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July 2013 Archives

Spotted wing Drosophila found in Minnesota again

Jeffrey Hahn, Extension Entomologist

One of the bigger garden questions last year was whether we would see spotted wing Drosophila (SWD) again in 2013.  SWD flies are invasive insect pests that damage a variety of thin-skinned fruit crops, such as raspberries, blackberries, strawberries, cherries, plums, blueberries, and grapes.

Jeff Hahn

Photo 1: Female spotted wing Drosophila on blackberry. It lacks the dark spot on its wings that males have.

Unfortunately, the answer is yes.  The University of Minnesota and Minnesota Department of Agriculture (MDA) have detected and confirmed the presence of SWD in Minnesota this year.  The first confirmed report of SWD this year occurred on June 27 when a male SWD was found in a vineyard in Dakota County.  SWD was then verified on July 3 in summer raspberries in Rice County.  There have also been fly specimens suspected to be SWD in several other counties not only in the Twin Cities area but also in Greater Minnesota.  You can go to the MDA web page to check for updated information on where SWD has been found.  Last year, the first SWD was found in August.  Eventually, SWD was confirmed in 29 counties in Minnesota.

SWD looks very similar to the small fruit flies you might see flying around overripe fruit on your kitchen counter.  They are about 1/8th inch long, yellowish brown with red eyes.  The male is fairly easy to identify; look for a dark spot near the tip of the wing.  Unfortunately, the female lacks this spot and is difficult to identify without high magnification.  The larvae are cylindrical in shape, tapering at one end.  They are legless, whitish and very small, no more than 1/8 inch long.  However, if you find fruit fly adults or larvae associated with healthy fruit, there is a very good chance it is SWD; other fruit flies are typically associated with overripe and rotting fruit.

If you have potentially susceptible fruit in your garden, consider putting out vinegar traps to try to detect SWD so you have some warning if they are present in your garden.  If you do find SWD, be sure to harvest ripe fruit frequently.  Remove and dispose of any overripe or rotting fruits.  You can also use insecticides to help protect your fruit.  Target the adults though, as there is not any practical solution one fruit is infested by the larvae.  The only option is to properly destroy the fruit so the flies cannot finish their development.

For more information on SWD management, see the publication Spotted wing Drosophila in home gardens.

If you believe you have SWD, especially in a county where it is not been confirmed, contact the Minnesota Department of Agriculture "Arrest the Pest" hotline by email at or leave a voicemail at 1-888-545-6684. 

Karl Foord - Extension Educator, Horticulture

I just returned from a two week absence from my garden due to training and a vacation, and I was anxious to see how things had progressed.

Karl Foord

Photo 1: Leaf with holes created by leaf-cutter bees

The first thing I saw was an 'Autumn Blaze' maple volunteer on the edge of my sidewalk. Normally this would be simply a weed to pull, BUT in this case the maple leaves told an interesting story. The holes in the leaves were clearly the work of leaf-cutter bees (Megachile spp.) (photo 1). Notice that the holes cut by the bees have two different shapes. One shape is a circle (photo 2) best for plugging nesting holes, and another shape is oblong best for lining nesting holes (photo 3).

Karl Foord

Photo 2: Round holes for plugging tunnels

Karl Foord

Photo 3: Oblong holes for lining tunnels

And sure enough the leaf-cutter bee was found working a flower on Hoary Vervain (Verbena stricta) (photo 4).

Karl Foord

Photo 4: Leaf-cutter bee (Megachile spp.) on Hoary Vervain (Verbena stricta)

Also observed was an Andrenid bee on Birds-foot Trefoil (Lotus corniculatus)

Karl Foord

Photo 5: Andrenid bee on Birds-foot Trefoil (Lotus corniculatus)

Karl Foord

Photo 6: Male Widow Skimmer (Libellula luctuosa)

Karl Foord

Photo 7: Male Widow Skimmer (Libellula luctuosa) perching after having caught prey

Another fascinating creature resident in the pollinator garden was a male Widow Skimmer (Libellula luctuosa) coming in for a landing (photo 6) and perching after having caught prey (photo 7).

The garden continues to provide compelling theatre for the patient and observant. Please enjoy your garden!

Jeffrey Hahn, Extension Entomologist

Jeff Hahn

Photo 1: Spotted wing Drosophila is one of the pests attendees will learn about at the Fruit and Vegetable Pest First Detector workshop.

It is not too late to sign up for the Fruit and Vegetable Pest First Detector Workshop. If you have an interest in fruits and vegetables and want to learn more about new and emerging invasive pests and pathogens that are threatening Minnesota, then consider signing up for this half day program. This workshop, put on by the Minnesota Department of Agriculture (MDA) and the University of Minnesota Extension, is scheduled for Wednesday, July 24 at the MacMillan Auditorium at the Minnesota Landscape Arboretum. Check in starts at 8:00 a.m. and the program begins at 8:30. The workshop ends at noon.

This workshop is appropriate for anyone with an interest in fruit and vegetables, including home gardeners. Attendees will learn how to identify invasive pests and distinguish them from common look a likes. They will also find out the proper steps to take if they suspect you have found and invasive pest.

