Grand Rapids, Mich., small fruit regional report – Aug. 20, 2013

Successful control of spotted wing Drosophila at harvest time requires scouting, weather information and proper rotation of insecticides.

As of Aug. 20, 2013, the presence of spotted wing Drosophila (SWD) remains the major problem in berry production. There are several factors that may contribute to the success or failure in controlling this pest at harvest time. These factors are the monitoring program, appropriate trapping devises, access to available weather information and a good understanding of the mode of action and properties of the recommended insecticides

So far, field observations conducted since the beginning of the 2013 SWD outbreak indicate that until Aug. 12, most of the growers were doing a very good job in controlling SWD in their fields. SWD populations were low, the chemical control was effective and most of the growers were doing a good rotation of insecticides. However, more than 1.5 inches of rain that occurred on Aug. 12 around west Michigan completely changed the conditions that helped to maintain an effective pest control.

An immediate result of these weather conditions were that insecticides applied against SWD were washed-off and they lost their effectiveness to maintain SWD under control. The persistence on the crop of most recommended insecticides is severely affected by precipitations greater than 0.5 inches of rain. Growers that applied insecticides any time before the rain were caught off-guard, losing any gains made against SWD. The rain basically reset the entire IPM program and growers needed to start anew the monitoring and insecticide applications.

To complicate the situation, some of the growers experiencing problems in controlling SWD at harvest time rely on outside consulting for SWD scouting. We are observing small trapping devises made of small, plastic jars with no yellow sticky cards inside for easy SWD identification that are serviced once a week. At least in one situation the scout reported no SWD in the traps he or she was monitoring while the grower was finding large numbers of SWD in their own control traps, built according to Michigan State University Extension recommendations. Relying on inefficient traps and long scouting and trap servicing intervals (seven-day intervals) is a prefect recipe for a bad SWD control.

Finally, the most difficult issue has been the selection of the insecticide to be applied to control SWD under diverse environmental conditions. Most growers having some SWD problems rely on one or two insecticides they know well. However, new insecticides currently available for SWD control in berry production are not well-known or understood by growers. Thus, synchronizing the residual effect of the selected insecticide to the length of the harvest period is critical.

Since the harvest for both blueberries and raspberries still is going to take several weeks to be completed, we would like to provide the following recommendations:

  1. Growers need to make sure that they have the correct SWD traps. Please follow MSU Extension’s recommendation on building a SWD trap.
  2. Inspect and service SWD traps twice a week. You may request your IPM scout to provide you with timely information on the conditions of the SWD populations in your fields before you start the next harvest.
  3. Select the insecticide to be applied according to your harvest schedule. It may require applying more than one insecticide the same day. Use one insecticide with the shortest pre-harvest interval for those fields that are going to be harvested first and an insecticide with the longest pre-harvest interval for fields that will be harvested later.
  4. If rain occurs (more than 0.5 inches) any time during the following 72 hours after the application, do not think twice – repeat the application.
  5. Do NOT MIX insecticides. It may create resistance problems or outbreaks of secondary pests.

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