Increasing Spotted Wing Drosophila

Spotted wing drosophila (SWD) activity is increasing based on positive samples from several western, southern, and central Kentucky counties. We are still collecting negative samples from some counties, including farms in the same counties where other farms have been positive for several weeks. As this pest has been detected earlier each year, we began trapping in late April, and we did get a few early captures. However, this past week we detected increased activity that is more wide spread (Figures 1 & 2). Relatively high numbers have been detected in Pulaski, Oldham, Crittenden, and Daviess counties. This increase in activity is earlier than what we have experienced in preceding years.

Figure 1. Map of sentinel locations showing first activity for 2017. Additional counties will begin sending in samples soon.

In fields we are trapping, but have not detected SWD, the risk is very low. However, even when a single SWD is trapped in fields, producers are advised to spray weekly during harvest for SWD to minimize the risk of infestation of berries. Because these crops are picked several times per week, producers are restricted to insecticides with short pre-harvest intervals (PHIs).

Figure 2. Since we began trapping in 2012, spotted wing drosophila activity has been detected earlier each year (Photo: Ric Bessin)

It is interesting that within the same county, we can have a farm where traps have been set up for several weeks but without the detection of SDW, while another farm has had relatively high levels of SDW for a few weeks. This demonstrates the value of trapping on a field-to-field basis.

Figure 3.  Our traps to monitor for SWD are made with a 1-quart deli container with two screened windows, an apple cider drowning solution, and a commercial SWD lure (Photo: Ric Bessin)

In addition to insecticidal protection of the berries when SWD is found to active in a field, immediate post-harvest cooling of picked berries is also very important to arrest the development of eggs and larvae. Home gardeners can also use fine netting to exclude SWD flies from the plantings. Nets can be draped over the plants and fixed to the ground.

For both commercial producers and home gardeners, we recommend clean harvest and removal of all ripe berries from the planting, even if those will be discarded. Culled barriers can be placed in clear plastic bags and left in the sun to kill SWD larvae or bagged and tossed in the trash.

 

Ric Bessin, Extension Entomologist

 

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