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Flowers, Fruits, and Frass

Local and statewide information on a variety of current topics for home gardeners and market growers.
spotted wing drosophila adult male and female and larvae  1

Update on Spotted Wing Drosophila by Aly Bronwyn

Posted by Kelly Allsup - Bugs

As blackberry and blueberry harvests are underway and peach harvest is just starting, it seems timely to re-run Dr. Weinzierl's article on Spotted Wing Drosophila monitoring and control. His article reminds growers that SWD was trapped throughout Illinois last year, and if you had them last year, you will very likelyhave them this year. If you didn't have them last year, you were lucky but you need to be diligent in monitoring this year, and be prepared to take control measures. Newsletter updates from Arkansas indicated that SWD traps had catches starting as early as May 5, 2016. A recent article written by NC State University Extension Specialist, Dr. Hannah Burrack,Preventing and Managing Spotted Wing Drosophila Infestation, discusses steps to deal with an infestation including sampling fruit, removal of ripe fruit, sanitation, post-harvest cold storage, and a continued spray program. The complete article can be found on the following link:https://entomology.ces.ncsu.edu/2016/06/preventing-and-managing-spotted-wing-drosophila-infestation/?src=rss

Bronwyn Aly (618-382-2662;baly@illinois.edu)

Update on Spotted Wing Drosophila

Yes, it's still here in 2016, and it will pose a severe threat to production of several fruit crops in Illinois for the foreseeable future. A quick review: SWD was first detected in the US in 2008. It spread rapidly throughout the country and was first recorded in Illinois in 2012. It has been "officially" recorded in counties on the northern and southern tips of the state and in counties on our eastern and western state lines ... I am nearly certain that it is present in all Illinois counties.

Adult male SWD flies have a prominent spot on each wing (hence the name), but the wings of females are not spotted. Females of this species differ from otherDrosophilaspecies by having an ovipositor (egg-laying organ) that is serrated or saw-like. This characteristic enables them to cut open the "skin" of thin-skinned fruits and lay eggs into them as they begin to ripen. Larvae (maggots) develop with fruits and can be present at harvest; we have collected as many as 50 larvae from a single raspberry that superficially appeared to be just prefect for harvest and sale. It infests a wide range of common fruit crops including blueberries, raspberries, blackberries, peaches, strawberries, cherries, and grapes. We also have reared it from mulberries, elderberries, black currents, Japanese honeysuckle, and pokeweed berries. Infested fruits appear nearly normal at first when larvae are newly hatched and just beginning to feed, but within 36 to 48 hours the fruit begins to "melt down" and collapse, and larvae become clearly visible.

If you grow blueberries, raspberries, blackberries, cherries, peaches, or grapes (or less common fruits such as mulberries, currants, or elderberries), you MUST manage this insect unless you plan to eat or sell infested fruit. Where harvest of matted-row or plasticulture strawberries ends before mid- to late June, the crop will likely escape infestation. Similarly, early blueberry varieties may ripen before infestations become common. These escapes occur because numbers of SWD that survive the winter are relatively low, and they appear to become active in mid-June to early July. Populations build up rapidly through the summer (with a little lull in the very hottest weather), and the likelihood of heavy infestations increases through fall. Researchers in the Midwest have captured adult flies in traps into December. SWD flies DO enter high tunnels and lay eggs into blackberries, raspberries, and day-neutral strawberries grown in these structures.

A key step in managing SWD is monitoring ... for adult flies and larvae in fruit:

To monitor adult SWD flies, use 1-quart cups with lures and soapy water. You can make traps or buy them ready-to-use from Great Lakes IPM. Some simple instructions for making traps ...

  • If you don't want to sort through the soapy liquid in the bottom of the trap, order some sticky yellow cards fromGreat Lakes IPM(800-235-0285). Do this first so that they arrive in the mail by the time you've completed steps 2 and 3. See page 22 of the Great Lakes IPM 2016 online catalog ... a package of 25 3" x 5" cards sells for $8.75. You will cut them in half, so 25 of them will allow you to run 5 traps for 10 weeks. Order a larger number if you need more.
  • To make traps, use 1-quart deli cups, preferably clear. (Go to a supermarket with a deli, and if they will not sell you empty containers, buy some potato salad or whatever, and save the container and lid.) Make at least 2 holes near the top of the container so that you can run wire or string through them to hang the containers. Make 8-10 more holes along the side of the container at least 2-3 inches above the bottom ... these will let flies in. The holes should be about the diameter of a number 2 pencil. Use a drill, a paper punch, or a heated metal rod to melt through the plastic. Use a paper clip or a wire to hang half of a yellow sticky card (3" x 2½") from the lid. SWD lures can be purchased fromGreat Lakes IPM(800-235-0285). Hang these lures inside the deli cups, and add about 1 inch of soapy water as a drowning agent (make by adding 1 teaspoon of borax plus one drop of unscented dish detergent to a quart of water). You can buy traps already-made if you prefer. Research is ongoing to develop an ideal lure, but the Trecé 2-part lure pictured below is the one I like best so far ... talk with Jim Hansel ofGreat Lakes IPM(800-235-0285).
  • Hang traps in the shade about waist-high in areas where ripening fruit is present. Check the traps and replace the liquid weekly. Replace the lures every 4 weeks. If you need help identifying specimens, call me or contact me by email for instructions on sending them in – Rick Weinzierl, 217-244-2126,weinzier@illinois.edu.
  • Traps provide indications of SWD population levels but do NOT necessarily provide advance warning of the need for your first spray ... in my observations here and in work in nearby states, infested fruit samples have been collected before SWD adults have been trapped in small fruit plantings. Placing a few traps in adjacent woods may increase the chance of earlier detection, but initiation of sprays or other practices should begin at fruit coloring even if traps have not yet caught SWD adults.

