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August 2012 Archives

August 15, 2012

Minnesota's Newest Fruit Pest, the Spotted Wing Drosophila

Bob Koch, Minnesota Department of Agriculture
Jeff Hahn and Eric Burkness, University of Minnesota

A new fruit pest, the spotted wing drosophila (SWD) (Drosophila suzukii), has arrived in Minnesota. This pest feeds on small fruits and stone fruits. The SWD is an invasive pest of Asian origin that was first detected in the continental United States in California in 2008 and has since spread to several western and eastern states. It was found in Minnesota in August, 2012.

The first two detections of this pest were made by members of the public who reported the flies to the Minnesota Department of Agriculture (MDA). First, a homeowner from Hennepin County contacted the MDA about some flies she found in a yeast-baited trap she placed near a raspberry patch. Days later, the MDA was contacted by a citizen who found an abundance of maggots in some wild raspberries picked in Ramsey County. The MDA quickly followed up on both of these reports to visit the sites, collect specimens and confirm the identity of this new pest. It is impressive that people noticed such a small fly (or maggot), realized that it could be a new invader, and knew to contact agricultural authorities regarding the finds. It goes to show how much people care about protecting our resources.

Bob Koch, Minn. Dept. of Ag.

Photo 1: Close up of a male spotted winged drosophila. Note the spot on the wing

The SWD looks very similar to the small fruit flies you might occasionally see flying around overripe fruit on your kitchen counter. However, unlike these other flies, which typically feed on overripe or deteriorating fruits, the SWD feeds on healthy, intact, ripening fruits. In particular, the SWD will feed on thin-skinned, soft fruits such as raspberries, blackberries, blueberries, strawberries, grapes, plums and cherries.
The SWD is difficult to distinguish from other species of small flies. The SWD is a small fly, only 2 - 3 mm (1/12 - 1/8 inch) long, with yellowish-brown coloration and prominent red eyes. Male SWD have dark spots near the tips of the clear wings. Several other species of small flies with spots on their wings can easily be confused for SWD. Female SWD have few distinguishing characters and are even more difficult to identify. Larvae of SWD are white with a cylindrical body that tapers on both ends. To date, SWD is known to be an outdoor pest; fruit flies found indoors are likely to be a different species.

Female SWD use a saw-like egg laying structure to lay their eggs in ripening fruits. The larvae of the SWD then feed within the fruits causing brown, sunken areas. Sometimes the symptoms will not show until after the crops are harvested and sometimes not until the fruits are in possession of the consumers. In addition to the damage caused directly by the larvae, the feeding makes the fruits susceptible to infestation by other insects and rot fungi and bacteria. The larvae will then leave the fruits to pupate and later emerge as adults. Multiple generations of SWD can occur in a year, with populations building throughout the summer. The overwintering stage of the SWD is the adult; however, its ability to survive Minnesota winters remains unknown.

Hannah Burrack, North Carolina State University, Bugwood.org

Photo 2: SWD damage to raspberry. Note the two larvae that just visible.

With this pest being so new to Minnesota and the United States, little is known about how big of an impact it will have and what management tactics will be most effective. The MDA will be working with the University of Minnesota (Extension and the Department of Entomology) to determine how widespread this pest is in Minnesota and to alert farmers and gardeners of its presence and potential impacts. The University of Minnesota will also be developing recommendations for management of this pest on Minnesota fruit crops. SWD could be particularly devastating to blueberry, raspberry and grape growers, but we will need more information on when the pest is active in Minnesota and how well it can survive our winter weather.

Extension programs from other states have suggested several items for consideration in management of this pest. Sanitation is an important consideration to lessen local buildup of SWD populations. Sanitation practices include frequent harvest of crop to ensure ripe fruits are not in field for extended period of time and removal and destruction of old fruit remaining on stems and fallen fruit. Furthermore, crops can be monitored with traps baited with yeast or vinegar; however, yeast-baited traps appear more effective. Traps should be checked frequently (at least weekly) to determine the presence and abundance of SWD males and females. Monitoring for activity of SWD adults is also important, because once eggs are laid in the fruits it will be too late for other management tactics (for example, insecticides) to be effective. If SWD are found in the traps, an insecticide that is registered for use in the specific crop and effective against the pest should be applied. University of Minnesota Extension is evaluating what insecticide options will be effective in Minnesota. After treatment, monitoring of SWD should continue, with additional timely treatments applied as needed.