Attendees have the option to become a First Detector volunteer. First detectors are a local resource to help state officials respond to calls made to the Arrest a Pest Hotline. First Detectors are volunteers trained to help citizens diagnose and report possible infestations of invasive species to the Minnesota Department of Agriculture. First Detectors are a part of the National Plant Diagnostic Network (NPDN) First Detector Program which promotes the early detection of invasive plant pathogens, arthropods, nematodes and weeds.

For more information, see the Minnesota Fruit and Vegetable Pest First Detector web page. To register, go to the Minnesota Landscape Arboretum web page.

Ready or Not: Here come Japanese beetles!

Jeffrey Hahn, Extension Entomologist

Jeff Hahn

Photo 1: Japanese beetles were first reported in Minnesota this year on July 5.

Japanese beetles have just recently started to emerge; watch for them in your gardens and landscapes. If you find just a handful of these insects, you can easily tolerate any damage they cause. If higher numbers are found, there are steps you can take to protect your plants from them although some damage is likely to occur regardless of what you do.

Jeff Hahn

Photo 2: Japanese beetles that were handpicked off of raspberries

There are a couple of non-chemical methods you can consider. When practical, handpick the Japanese beetles from plants. This is best done early in the morning and late in the evening when Japanese beetles are less active. Have a container of soapy water with you so that beetles that are brushed or picked off the plants can end up in it where they are killed. For smaller plants, consider using a fabric barrier, like cheesecloth, around the plant. Be sure to take the fabric off of any plants that are flowering so bees can reach them.

One non-chemical method to avoid is traps. They have a floral lure attractive to both sexes and a mating pheromone that draws in just male Japanese beetles. Once deployed, traps can catch what appears to be an impressive number of insects. However, in areas where Japanese beetles are common, this is a drop in the bucket compared to what is actually present. Research from the University of Kentucky has shown that these traps actually attract more Japanese beetles than they capture; often plants in the area actually suffer more damage than without the traps.

If you are interested in using an insecticide, consider a low impact product like Neem or pyrethrins (containing PBO). However, these products are generally not very effective against large numbers of Japanese beetles. If you would like to use a product with a longer residual, consider a pyrethroid, such as permethrin, lambda cyhalothrin, or cyfluthrin. Another option is carbaryl (Sevin). Depending on the Japanese beetle numbers, you may need to make more than one application. Be careful not to apply one of these insecticides when bees are active.

Jeff Hahn

Photo 3: Don't use Japanese beetle traps. You will probably draw more beetles into your garden than what you actually catch.

Another option is the use of imidacloprid, a type of systemic insecticide (dinotefuran is a similar systemic insecticide but is less effective against Japanese beetles). It's easy to apply and is long lasting so only one application during the summer is necessary. It does not kill Japanese beetles quickly but it does cause them to stop feeding, then they die a little later. One important drawback of these products is they are very toxic to bees. Avoid treating plants, like linden and honeylocust, which are attractive to bees. It doesn't matter that the plants are not flowering at the time of application as these insecticides will be active up to a year. Another important consideration is that it takes some time for imidacloprid to be translocated in trees, up to three to four weeks for a large tree. You have to think ahead if you want to use this product.

Another option is to have your trees sprayed with chlorantraniliprole (Acelepryn). This insecticide is effective against Japanese beetles, is long lasting and has low impact on bees. It is only available to licensed applicators so you would need to contact a landscape company for this treatment.

While you're dealing with adult Japanese beetles munching on your garden and landscape plants, you might also have to worry about immature grubs in the soil feeding on the roots of turfgrass. If you experienced problems with Japanese beetle grubs last year, you can expect to have problems with them in your lawn again this year. Now is a good time to use a preventative insecticide, just as the adults are starting to become active. By the time eggs are laid and grubs hatch, about two to three weeks, the insecticide will be taken up by the grass and the young grubs will be exposed to it.

Parasitic nematodes, especially Heterorhabditis species, can be an effective, low impact treatment. Apply nematodes late in the evening. It is important that they are watered in and that the soil is kept moist for at least a week (two to three weeks is even better). Nematodes are typically mailed ordered from garden catalogs or biological control companies. Milky spore disease is a common and familiar treatment. However, it isn't very effective against Japanese beetle grubs. There are several traditional preventative insecticide options that are very effective. Look for imidacloprid (various trade names), chlorantraniliprole (Scott's GrubEx), or clothianidin (Green Light Grub Control with Arena).

Jeff Hahn

Photo 4: The smaller Japanese beetle grubs are, the easier they are to kill. By late August they will be too large to kill very easily.

As the grubs get older they are less affected by preventative insecticides. It is still possible to control them with a curative insecticide. Trichlorfon (Dylox) and chlorantraniliprole (Scott's GrubEx) are effective curative insecticides. You can effectively treat Japanese beetles until about mid to late August. By then, the grubs are getting too large to manage very well with any insecticide. Remember to only treat the grubs if you are experiencing problems in your lawn. It is not effective to control grubs to reduce the number of adults that are seeing. Adult beetles are good fliers and can easily fly into your yard from the surrounding neighborhood.

The University of Minnesota Extension and the Minnesota Department of Agriculture are conducting a survey to track where Japanese beetles are found in Minnesota. If you find Japanese beetles, contact Jeff Hahn, to report it. Please include a digital picture when you e-mail your report.

Jul1 1 2013 Issue of Yard and Garden News

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