Spotted wing Drosophila guidelines for management and control in berry production

Three steps to better management and control of spotted wing Drosophila in berries.

The 2012 fruit growing season is nearing conclusion almost a month ahead of previous years due to unusual climatic conditions that prevailed for most of the growing season. In addition to the problems created by spring frosts and summer drought, the presence of spotted wing Drosophila (SWD) in high numbers created serious problems for berry growers not used to dealing with such a devastating pest. Growers are still evaluating their losses. In several cases, blueberries delivered for fresh packaging or processing were rejected or downgraded and diverted for juice. In raspberries and blackberries, SWD larval infestation caused bigger problems than in blueberries, especially in fall varieties. In some instances, more than 50 percent of the entire crop was lost.

Despite these failures, Michigan’s small fruit growers are learning to deal with the threat of fruit infestations caused by the presence of SWD larvae at harvest time. So far, growers that succeeded in preventing the presence of larvae in harvested fruit followed three simple steps.

  1. Installation and monitoring of SWD traps.
  2. Timely application of control measures.
  3. Fruit inspection after each insecticide application.

So far, the most effective trapping devise for SWD is the plastic trap with the yellow sticky card inside and loaded with attracting bait made of sugar and yeast. The trap baited with this solution provided a much earlier detection of fruit fly infestations than traps baited with apple vinegar. Since no economic threshold has been established for the initiation of SWD control, insecticide applications are recommended immediately after the first flies are found in the traps. For more information on the preparation of the sugar and yeast, please read Managing spotted wing Drosophila update.

Early detection is critical to prevent the establishment of SWD in the target crop. Therefore, growers and pest consultants must check SWD traps at least twice a week to determine the appropriate timing for insecticide application. The characteristics of the SWD population dynamics, multiple generations in a short period of time, make it very difficult to determine the appropriate time for insecticide applications if traps are checked only once a week.

Verifying the effectiveness of pest control actions was critical for successful SWD management and control. Growers that inspected their berries after each insecticide application were able to manage SWD infestations while preventing unnecessary applications of insecticide (application on a calendar basis). Fruit monitoring also allowed growers to repeat the applications if failure in preventing larval infestations was observed. Submerging the berries in a salt solution is a simple and easy method to detect the presence of larvae in fresh berries after the insecticide application. For more information, please read Sampling harvested berries to detect spotted wing Drosophila larvae infestations.

We are still learning to deal with the SWD pest problem. However, the experience gained during the 2012 fruit growing season together with results from ongoing research conducted by the Michigan State University Extension Small Fruit Team will improve our understanding and ability to manage this pest. Through the knowledge acquired during this season, we will be better prepared to provide growers with more effective alternatives and strategies for the control and management of SWD during the 2013 fruit growing season.

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