverage of fruit clusters is required. This can be improved by the addition of a spreader-sticker to the spray water.

After 100 percent petal fall and removal of honey bees from the field, the range of options for fruitworm control increases, with Imidan, Asana, Danitol, Mustang Max, Lannate and Sevin being some of the available broad-spectrum contact insecticides. With all these products, maintaining good coverage is still important to get residue to the parts of the berry where fruitworms are found.

Recent research trials in Michigan have demonstrated that EPA-designated Reduced-Risk insecticides Intrepid, Assail, Altacor, Exirel, Entrust and Delegate applied after petal fall can also achieve excellent control of fruitworms, with reduced negative impact on natural enemies such as parasitic waspsladybeetles and lacewings. Correct timing and coverage are critically important, so regular field scouting, using sufficient spray volume to get good fruit coverage and selecting appropriate spreader-stickers can increase activity of most insecticides applied for fruitworm control.

Be aware that this immediate post-bloom timing seems to also be the best window for controlling gall wasp infestations in susceptible blueberry fields. If that pest is present in your fields, work with your beekeeper to get the honey bee colonies removed from the farm as soon after bloom as possible. Select an insecticide that provides gall wasp and fruitworm control, and plan to make an application with Mustang Max or another pyrethroid, Lannate or Exirel as soon as the colonies are removed. Sprays targeting gall wasp will benefit from higher gallonage as well as including a penetrant to improve the insecticide’s control of this pest.

The table and figure below are designed to summarize several key factors that can help you select an insecticide for your integrated pest management program for fruitworm control in blueberries.

Details of insecticide options and timing for fruitworm control in blueberry

Compound trade name

Chemical class

Life-stage activity

Optimal spray timing

Pollinator/parasitoid toxicity rating

Imidan

 

Organophosphate

Eggs, larvae, adults

100% Petal fall

Highly toxic

Lannate/Sevin

Carbamate

Eggs, larvae, adults

100% Petal fall

Highly toxic

Asana/Danitol/

Mustang Max/Hero/Bifenture

 

Pyrethroid

Eggs, larvae, adults

100% Petal fall

Highly toxic

Exirel, Altacor

Diamide

Larvae

100% Petal fall

Relatively safe

Assail

Neonicotinoid

Eggs, larvae

100% Petal fall

Moderate toxicity

Entrust

Delegate

Spinosyn

Eggs, larvae

Early fruit set

over eggs

Moderate toxicity

Dipel

B.t.

Larvae

Early fruit set

over eggs

Relatively safe

Intrepid, Confirm

Growth regulator

Larvae

Early fruit set

over eggs

Relatively safe

Grandevo, Venerate

Biologicals

Larvae

Early fruit set

over eggs

Relatively safe

Rimon

Growth regulator

Eggs, larvae

Early fruit set

under eggs

Relatively safe

Esteem

Growth regulator

Eggs, larvae

Early fruit set

under eggs

Relatively safe

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Population emergence of fruitworm adults, eggs and larvae and the optimal timing to begin sprays of different insecticide options. Follow the label caution for bees if making applications during bloom.

Drs. Isaacs and Wise’s work is funded in part by MSU‘s AgBioResearch.

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