The adult flies are difficult to distinguish from other small flies; however, if you find an abundance of small, white maggots in what were apparently healthy fruits at the time of harvest, contact the MDA's "Arrest the Pest" hotline at 1-888-545-6684 or at Arrest.the.Pest@state.mn.us.  For more information, and SWD updates, please see the University of Minnesota SWD Web page.

Look for fruit rot on pumpkins and squash




M.Grabowski, UMN Extension


Photo 1: Anthracnose fruit rot on winter squash


Michelle Grabowski, UMN Extension Educator

Although most pumpkins and winter squash are not yet ready to harvest. It is important to keep a close eye on the developing fruit. Many different kinds of fungal pathogens can rot winter squash and pumpkins before they are ripe. There are a few things that a gardener can do to prevent wide spread loss.

Weed the pumpkin patch! Weeds crowd growing fruit and create a moist shaded environment that fungal pathogens thrive in. Removing weeds from the garden allows better air flow around the developing fruit. This way the new pumpkins and squash will dry out quickly after rain or irrigation.

Remove any infected squash from the garden. Many fungal fruit rot diseases are easily splashed from one fruit to another on rain or irrigation. If one fruit is infected, the rotted area or the spots on the fruit will produce spores from now until harvest. If left in the garden, the disease will continue to spread to other developing squash and pumpkins. Infected fruit can be thrown in the compost pile if it heats up or take it to a municipal compost site.

M.Grabowski, UMN Extension

Photo 2: Butternut squash overrun with weeds

Elevate squash and pumpkins on wet heavy soils. Some fungal pathogens will infect developing pumpkins and squash from underneath, where the fruit is sitting on the soil. These bottom rots are common on heavy wet soils. Remove any squash and pumpkins that are already rotting. Elevate remaining healthy fruit on a layer of airy mulch like straw or wood chips to improve air circulation and reduce contact with soil. Be careful not to injure fruit. In the future consider growing plants on raised beds to improve drainage.

Summer 2012 Imprelis Update

Kathy Zuzek, UMN Extension Educator, Horticulture

In June, the Office of Indiana State Chemist published the 2012 Imprelis Soil and Vegetation Sampling and Analysis Follow Up Study showing 2011 and 2012 levels of aminocyclopyrachlor, the active ingredient of Imprelis, from 11 sites where Imprelis was applied. The level of aminocyclopyrachlor (ACP) was measured in both soil and vegetation. Soil samples were taken to a depth of 4 inches and were then divided into the top 2" and the bottom 2 inches. Vegetation sampled included dead spruce twigs, willow twigs, and honeylocust twigs and leaves on Imprelis-damaged trees. Levels were widely variable in both 2011 and 2012 across the 11 sites. But on average, ACP levels in the 2012 samples of were 10%, 6%, and 23% of the levels measure in 2011 for the top 2" of soil, the bottom 2" of soil, and the vegetation samples respectively.

What does this information tell us? 1) ACP levels still present in plant tissue are higher than levels in soil. 2) ACP levels are dissipating as expected according to the half-life (the time it takes for the chemical concentration to reduce by one-half) of Imprelis in turf environments. Unfortunately, there is no information available as to what the remaining ACP levels in soil and vegetation mean in terms of continuing damage or a timeframe for safe replanting in Imprelis-applied soils.

Here is what is happening to tree and shrub species on Imprelis-applied sites in MN since the last update :

Remember that the effects of Imprelis on non-target species (the injured pines, spruce, and other species growing near or in turf where Imprelis was applied as a weed killer) are the same as the effects seen on targeted weed species. ACP is a synthetic auxin or plant hormone. When applied to plants, ACP causes undifferentiated cell division and elongation in areas of new plant growth, primarily branch tips and root tips. The undifferentiated cell division and elongation results in downward bending of leaves or needles, stem thickening, severe necrosis (tissue death), stunted new growth, calloused stems and leaf veins, and crinkling, cupping and twisting of leaves, needles and stems.