To determine whether or not fruit is infested, immerse a sample of harvested fruit in a fairly high concentration sugar-water solution – 1 cup granulated white sugar per 1 quart water. Within one-half hour (and in fact sooner) larvae will float to the surface. I put berries into small-mesh produce bags and place a washer (weight) on top so that the fruit remains submerged as the larvae float to the surface. The reasons to assess infestations in fruit are two-fold ... one is to determine how effective your control programs have been, and the second more critical reason is to detect infestation before you sell infested fruit to valued customers who did not want to see maggots squirming in it a day later.

So, a summary on monitoring ...

  • If SWD was present in 2015, start management with first signs of fruit coloring in susceptible crops in 2016 ... do not wait to catch SWD adults in traps.
  • Use traps baited with Trecé 2-part lures. Use yellow sticky cards and soapy water to capture flies. Lures, traps, and cards are available fromGreat Lakes IPM(800-235-0285).
  • Place some traps in adjacent woods for early detection.
  • Assess fruit infestation by immersing fruit in sugar water (1 cup granulated white sugar in 1 quart water) ... larvae will float to the surface.

To prevent infestations or at least limit losses to SWD, a combination of cultural and chemical approaches will be necessary for most growers. Clean picking and frequent picking (and removing damaged fruit) can reduce population buildups within plantings or high tunnels ... not a total solution, but valuable nonetheless. Exclusion by use of screening or fine-mesh netting has been shown to reduce infestations as well. I suspect that other suppliers also provide similar materials, but ProtekNet netting fromDubois Agrinovationis one (1-800-463-9999). In real-world settings, netting is difficult to use and generally will not completely exclude SWD flies, but in conjunction with insecticide applications to the crop, it can be beneficial (as long as it does not lead to too-high temperatures in the high tunnel or within a frame around a small number of plants).

Post-harvest chilling is also important for SWD control ... or at least for suppressing its growth in harvested fruits. Refrigeration will prevent larval growth and slow fruit breakdown.

Insecticides are needed for effective control of SWD. They should be applied to blueberries, raspberries, blackberries, and similar small fruit crops beginning at the onset of fruit coloring and ripening. Preharvest intervals (PHIs) and recommended application intervals for several insecticides are listed in the table below. Two cautions: (1) Rotate among insecticide modes of action to avoid maximum selection for insecticide resistance (particularly, do not use just Brigade, Danitol, and Mustang Max ... all are pyrethroids). (2) All of these insecticides are at least moderately toxic to bees, and in brambles and strawberries control may be necessary on ripening fruit while later blossoms are still attractive to bees. Where sprays must be applied, use liquid formulations and spray at night when bees are not foraging.

Selected insecticides for SWD control in blueberries, brambles, strawberries, and peaches.

Insecticide

PHI (days) in Blueberries

PHI (days) in Brambles

PHI (days) in Strawberries

PHI (days) in Peaches

Recommended Application Interval1,2

Brigade (bifenthrin)

1

3

0

Not labelled

5-7

Danitol (fenpropathrin)

3

3

2

3

5-7

Delegate, Radiant (spinetoram)

3

1

1

14

5-7

Entrust (OMRI) (spinosad)

3

1

1

14

3-5

Imidan (phosmet)

3

Not labeled

Not labeled

14

7

Malathion (malathion)

1

1

3

7

3-5

Mustang Max (zeta-cypermethrin)

1

1

Not labeled

14

5-7

Pyganic (OMRI) (pyrethrins)

(12 hours, REI)

(12 hours, REI )

(12 hours, REI)

(12 hours, REI)

1-2

1Interval based in part on estimates of residual activity from work done by Rufus Isaacs and in part from observations of effectiveness of spray programs in IL in 2013 and 2014.
2Reapplication of insecticides on shorter intervals is recommended following significant rainfall.

Rick Weinzierl, Weinzierl Fruit and Consulting (217-621-4957;raweinzierl@gmail.com)



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