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Spotted Wing Drosophila Update, July 31, 2020

SWD still cause for concern in ripening susceptible crops

The regional monitoring program is being conducted in berry and stone fruit crops and grapes in Essex, Chatham-Kent, Elgin, Norfolk, Halton, Oxford, Niagara, Durham and Northumberland counties.  This post provides average trap counts for all the monitored counties up to July 29, 2020.

Environment favourable for SWD development

SWD populations build rapidly when fruit is available for oviposition sites, during warm, humid, cloudy weather, and wherever crop canopies are dense and weeds are not managed or mowed. A mated female can lay about 1-3 (or more) eggs per fruit, 7-16 eggs per day, and about 350 eggs during her life span of about three weeks. During the growing season, only 10% to 15% of the total SWD population is in the adult life stage.

SWD monitoring in Ontario

SWD numbers are still elevated in Essex, Kent and Niagara. Numbers in Halton, Oxford and Northumberland increased significantly from last week.  Trap catch in Norfolk, Elgin and Durham continues to be low but consistent.

Graph of mean number of SWD/trap in monitored counties

Use these results in addition to your own monitoring program to determine when SWD is present on your farm.  Growers with ripening crops susceptible to SWD should consider using a product with activity against SWD in preharvest sprays.  Conduct a salt water test or a plastic baggie test to confirm presence of larvae in fruit.  Check the SWD product registrations on ONFRUIT at SWD Registrations 2020 – ONfruit.

The monitoring project is funded by Niagara Peninsula Fruit and Vegetable Growers Association, Ontario Grape and Wine Research and Ontario Tender Fruit Growers in collaboration with private consultants.

The following is excepted from

Factors that influence SWD control

Several factors should be considered when selecting a management strategy against spotted-wing drosophila. The level of control achieved will depend on:

  • The population structure (percent of each life stage) of the SWD population.
  • The product effectiveness.
  • The timeliness of insecticide application.
  • The coverage of the fruit with the insecticide.

Several insecticides provide adequate control of SWD, but most insecticides are effective in the field for 10 days or less. Rain or overhead irrigation wash off chemicals and limit insecticide longevity. Many Oregon growers allow up to 14 days between insecticide applications in the early spring but shorten the interval between sprays to protect late-ripening crops. As the spray interval is shortened, consider the seasonal limits for each product and the minimum time between sprays.

Insecticide efficacy varies based on SWD life stages. Malathion-based insecticide applications provide good adult control but are limited in controlling immature life stages. Spinetoram-based insecticide applications (Delegate, Entrust, Success) will kill up to 95% of adults and pupae, but affect a lower percentage of eggs and larvae.

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