By Sonia Schloemann, UMass Extension Fruit Program

ID/Life Cycle: Both Cranberry Fruitworm (Acrobasis vaccinia, CBFW) and Cherry Fruitworm (Grapholita packardi, CFW) are native to North America, as are the blueberries they infest. The adult forms of these fruitworms are small brownish-gray or grayish-black moths. Eggs are laid near the calyx of green fruit and are pale creamy color. Larvae found within blueberry fruit in June are small and pale yellowish or pinkish in color. CFW larvae have dark brown heads.

Photos: left, CFW adult male - MSU Blueberry Facts; next, CBFW adult male - MSU Blueberry Facts; middle, CBFW (top) and CFW (bottom) larvae - MSU Blueberry Facts; right, CBFW feeding and frass in fruit cluster - Rutgers Crop Pest Advisory.

Fruitworms overwinter as larvae in the duff around bushes or field edges and pupate in the spring, emerging as adult moths after the start of bloom and usually before early fruit set. Cherry Fruitworm (CFW) emerges earlier than Cranberry Fruitworm (CBFW). Once mated, moths move into blueberry plantings when fruit is small and green to lay eggs directly on the fruit. Larvae then tunnel into the fruit and begin feeding. Infested fruit turn prematurely blue making them easy to identify when scouting. Larvae will consume from 3-6 berries, filling them with brown frass, and web together fruit with silk. The frass from CFW remains inside the fruit whereas that from CBFW is pushed out and visible. Upon reaching maturity, larvae leave the berries and move to over-wintering sites. There is one generation per year.

Damage: Larvae feed on ripening fruit. Feeding reduces the crop and spoils marketability of the berries.

Management

Monitoring: Pheromone traps can be used to monitor male populations of these pests and helps to identify the initial flight into a blueberry planting. Lures are available for both species. Traps should be placed during bloom with a minimum 50' buffer between them. Monitor trap catches twice weekly and remove moths caught each time you check in order to identify when sustained captures occur. Secondary scouting can be done for egg laying by inspecting the calyx end of green fruit with a hand lens. Scout the periphery of the planting especially near woods and hedgerows. Finally, scout for infested fruit by looking for prematurely pigmented berries.

Developmental Model: Fruitworm development is closely related to weather conditions for both species and can be predicted with reasonable accuracy using Degree Day accumulations. Cherry Fruitworm is thought to emerge at approximately 230 GDD Base 50˚F from March 1. Cranberry Fruitworm emerges later, around 350 GDD Base 50˚F. Emergence can be confirmed by using pheromone traps that capture male moths of each species during their first flight. Noting the start of sustained trap captures can be used as the biofix for the developmental model.

The important stage to forecast for either species is egg-laying which, for CBFW, occurs during the period of 85-400 GDD Base 50˚F after the onset of sustained adult activity or flight (biofix). Therefore CBFW egg laying is generally predicted to take place during the period of 435-750 GDD Base 50˚F. Modeling for CFW egg-laying is not currently available but is likely somewhat earlier than CBFW. 

Control strategies

Cultural/Biological:

• Eliminate weeds and trash around plants to minimize protective overwintering habitat for larvae.
• Clean cultivate between rows to disrupt pupation sites and reduce the population of this pest.
• Hand pick and destroy infested fruit in small plantings.
• Preserve natural enemies whenever possible by selecting spray materials that are less toxic to beneficials.

Chemical:

• Apply recommended insecticides beginning 85 - 100 GDD base 50˚F after sustained trap catches (biofix), which usually coincide with berry-touch or when degree day models reach the action threshold.
• If action threshold is reached while some bushes are still in bloom, use materials that are listed as relatively safe for pollinators/parasitoids in chart below that are listed as relatively safe for pollinators/parasitoids.
• Avoid use of insecticides with seasonal use restrictions that may be needed for Spotted Wing Drosophila (SWD) control later in the season.
• Rotate insecticides from different IRAC groups to reduce the chance of resistance development in the pest.
• Use pesticides that are less toxic to predators (e.g., insect growth regulators or B.t. products) to promote populations of natural enemies.

Table 1. Details of insecticide options and timing for fruitworm control in blueberry as of 2016.

Trade Names***

Chemical Class

Life-stage activity

Optima 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

*** Where trade names are used, it is for the reader's information. No endorsement is implied, nor is discrimination intended against products with similar ingredients. Please consult pesticide product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

*OMRI certified for organic production.

This article was printed in the May 24th issue of the CCE ENYCHP Berry News.  To view the full newsletter click here.