Spotted Wing Drosophila Alert and Berry Notes — July 28, 2023

David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist, Phil Fanning, Assistant Professor of Agricultural Entomology, Christina Howard, Maine New Farmer Project Manager

Spotted Wing Drosophila Larva in Raspberry
SWD Larvae in Raspberry, photo by David Handley

Spotted Wing Drosophila:

Numbers of spotted wing drosophila fruit flies caught in our traps in berry fields have increased significantly at most sites this week. Fly counts are now mostly at or above control thresholds. Sites with lower numbers (e.g. Mechanic Falls and Limington) have been spraying in recent weeks, which may account for the lower numbers. One trap in New Gloucester, placed in a raspberry planting, caught over 1000 flies this week, suggesting that populations in other sites may also see an exponential increase in numbers soon. The present conditions of warm temperatures, plenty of moisture, and lots of rotten and over ripe fruit present, are ideal for spotted wing drosophila to feed and breed, so we expect keeping this pest under control may be challenging in the coming weeks.

Regular protective sprays on any ripe berries when spotted wing drosophila flies are caught in a trap are necessary to prevent larvae from infesting the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay. At this point, a one to two week schedule of sprays should be adequate to minimize fruit infestation in fields with 10 flies or less caught per week, but once populations build to higher numbers, a 5-7 day spray schedule may be required.

For more information on identifying spotted wing drosophila (SWD) and updates on populations around the state, visit our SWD blog.

Blueberries with orange dots which is anthracnose mold spores
Anthracnose on blueberries; photo by Dr. David Handley

Berry Notes:

• Gray mold (Botrytis) fruit rot is becoming prevalent in both raspberry and blueberry plantings, due to all the wet weather, which is conducive to this fungus disease. Fungicide sprays either before or soon after a rain event can help keep this problem under control. Pristine®, Switch®, Topsin®, Captan® and Elevate® offer good control of gray mold.
• Anthracnose fruit rot continues to be a problem in blueberry fields this week. The weather has been very conducive for this fungus. Infected berries soften and collapse. Small orange dots will develop on the fruit surface, which are the spores. These will be spread onto healthy fruit through rain splashing and dripping. Pristine®, Switch® and Captan® offer good control of anthracnose.

Other IPM Web Pages
Michigan State University Spotted Wing Drosophila
Penn State University Spotted Wing Drosophila Overview
University of New Hampshire SWD Weekly IPM Reports

David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm
P.O. Box 179
Monmouth, ME 04259

Pest Management Unit
17 Godfrey Drive
Orono, ME 04473

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Weekly Spotted Wing Drosophila Trap Captures

Town Spotted Wing Drosophila weekly trap catch 7/28/23
Wells 8
Sanford 5
Limington 1
New Gloucester 1190
Mechanic Falls 1
Bowdoinham 85
Monmouth 13
Fayette 5