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Spotted Wing Drosophila Update: August 24, 2015

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SPOTTED WING DROSOPHILA UPDATE: AUGUST 24, 2015

Click on photos to enlarge.

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

Male and Female Spotted Wing Drosophila

Male and Female Spotted Wing Drosophila, image by Alan Kenage, Capital Press

Spotted wing drosophila captures have been rising significantly in some locations this week. Although the number of flies caught has been quite variable from site to site, the significant increase in populations suggests that numbers will continue to rise as more food becomes available. Therefore, the threat of infestation to any soft fruit or berries in the field is now very high.

The highest numbers of flies were caught in traps in Limington, Buxton, Dresden, Bowdoinham and Nobleboro. Lower fly counts were found in Wells, Springvale, Limerick, Poland Spring, Monmouth and Fayette.

SWD traps should be set up in fields now, if you haven’t already. Start protective sprays on any berries that have begun to ripen once spotted wing drosophila are caught in traps, or any larvae are noticed in the fruit. Look for fruit flies hovering around fruit and symptoms of premature fruit decay.

Present warm and humid weather conditions are very good for fruit fly development; and with late fruit now ripening, abundant food will allow them to reproduce rapidly. Frequently repeated insecticide sprays (1 to 2 times per week) are often needed to prevent infestations once the insect is present in a field.

drosophila trap

Drosophila Trap, photo by David Handley

A Simple Monitoring Trap for Spotted Wing Drosophila:
The trap body is made from a 16 ounce red plastic cup (we use Solo Brand P16RLR). You’ll need one that has a tight fitting lid (we use Solo Brand 626TS). Using a 1/8” hole punch (available through art suppliers), punch about 15 holes in a row around the cup just under the lip about 1/2” apart. Leave about 2” of the diameter of the rim with no holes so that liquid can be poured in and out. Punch a second row of holes just under the first row, to give you a total of 30, 1/8” holes. Use a black permanent marker to paint a 1/2” wide black strip around the cup under the rim, right over the holes you punched. To support the trap, cut a wooden tomato stake down to about 30”. Attach a 4” or larger hose clamp near the top of the stake to act as a cup holder for the trap. (We just punched a hole in the metal band of the hose clamp and attached it to the stake with a flat-headed wood screw.) Place the trap holder in a shady, moist place in or near the fruit planting, with the cup height about 18” off the ground. Fill the trap with 4 to 6 ounces of apple cider vinegar, water + sugar + yeast, or whatever bait you prefer. It is best to add a few drops of unscented soap to break the surface tension of the liquid. Place the lid on the cup to keep rain and critters from getting in, and place the trap in the holder. Adjust the hose clamp so that the trap fits in snugly but the trap holes are not covered up. Empty and re-bait the trap every week. Do not pour out the old bait on the ground near the trap, as this will draw flies away from it.

Based on what we know so far about this pest, here again are our six rules for managing spotted wing drosophila.

  1. Monitor for the flies with traps, and for the larvae in fruit.
  2. Spray regularly and often once flies have been found in the field (1-2/week).
  3. Harvest fruit regularly and often; do not leave any ripe/rotten fruit in the field.
  4. Sort fruit at harvest; do not leave any soft fruit in the container to be sold.
  5. Chill all fruit immediately after harvest to 38ºF (or as close as you can) for at least 12 hours to slow development of any eggs or larvae.
  6. Prune the planting to open up the canopy and create dry, light conditions.

Characteristics of Insecticides for Spotted Wing Drosophila Control

Trade Name Days to Harvest
Blueberry
Days of Residual
Assail® 1 5-7
Malathion 1 5-7
Mustang Max® 1 7
Bifenture® 1 (3 raspberry) 7
Brigade® 1 (3 raspberry) 7
Danitol® 3 7
Exirel® 3 (not for raspberry) 5-7
Delegate® 3 (1 raspberry) 7
Entrust® 3 (1 raspberry) 3-5

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

Other SWD sites include:
Michigan State University’s website,
Pennsylvania State University’s SWD website, and
University of New Hampshire’s SWD web page.

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

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.

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