K. Zuzek

Photo 1: Late bud break on Colorado spruce in July

K. Zuzek

Photo 2: Thickened shoot tips on eastern white pine

Some species like Colorado blue spruce and cottonwood had a delayed bud break and leaf out this year. Bud break on Colorado blue spruce on an Imprelis-applied site I have been observing occurred in July rather than April (Photo 1).

Among highly susceptible species like eastern white pine, Norway spruce, and white spruce that showed bud and shoot tip injury or mortality shortly after Imprelis applications in 2011, behavior is variable. Some trees continued to decline and died. Others broke bud but the new shoot tips are thickened and often have twisted needles or are completely lacking needles (Photo 2). Others are producing adventitious buds and shoots below dead stems in an effort to put on new growth. It will take time to see if these plants can be managed and restored to worthwhile landscape plants.

K. Zuzek

Photo 3: Cupped distorted foliage on honeylocust in 2012

K. Zuzek

Photo 4: Crown dieback in honeylocust

Among deciduous trees and shrubs, leaves produced in 2012 are sometimes still showing distortion, twisting, and cupping due to 2011 Imprelis applications. Honeylocust (Photo 3) and lilacs are good examples of this.


The most recent development on Imprelis-applied sites in Minnesota is on honeylocust. As has been seen in states east of Minnesota, honeylocust seems to be a particularly vulnerable deciduous tree species. Many honeylocust have died. Among those that survived, many have dieback in their crowns this year (Photo 4), a more open canopy due to reduced leaf formation, twisted and distorted foliage, and galls or tumors on the trunk (Photo 5) and throughout the tree canopy (Photo 6).

K. Zuzek

Photo 5: Honeylocust trunk galls

K. Zuzek

Photo 6: Galls in honeylocust canopy

Genista Broom Moth

Jeffrey Hahn, Asst. Extension Entomologist

An interesting caterpillar has been found apparently for the first time in Minnesota in several areas of the state. A genista broom moth caterpillar, Uresiphita reversalis, is about one inch long when fully grown. It's a pretty insect with a black head with white markings and a slender yellowish green or mustard colored body. There is a series of black and white colored tubercles (raised spots) running down its body with white hairs coming out of them.

Jeff Hahn

Photo 1: Genista broom moth caterpillar on Baptisia.

When gardeners have discovered this insect in Minnesota, it has been feeding on false indigo, Baptisia. According to BugGuide this caterpillar has also been reported to feed on Acacia, Genista, Lupinus, Texas Mountain Laurel (Sophora secundiflora) and other pea family shrubs as well as Crapemyrtle (Lagerstroemia indica) and honeysuckle (Lonicera spp.).

The adult has a conspicuous snout and holds it wings in a delta shape when at rest. The forewings are light to medium brown with several small dark spots and marking while the hind wings are yellow or orange (see the Moth Photographers Group for images and the known distribution in the U.S.).

Genista broom moths are generally distributed throughout much of the southern U.S. It has been found as close to Minnesota as Iowa and Wisconsin (which are also seeing somewhat higher than normal numbers of this moth this summer). The appearance here of this insect is likely the result of migrant moths moving into Minnesota, possibly with the help of weather patterns. A perusal of the University of Minnesota's Insect Museum emphasizes that lack of genista broom moths found in Minnesota; only nine adult moths were found in the collection and none of them are from Minnesota.

We appear to be near the end of their feeding now as larvae look like they are getting ready to pupate. If you find these caterpillars in your garden and they are about one inch long, you can ignore them as they are essentially done with their feeding. If they are smaller, you have a few options. Probably the easiest thing you can do is to handpick them. It they are numerous, consider a low impact insecticide, such as insecticidal soap, spinosad, or Bacillus thuringiensis.

It is unclear whether genista broom moths will survive winters in Minnesota. If you have discovered this caterpillar in your garden, please contact the author (hahnx002@umn.edu) and report it. We are trying to establish where these insects have been discovered and whether they are found in the same sites next summer.

