Spotted Wing Drosophila Alert: 9/24/2021

Spotted Wing Drosophila Alert:  9/24/2021

David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist, Phil Fanning, Assistant Professor of Agricultural Entomology, Christina Howard, Produce Safety Professional


Male and Female Spotted Wing Drosophila Flies
Male (left) and Female (right) Spotted Wing Drosophila; photo by Griffin Dill. Actual size: 2-3 mm.

Spotted wing drosophila catches in vinegar/yeast traps have increased in most locations, with most containing fly counts in the thousands, despite regular insecticide applications. Some of this increase may be due, not only to more flies present in the fields, but also a lack of food, as harvest in some fields begins to wind down. We have found that as availability of food decreases in a field, the bait in our traps becomes more attractive to the flies and thus counts start to go up. Once the food supply is depleted, counts will finally start to go down.  At present population levels, larvae will infest any unprotected berries still in the field. Regular sprays continue to be needed to prevent fruit from becoming infested. A three to five-day spray schedule should be adequate. Rotate the insecticide products (IRAC number) used to maintain long term effectiveness.



Spotted Wing Drosophila Larvae in Raspberry
Spotted Wing Drosophila Larvae in Raspberry; photo by David Handley.


Keep fields as free as possible from over ripe fruit and waste fruit on the ground to help reduce fly numbers.  Harvest fruit regularly and often, and chill any fruit that is going to market down to 32-38 degrees Fahrenheit, to stop the development of any eggs or larvae that may be present.


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



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




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University of New Hampshire


David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                       Pest Management Unit
P.O. Box 179                            17 Godfrey Dr.
Monmouth, ME 04259           Orono, ME 04473
207.933.2100                           1.800.287.0279


Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.


The University of Maine is an equal opportunity/affirmative action institution.


Spotted Wing Drosophila Weekly Trap Captures in Yeast/Vinegar traps

Town Spotted Wing  Drosophila weekly trap catch 9/5/21 Spotted Wing  Drosophila weekly trap catch 9/12/21 Spotted Wing  Drosophila weekly trap catch 9/19/21
Wells 1,864 1,264 4,560
Limington 2,504 3,440 3,984
Limerick 115 219 2,232
New Gloucester 224 371 2,440
Bowdoinham 6,320 5,952 3,336
Mechanic Falls 154 236 208
Monmouth 11,328** 13,040** 5,336
Wayne 85* 5,482 7,392

*Trap damaged; limited data

**Unsprayed plot


Characteristics of Insecticides for Spotted Wing Drosophila Control

Trade Name IRAC Group Days to Harvest
Days of Residual
Assail® 4A 1 5-7
Mustang Max® 3 1 7
Bifenture® 3 1 (3 raspberry) 7
Brigade® 3 1 (3 raspberry) 7
Danitol® 3 3 7
Delegate® 5 3 (1 raspberry) 7
Entrust®* 5 3 (1 raspberry) 3-5
Exirel® 28 3 (1 raspberry) 5-7
Imidan® 1B 3 (not for raspberry) 5-7
Malathion 1B 1 3-5
PyGanic®* 3A 0 0
Verdepryn ® 28 1 5-7

*OMRI approved