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Spotted Wing Drosophila Update: October 23, 2015

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David Handley, Vegetable and Small Fruit Specialist; James Dill, Pest Management Specialist; Frank Drummond, Professor of Insect Ecology/Entomology

Spotted Wing Drosophila Larva in Blackberry

SWD Larvae in Blackberry, photo by David Handley

Spotted wing drosophila populations have not shown any dramatic shifts in the past two weeks. Numbers at all sites remain at levels high enough to justify control, if any fields are still being harvested. Although there have been increases in fly populations in some sites and decreases in others, this variation is relatively small compared to populations we have seen over the past four years; and is probably not significant. What is more notable this year is the lack of a sharp increase in fly populations at the end of the season. Numbers this year are not only lower than in the past, but have remained relatively stable as the season progressed. Over the past few years we have noted a sharp increase in populations a few weeks after we start catching a significant number of flies. Whether the lack of an increase this year is due to a lower overwintering population, fewer flies coming up from the south on storm fronts, more predators and parasites, or some combination of these factors is not yet known. Hopefully, further monitoring and research will provide some answers.

Several growers have asked if they should apply a “clean-up” spray after they have finished harvesting to reduce overwintering populations of spotted wing drosophila. The short answer is “don’t bother”. Such sprays are very unlikely to have an impact on populations next year as most of the flies that come into a field very likely overwinter in another location. What may be more effective is to do a good job of pruning your plants this winter to allow more light and air movement in the planting. This will create a drier environment to discourage the flies, and improve spray penetration to make your insecticide applications more effective.

Town Spotted wing
drosophila weekly
trap catch 10/9/15
Spotted wing
drosophila weekly
trap catch 10/16/15
Spotted wing
drosophila weekly
trap catch 10/23/15
Limington 202 438 179
Limerick 840 363 165
Wells 1392 405 1196
Cape Elizabeth 233 1157 193
Bowdoinham 78 129 135
Dresden* 1743 1715 1499
Freeport 28 2
Buxton 244 262 243
Livermore Falls 57 288
Mechanic Falls 122 100 59
Poland Spring 51 39 29
Monmouth* 99 117 457
Wales 17 247 42

*Not sprayed

Spotted Wing Drosophila Trap with One Male SWD Circled

Spotted Wing Drosophila Trap, Male SWD Circled, photo by Kaytlin Woodman

David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                       Pest Management Office
P.O. Box 179                             491 College Avenue
Monmouth, ME 04259          Orono, ME 04473
207.933.2100                           1.800.287.0279

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

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