Will spotted wing Drosophila become a pest of saskatoon berries in 2017?

The early upswing in spotted wing Drosophila activity may lead to a new problem for Michigan’s saskatoon growers.

Laboratory studies at the Northwest Michigan Horticultural Research Center have shown spotted wing Drosophila (SWD) is capable of laying eggs and causing damage in saskatoon berries. This was a “no-choice” study, in which the adult female SWD had no other fruits to choose from. We do not know if they will lay eggs in saskatoon fruits under natural conditions. No SWD were found in extensive sampling of saskatoon fruits from an un-sprayed planting in June and July of 2016.

It could be that saskatoon berries ripen too early in the growing season to face much of a threat from SWD. In the last few years, saskatoon harvest was well underway in the first week of July, well before the mid-summer upswing of SWD populations.

The 2017 growing season may teach us some new lessons, as SWD populations have increased to significant levels earlier in the growing season, and the ripening of saskatoon berries seems to be behind the usual pace. This will result in a lot more potential for SWD to infest saskatoons.

There has been no research on appropriate pesticide choices to control SWD on saskatoons. A number of the insecticides listed for controlling other insects in the “Saskatoon Berry Pesticide Recommendations for 2017” would likely provide some level of control for SWD. Exirel, Grandevo, Danitol, Entrust and Delegate may be the best choices based on their performance against SWD in cherries.

Growers will need to be very careful about the timing of applications and the pre-harvest interval (PHI) of the products. Exirel, Danitol and Entrust have a three-day PHI; Delegate WG has a three-day PHI on the standard label, but there is now a Section 24(c) Special Local Need Label allowing a one-day PHI. Growers must possess the actual Section 24(c) label from Dow AgroSciences (No. MI-170002) to use Delegate WG in this manner.

SWD is a very challenging insect to control. ”Plan to change when dealing with spotted wing Drosophila” is an excellent Michigan State University Extension by Mark Longstroth on the many factors that are involved with controlling SWD.

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