Spotted Wing Drosophila Update: 10/8/2021

Spotted Wing Drosophila Update:  10/8/2021

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


Spotted Wing Drosophila on Raspberry
SWD on Raspberry; photo by David Handley.


Spotted wing drosophila catches in vinegar/yeast traps were generally lower this week, although all locations still have fly counts well over the control threshold. Shorter day lengths and cooler temperatures are likely starting to reduce the reproductive rate of the flies. We have noticed that they are starting to develop their overwintering “morph”, that is, the flies are looking darker, larger and plumper. This is typically the type we see overwintering. However, it is also typical for the flies to keep feeding and laying eggs until the temperatures get very cold (following several frosts) and the food supply begins to run low.    So, regular sprays continue to be needed in fields that are still being harvested to prevent them 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.


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

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.


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


Other IPM Web Pages
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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 9/19/21 Spotted Wing  Drosophila weekly trap catch 9/26/21 Spotted Wing  Drosophila weekly trap catch 10/3/21
Wells 4,560 896 8,224
Limington 3,984 4,872 1,682
Limerick 2,232 2,672 1,480
New Gloucester 2,440 2,344 165
Bowdoinham 3,336 3,096 1,880
Mechanic Falls 208 215 25*
Monmouth 5,336 3,160 1,344**
Wayne 7,392 5,664 2,224

*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