WARNING: Spotted Wing Drosophila in TN

From David Lockwood: Spotted wing Drosophila (SWD) has been found in small fruit plantings in Tennessee.  This insect has the potential to reach high numbers very quickly and can be devastating to small fruit crops such as blueberry, blackberry and raspberry.  Damage on the fruit occurs as small, depressed, soft spots at larval feeding sites.  The presence of small maggot-like worms in containers of fruit is another indication of an infestation.

One method, suggested by Dr. Rufus Isaacs, a fruit entomologist at Michigan State Univ., to determine whether fruit might be infested with SWD involves selecting a sample of 100 berries, boiling the berries in 150 ml of water for 3 minutes and 20 seconds (one minute of actual boiling), crushing the berries over a 4-mesh per inch screen with the back of a spoon and rinsing the fruit with cold water over a dark colored tray to collect the juice and the larvae.  This provided more accurate results than manual inspection, the sugar method or the salt method.

If SWD has been found in a grower’s plantings in previous years, or if it has been found in other plantings nearby, growers should be advised to initiate a spray program as soon as possible. Applications should begin at least 2 to 3 weeks in advance of the first anticipated harvest and continue at weekly intervals throughout the harvest period. If significant rainfall occurs, reapplication of effective insecticides should be made. I am attaching an information sheet on SWD. It contains the insecticide application information contained in the Small Fruits Consortium website (www.smallfruits.org).

For organic growers, control of SWD becomes more difficult since the insecticide options are fewer. Entrust has good efficacy on SWD. It should only be used a maximum of 3 times per season. I believe the label states that is should only be used twice before rotating to another chemistry. Pyganic is less effective, but can be used in rotation with Entrust. Growers should be encouraged to use Pyganic for other blueberry insects so that Entrust can be reserved for SWD control.

Traps are available for SWD detection, but should not be used as a way to determine when to spray at this time. Ripening small fruits tend to be more attractive to SWD than the baits in traps. Therefore, once SWD starts being caught in traps there is a high likelihood that the crop may be already infested.

Once a planting becomes infested with SWD, cleaning it up becomes a problem. First, the planting should be picked clean, with all ripe fruit or close to ripe fruit being removed. Fruit should be removed from the ground under plants. Then, a spray should be applied immediately to lessen reinfestation pressures. Following this, a spray program as outlined above should be started.

Hopefully, this information will be of use to you in informing growers in your county of the proper control measures for SWD. If questions arise, please contact, Dave Lockwood or Frank Hale through: kkean@utk.edu