August 1, 2012

Cicada Killers

Jeffrey Hahn, Asst. Extension Entomologist

Jeff Hahn

Photo 1: Cicada killer carrying a cicada back to her nest.

There have been many reports of cicada killers, Sphecius speciosus, nesting in yards, gardens, parks, and other areas. These wasps are large, 1 - 1 ½ inches long, with a black and reddish brown thorax, amber colored wings, reddish brown legs, and a black abdomen with yellow bands. They are found nesting in the soil where they prefer, well-drained, light soil exposed to full sun. A cicada killer is a solitary wasp, so you will only find one wasp per burrow. However, they are gregarious, meaning that you can find a number of them in a small area, sometimes establishing large aggregations of nests.

As their name suggests they catch cicadas. Cicadas are stout, winged insects common during the summer. However, people are more likely to hear them as they produce a power line like hum that is heard during the day. Once a cicada killer captures a cicada, she uses her stinger to paralyze it. She carries the cicada back to her nest where she will lay an egg on it. Once the grub-like larvae hatches, it feeds on the cicada. After it consumes the cicada, it pupates and remains in the burrow until next year.

Despite their size, cicada killers are not dangerous. While females have stingers, they are unaggressive and ignore people. They do not have an instinct to protect their nests (like yellowjackets and honey bees) and you can walk amongst them with little worry. Of course if you handle a cicada killer or it feels threaten, it can sting to protect itself.

Males on the other hand are territorial, looking to mate with females and chasing away other males. They can act aggressively if you enter an area they are patrolling. They will fly up to you, challenging you. Fortunately, it's all bluff as they lack a stinger and are harmless. Admittedly, that can be challenging to hold your ground when a large wasp is zooming around you but they can not hurt you.

Jeff Hahn

Photo 2: Pile of dirt in garden due tunneling by a cicada killer.

Fortunately, cicada killers are just annoying. It is possible that their tunneling can undermine patio bricks but they are not going to be more of a problem than that. If you have property where cicada killer are nesting, there are couple of options to consider. The first is to ignore them and let them run their course. Remember, there is very little risk of stings and they will go away on their by the end of the summer. However, if they enjoyed nesting there this year, there is a good chance they will return next year.

Another option is to treat the nests. Keep in mind that generally broadcast spraying the areas where they are nesting is not very effective. Instead, apply an insecticide into each individual nest entrance. Dusts are most effective, although sprays can help reduce numbers. Effective active ingredients include permethrin and carbaryl. If you have trouble finding an appropriate insecticide, contact a lawn service to treat the cicada killers for you; they have access to turf products, like those containing fipronil or deltamethrin, that home residents can not find.

Karl Foord - Extension Educator, Horticulture

I was vacationing at Scenic State Park last month, and while driving down the road to Big Fork I saw a patch of common milkweed (Asclepias syriaca) along the roadside (Photo 1). I decided to stop and see if milkweed's reputation as a butterfly magnet was truly deserved.




Karl Foord


Photo 1: Milkweed Patch



I stood in the patch for an hour. It was like being in a natural butterfly house. The amount of activity was amazing. I would estimate there to have been at least 100 butterflies in this approximately 15' x 20' patch. There was also a dizzing array of butterfly species. I have attempted to record this diversity with photographs, and using Larry Weber's Butterflies of the North Woods, have identified 26 different species.

I will divide the findings into three articles; brushfoots, skippers, and a collection of sulphurs, coppers, hairstreaks, and day-flying moths.




Karl Foord


Photo 2: Monarch Adult and Caterpillar





Karl Foord


Photo 3: Admiral and Ladies


Karl Foord

Photo 4: Great Spangled and Atlantis Fritillaries - upper wing

Karl Foord

Photo 5: Great Spangled and Atlantis Fritillaries - under wing side view




Karl Foord


Photo 6: Aphrodite Fritillary and Common Wood-Nymph


Karl Foord

Photo 7: Crescents


Karl Foord - Extension Educator, Horticulture

This is a continuation of the butterflies encountered in a roadside milkweed patch.

