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Managing SWD in blueberries

Blueberries are highly susceptible to SWD. Although early maturing varieties can escape infestation in some years, that hasn’t been the case this year in many areas of NY State. U-Pick and farm stand customers want the best from farm-fresh blueberries and SWD can mar that experience — so be proactive — make sure your customers know what you’re up against. Wholesale and processing blueberry growers know there’s zero tolerance for SWD in fruit at the retailer and processor. It’s time to learn how to protect this crop to protect your markets!

A picture showing two male SWD on a blueberry.
Two male SWD on a blueberry, photographed in early September 2013. SWD populations typically build to very high levels in late summer and early autumn.

The female SWD fruit flies can lay eggs in ripe blueberries, but also in ones that are ripening, even only pink. And because SWD has been caught at all monitoring locations across NY State, it is fair to say that the blueberry harvests currently underway are highly vulnerable to infestation.

An insecticide program is an essential component of managing SWD in blueberries; this year it will be in early-, mid-, and late-season varieties.

Things to consider regarding insecticide programs for SWD, with specific emphasis on materials registered for blueberries:

  • Population growth models for SWD calculate, theoretically, that using the most efficacious insecticide first will more successfully lower SWD numbers by knocking the population back to close to zero and delaying population growth. (This is strikingly similar to classic principles of plant disease epidemiology and tactics in plant disease management.)
  • Rotate use among insecticides with different IRAC groups -- related to the mode of action of the insecticide -- to reduce selection pressure for insecticide-resistant populations of SWD. (IRAC codes are usually given on the first page of the pesticide label near the product name. For example, Group 3A Insecticide.
  • Insecticides with probable excellent efficacy include – Delegate WG (3 days), Delegate WG supplemental label (1 day), Exirel (3 days), Bifenture 10DF (1 day), Brigade WSB 2(ee) (1 day), Danitol 2.4EC (3 days), and Mustang Maxx (1 day), Lannate SP (3 days), Lannate VP (3 days), and Imidan (3 days). Of these, choose first the one with the longest pre-harvest interval (given in parentheses) that you can accommodate; some may be out of the question at this point. Rotate to other insecticides with shorter pre-harvest intervals for closer to harvest.
  • After using a highly efficacious insecticide, for the subsequent application, it is usually adequate to use an insecticide that has lower efficacy – Entrust Naturalyte 2(ee) (3 day3), Entrust SC 2(ee) (1 day), Assail 30SG 2(ee) (1 day), Malathion 5EC 2(ee) (1 day), Malathion 8 Aquamul 2(ee) (1 day), or Malathion 57 2(ee) (1 day).
  • For organic production, Entrust Naturalyte 2(ee) (3 days) and Entrust SC 2(ee) (1 day) are the most efficacious organically-approved insecticides. Rotate this active ingredient with either Pyganic (0 days), AzaSol (0 days), Grandevo (0 days), or Venerate (0 days) along with shortening the number of days between the spray intervals.
  • The spray interval column in the Insecticide Quick Reference Guide table relates to use of the same product back-to-back. When switching to another mode of action, more frequent applications are OK and are suggested against SWD.
  • Rainfast? Research on berries has shown Mustang Maxx isn’t very rain fast, so plan to re-cover if significant rain occurs during the spray interval. This is good practice with SWD or any insecticide program if the rainfall meets or exceeds an inch of rain.
  • Don’t stretch intervals between sprays more than seven days.
  • Get excellent coverage. Spray every row (no alternate row spraying.)

Review the Quick Reference Guide to SWD Insecticides for berries at

Other tactics that can help considerably are:

Re-set blueberry fields: Because blueberries don’t all ripen at the same rate in the fruit cluster, it is possible and advisable to “re-set” the field. When fruit infestation is found via salt flotation or high numbers of SWD are caught in traps in the field, clean pick all ripe and cull fruit. Remove cull fruit from the planting and solarize it or freeze it to kill SWD. Solarize in sealed, clear plastic bags set in the sun. After clean picking, spray insecticide. Choose a material with excellent efficacy against SWD and an appropriate days-to-harvest interval.

Sanitation: Pick off and remove all cull fruit from the planting. Routine sanitation can be very beneficial in IPM – it eliminates SWD food and egg-laying resources and slows population growth. And when done routinely, it takes a lot less time and is a lot more effective. Cull fruit can be placed in clear plastic bags and left in the sun to bake or placed in a freezer to kill SWD eggs and larvae.

Mowing: Keeps the environment in the plant’s microclimate hot, sunny, and dry. On diversified farms, do be careful when timing mowing or renovation of strawberry fields so as to reduce movement of SWD from that crop into the next ripening crop on your farm. See last year’s blog on strawberry renovation,

Weed management: Keeps the environment in the plant’s microclimate hot, sunny and dry, and provides no alternate hosts. Be mindful of crops no longer being harvested. Cull fruit, unprotected with insecticide, left in those fields will provide resources for SWD population growth.

Pruning: Keeps the environment in the plant’s microclimate hot, sunny and dry, and improves spray penetration and deposition. Prune blueberries yearly. Prune shoots at the base of the plant, don’t prune out portions of shoots. Leave the best two shoots in each age category when pruning established plantings. This keep the plant balanced, growing vigorously, and fruiting well.

Cold storage: Put harvested fruit into a cooler at 32-34 F as soon as possible after harvest. Hold it there to slow and kill SWD larvae and eggs. Blueberries can tolerate 32 F storage conditions.

Consult Cornell Fruit Resources SWD Management,

Monitoring tips for SWD

Salt flotation: Routinely sample a subset of fruit that’s being harvested using salt flotation to alert you to the presence of larvae in fruit. A simple method for this is in Guidelines for Checking Fruit for SWD Larvae in the Field by Laura McDermott, Download it from the Cornell Fruit Resources SWD Monitoring page,

Two growers describe their success using salt flotation to monitor infestations in blueberries, detailed on the blog, Use salt flotation to check for SWD,

Picture of three SWD males.
Three male spotted wing Drosophila. Note the spot on each wing, which is on the end of the first vein from the outer edge of the wing.

Traps: It is relatively easy to use red or yellow sticky cards to monitor for the distinctive male SWD in fruit plantings. Set the sticky card traps on the edge of the planting where it is convenient to read them daily. Use a coffee stirrer to scrape off and discard the stuck insects daily and replace the sticky card when its stickiness has worn off. Here’s one place you can order trap and lure supplies – Great Lakes IPM,

SWD populations will 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.

So stay informed!

Comprehensive information on SWD IPM is available in Spotted Wing Drosophila IPM in Blueberries from the NE IPM Center SWD Working Group,

Consult Cornell Fruit Resources SWD Management,

Refer to the Cornell Pest Management Guidelines, and always have the latest version -- the 2019 version for Berry Crops.

For organic growers, Management Recommendations for Spotted Wing Drosophila in Organic Berry Crops,

SWD prefers nice ripe fruit — like we do! And blueberries are sooo delicious!

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