Fruitworm control in blueberries

Checking monitoring traps and weather conditions can help guide control decisions in blueberry integrated pest management.

May 15, 2018 - Author: Rufus Isaacs, and John Wise, Michigan State University Extension, Department of Entomology

It will soon be time for protecting the newly forming blueberry fruit from cherry or cranberry fruitworms. The levels of fruitworm pressure are highly variable across different farms, and many fields do not have issues with these pests. Some with light fruitworm pressure can be managed with biological or cultural controls. Parasitic wasps can be used to attack their eggs, and tillage can disrupt the overwintering cranberry fruitworm. However, in fields that have a history of economic levels of fruitworm infestation, carefully-timed application of insecticides can greatly reduce infestation by these pests.

Cherry fruitworm infest only one blueberry per larva and these are generally active a week or so earlier than cranberry fruitworm, infesting early varieties soon after fruit set. Where this moth has caused crop losses previously, the fields should be treated at 100 growing degree-days (GDD) after the first sustained moth capture. We typically count this from when you see cherry fruitworm moth captures in two consecutive checks of the traps. See below for treatment options.

As cranberry fruitworm emergence ramps up, typically during Bluecrop and Jersey bloom, check the 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 model online at Michigan State University Enviroweather for cranberry fruitworm to help identify the optimal timing for spraying to protect the small berries. This is likely to occur during bloom, and so it is very important to avoid any insecticides 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 or in the presence of pollinators have provided consistent control of fruitworms in our trials at the Trevor Nichols Research Center and at grower fields. These are the B.t. products (such as Dipel, Javelin, etc.), the bioinsecticides Grandevo and Venerate, and the insect growth regulators Intrepid and Confirm. 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, so our predicted conditions will be good for B.t. activity.

Grandevo and Venerate have demonstrated good efficacy against both fruitworm pests in trials, and both can be used in organic production systems. Intrepid is more resistant to degradation by sunlight than these other insecticides and it is much more waterproof once residues are dry, giving between seven and 14 days activity. Confirm is a similar insecticide but with slightly less activity and residual activity than Intrepid. 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, including application late in the evening after bee foraging has stopped. For all fruitworm control applications, excellent coverage of fruit clusters is required.

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, especially as the leaf canopy is expanding at this time. Research trials in Michigan have demonstrated that 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 wasps, ladybeetles and lacewings. This year we have a new insecticide option, Cormoran, which contains the same active ingredients as found in Rimon and Assail.

For all these insecticides, correct timing and coverage are critically important, so regular scouting of fields, use of 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 some reduction of gall wasp (pyrethroids, Lannate, Imidan, Exirel) and provides fruitworm control (see below), and plan to make an application as soon as the colonies are removed. Also, be aware of neighboring fields that may still be in bloom with honey bees in the fields. Sprays targeting gall wasp will also benefit greatly from much higher gallonage (60 gallons or more) as well as the inclusion of a penetrating adjuvant (e.g., horticultural oil) 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

Cormoran

Growth regulator and neonic

Eggs, larvae

100% Petal fall

Moderate toxicity

Fruitworm emergence graph

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.

Tags: agriculture, blueberries, fruit & nuts, msu extension, organic agriculture, pest management


Michigan State University Michigan State University Close Menu button Menu and Search button Open Close