Karl Foord

Photo 1: Peck's and Delaware Skippers




Karl Foord


Photo 2: Silver-spotted and Least Skippers


Karl Foord

Photo 3: Long Dash and Dion Skippers




Karl Foord


Photo 4: Dun Skippers - Male and Female





Karl Foord


Photo 5: Unidentified Skipper



Karl Foord - Extension Educator, Horticulture

This is a continuation of the butterflies encountered in a roadside milkweed patch.

Karl Foord

Photo 1: Clouded and Orange Sulphurs

Karl Foord

Photo 2: Pink-edged Sulphur




Karl Foord


Photo 3: Bronze Copper and Acadian Hairstreak Butterflies





Karl Foord


Photo 4: Day-flying Moths


In conclusion, I would have to say that milkweed certainly lives up to its reputation as a butterfly magnet. I am looking for a place to establish a milkweed patch and invite the butterflies.

Deer Flies Common This Year

Jeffrey Hahn, Asst. Extension Entomologist

Deer flies (family Tabanidae) have been particularly bothersome in many areas of Minnesota this year. These flies are about 1/4 - 3/8 inch long and are stout-bodied. They have yellow or black colored bodies with dark colored markings on their wings.

Mark 'Sparky' Stensaas

Photo 1: Typical deer fly. Note the iridescent eyes.

The larvae live in aquatic or semiaquatic areas, like marshy areas, streams and ponds. Adults are found near these breeding grounds, especially along the edge of woodlands but they are strong fliers and can be found miles away from these breeding areas. Watch out for deer flies especially on sunny, calm days. They have a tendency to wait in shady areas for hosts and ambush them as they move past. Deer flies primarily use sight to find a host and seem to be particularly attracted to moving, dark shapes.

They go for the head and neck when biting people. They inflict a painful bite as they use knife-like mouthparts to slice a wound in the skin and feed on the resulting blood. Fortunately, deer flies do not vector disease in Minnesota, although some people can suffer allergic reactions to the bites. In addition to humans, these biting flies also attack many different animals, including deer, horses, and cattle. Deer flies are most common in June and July, although can persist throughout the summer.

Unfortunately, we have very limited options when it comes to preventing deer flies from biting us. It is not practical to control immature deer flies by eliminating breeding sites, i.e. marshes, streams, and ponds. There are just too many potential sites to treat and the risk of environmental harm is too great. It is also prohibitive and impractical to treat adult flies in yards, parks and others areas with insecticide applications.

Jeff Hahn

Photo 2: Deer fly taking a blood meal. Knife-like mouth parts usually results in a painful bite.

Control of deer flies usually boils down to personal protection, i.e. protective clothing, such as hats, long-sleeved shirts, and long pants to help protect exposed skin. You can also try a mosquito repellent, i.e. DEET and permethrin (follow all label directions), although the results are inconsistent.

There are also a variety of devices that purport to protect people from deer flies. One method involves placing sticky patches on the back of hats. In theory deer flies land and stick to the patch before they can bite you. Another device is the trolling deer fly trap. You use a blue cup covered with glue. You mount it either to hats or caps or machinery, such as lawn mowers.The idea is the deer flies are attracted to the cup, land and get stuck on the glue, preventing them from biting you. It is advertised to be most effective when it is moving.

Common Blight on Garden Green Beans

Michelle Grabowski, UMN Extension Educator

M. Grabowski, UMN Extension

Photo 1: Common Blight on Bean

Common blight is a bacterial disease of many kinds of bean including green beans, dry beans, and scarlet runner beans. This disease causes large brown blotches that are surrounded by a bright yellow halo on bean leaves. If disease is severe, browning of the leaves can spread, eventually killing the leaf. On bean pods, infections start as round water soaked spots, that become reddish brown with time.


Common blight is caused by the bacteria Xanthomonas campestris pv. phaseoli. Common blight bacteria often first come into the garden on infected seed. Once introduced, it can spread from plant to plant through splashing water or on a gardener's hands and tools. The bacteria can over winter in infected leaves and pods that fall to the ground. Common blight thrives in hot (82-90F) humid weather. The summer of 2012 in Minnesota has provided ideal conditions for the common blight bacteria.

