By JEFF BURBINK
Extension Educator, Purdue Extension Elkhart County
GOSHEN — Purdue has been monitoring the population of spotted wing drosophila (SWD) across the state and the first find of the year was right here in Goshen. This non-native insect is a serious pest of soft fruits such as blackberries, raspberries, blueberries, grapes, strawberries, cherries, and peaches. It can also infest apples, apricots, and tomatoes that are damaged.
The numbers of these insects will rise rapidly over the next few days. In the heat of the summer, SWD has a life cycle of just one week, so we can assume that each week there is a new generation! Once you start finding the SWD, you must get on top of it right away.
SWD is capable of infesting healthy fruit in the field because of the presence of a knife like ovipositor that allows the female fly to cut through the skin of many soft fruit to lay her eggs inside. Most fruits become attractive for egg laying when they turn color during ripening and sugar levels increase.
On grape berries, look for small puncture wounds that may or may not be leaking juice. Cut open, peel, or smash the berry and look for larvae. The larvae are white and small, about the diameter of mechanical pencil lead (0.5 mm) and about 2 millimeters long. There may be several in each berry. In addition, look for small white larvae on the surface of berries.
On raspberry and blackberry, tease open or smash the fruit carefully and look for larvae. Any overripe or soft fruit is likely to be infested. As with grapes, there can be several larvae in each berry.
The insecticides labeled for each crop varies and growers need to pay special attention to the pre-harvest intervals (PHIs) and re-entry intervals (REIs).
To avoid pesticide resistance, avoid subjecting two consecutive generations of the insect to the same mode of action, or class of insecticide.
For example, if you sprayed your raspberries this week with Mustang Max, a pyrethroid insecticide, you would not want to spray next week with Brigade because it is also a pyrethroid. You would want to choose an insecticide from another insecticide class, such as Malathion, an organophosphate, or Delegate, a spinosyn. Ideally, in this example, I would like to see you spray a pyrethroid one week, Malathion the next week, and Delegate the following week. Then you could go back to a pyrethroid and start the rotation again.
If you choose to spray twice per week, I would recommend using the same insecticide class for both applications during a single week. Please notice that each insecticide on each crop has limits on the interval between sprays of the same product and also on the total amount of insecticide or number of sprays that can be applied. Again, note PHIs for each product on each crop. Some of those PHIs are so long that it becomes impossible to use those products during the harvest season.
Organic growers have limited insecticide choices. Entrust is effective and Pyganic is moderately effective. You are limited to 5 or 6 applications of Entrust, depending on the crop, so use those judiciously. Pyganic tends to be a knockdown product with little residual activity. It is preferable to use a lower rate of Pyganic, sprayed more frequently rather than a higher rate applied less frequently.