Sep 15, 2015

What to do about SWD-infested fruit?

The SWD monitoring network Counties are all positive for SWD as of last week, Aug. 28. A lot of SWD are being caught in traps in research sites now with population numbers expected to climb into the thousands before frost knocks them back and forces them into winter diapause.

Reports are coming in of severely infested fall raspberries. This fall will be especially challenging for fall harvest of susceptible fruits. Blackberries and raspberries are particularly vulnerable and will require intensive management with sanitation and insecticide protection. One sanitation strategy used in California for berries is for workers to crush any fruit that has fallen to the ground, reducing the chance of larvae surviving to grow into egg-laying adults. For insecticides, maintaining good coverage is essential, so keep track of rain events that can wash off insecticide (>0.5 inch) and reapply at the appropriate interval listed on the labels.

Late-season blueberries, peaches, plums and grapes are vulnerable to infestation, though not as susceptible as brambles, it will be wise to examine the crop for infestation. Fruit that is softer than it should be, with dull sunken areas and tiny drops of sap may be infested. Hold marketable fruit samples on white paper towels for a day or so and rotate it to see if it is leaking from tiny pinholes indicative of larval breathing sites. Use salt floatation to float out larvae and assess the relative abundance of larval infestation and severity of the problem. Place 50 ripe, marketable fruit in a plastic bag, cover with salt solution (1 Tbsp salt/cup water) and examine in 15-30 minutes for emerging larvae. Larvae are small 1-3 mm or 1/16-2/16 inch long. More on checking fruit for infestation is in the blog “Do my fruit have SWD?”

Infestations can contribute to sour rot in grapes and fruit decays in other fruit crops. Severely infested raspberries will appear to melt off the plants.

If fruit is still ripening and ripe fruit is infested, clean pick all ripe and overripe fruit and discard it to remove the developing SWD population from the planting. After clean picking and sanitation, apply an effective insecticide to protect the ripening fruit.

Discard infested fruit in clear plastic bags held in the sun to solarize and kill larvae or freeze it. Holding culled fruit in tightly closed plastic bags will prevent SWD adults to emerge from the infested fruit into the environment.

High temperature will dissuade SWD, but hot days this past week in NY have been followed by cool nights which has likely allowed SWD adults to escape the impact of the heat. High humidity is conducive to SWD development, so that factor will also weigh in to make management difficult this fall. The microclimate in the fruit planting can be altered with pruning practices, so plan now to prune for a more open plant canopy in 2016.

— Cornell University