Common blight is best managed by using resistant varieties. In addition, gardeners should avoid working in infected plants when they are wet. Bacteria are easily moved on hands and tools at this time. Use drip irrigation or direct water at the base of plants to avoid spreading the disease through splashing water. Remove weeds from the garden. Many weeds can harbor the bacteria. At the end of the season, remove infected plants and bring them to a municipal composting site or place them in a backyard compost that heats up. In large gardens, till under infected plant debris and avoid planting beans at that site for 2-4 years. Fungicides do not control common blight and should not be used. Although copper has been shown to be effective against some bacterial pathogens. Studies show that copper does not effectively manage common blight.

Powdery Mildew on Peonies

Michelle Grabowski, UMN Extension Educator

M.Grabowski, UMN Extension

Photo 1: Powdery Mildew on Peony

If your peonies look like they have been dusted with flour this summer, the likely culprit is powdery mildew. Powdery mildew is a fungal disease caused by Erysiphe polygoni. Several scientists have noted that powdery mildew on peony seems be an emerging problem in landscape plantings in recent years. Although powdery mildew is a common disease problem on garden plants like phlox and bee balm, many gardeners have grown peonies for decades without powdery mildew until recently.


Powdery mildew is unlikely to kill a peony plant. In fact the fungus can only feed on live plant cells. The powdery mildew fungus covers peony leaves and stems with powdery spores and fine fungal strands known as mycellia. Spores are spread from plant to plant on wind currents. In the early stages of infection, powdery mildew colonies look like fluffy snowflakes resting on the leaf surface. these infections quickly expand to cover the entire leaf surface in powdery white to gray fungal growth.

M.Grabowski, UMN Extension

Photo 2: Early infections of Powdery Mildew

Powdery mildew is more common in plants that are growing in shade and have poor air movement, as these conditions favor fungal growth. Planting peonies in full sun with good air movement around plants can help reduce problems with powdery mildew. If peonies are suffering from powdery mildew there is little that can be done this summer. Preventative fungicides can be applied when the first few leaf spots appear earlier in the year. Fungicides, however, are not necessary to protect the health of the plant and many gardeners simply choose to tolerate the white coating that shows up at the end of summer.


The amount of powdery mildew that appears often varies from year to year depending on weather conditions. So having heavily infected plants this year is no guarantee that the problem will occur to the same degree in following years. As with all leaf spot diseases, it is a good idea to remove infected plant debris from the garden to prevent overwintering of the pathogen. Infected plant debris can be brought to a municipal compost facility or composted in a backyard compost pile that heats up.

Karl Foord - Extension Educator, Horticulture

Click on the link to see the video with host Dr. Mary Meyer, Professor of Horticulture


Wild Bergamot (Monarda fistulosa)




Karl Foord


Photo 1: Wild Bergamot (Monarda fistulosa)



Compass Plant (Silphium laciniatum)

Karl Foord

Photo 2: Compass Plant (Silphium laciniatum)


Rosinweed (Silphium integrifolium)

Karl Foord

Photo 3: Rosinweed (Silphium integrifolium)


Side-oats Grama (Bouteloua curtipendula)




Karl Foord


Photo 4: Side-oats Grama (Bouteloua curtipendula)


Indian Grass (Sorghastrum nutans)




Karl Foord


Photo 5:Indian Grass (Sorghastrum nutans)



Karl Foord - Extension Educator, Horticulture

In the article Swamp Milkweed - Great for Nectar - Bizarre Flowers that appeared in the June 15 Issue of Yard and Garden News, I lamented the fact that I had no pictures of insects carrying the pollinia of milkweed.

Although the pictures in this article are of insects on common milkweed (Asclepias syracia) and not Swamp Milkweed (Asclepias incarnata) the flowers are similar enough to be applicable.

Please note the pollinia on both a native bee and a fritillary butterfly.




Karl Foord


Photo 1: Milkweed Pollinia taking a ride on a native bee





Karl Foord


Photo 2: Pollinia taking a ride on a Great Spankled Fritillary (Speyeria cybele)


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