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Forest Pest Workshops Scheduled in SE Minnesota

Jeffrey Hahn, Extension Entomologist

Rochester will host two workshops in response to the recent discovery of emerald ash borer (EAB) in Olmsted County. The first will be a Forest Pest First Detector workshop to be held on Wednesday, November 5th from 9 AM - 3:30 PM. The cost is $40 (lunch included). In addition to EAB, other pests to be discussed include gypsy moth, Asian longhorned beetle, thousand canker disease, and Oriental bittersweet.

Jeff Hahn, Univ. of Minnesota Extension

Photo 1: Learn about emerald ash borer and other forest pests at a First Detector workshop.

The Minnesota Forest Pest First Detectors training program is designed to help identify the occurrence of Emerald Ash Borer and other forest pests in Minnesota. First Detectors are the front line of defense against likely infestations. Meeting, working with and educating the public about exotic forest pests are key activities of Forest Pest First Detectors.

Everyone is welcome to attend - even if you do not wish to become a Forest Pest First Detector! Anyone with a background in tree or forest health should consider becoming a Forest Pest First Detector.

Forest Pest First Detectors must complete online training modules before attending the one-day Forest Pest First Detector training and commit to being available and involved with the program after completing the training. Involvement includes being accessible to the public, willing to conduct site visits if necessary, report forest pest-related activities, protect confidential information, and notifying organizers of current contact information.

Visit My Minnesota Woods for more information.
To register, visit here

An Ash Management for Woodland Owners workshop is scheduled on Wednesday, November 12 from 9 AM to noon. Ash Management for Woodland Owners will include information about EAB and managing your woodland in the era of EAB. An outdoor field tour will follow an indoor presentation. This workshop is intended for woodland owners. There is a $20 fee to attend this workshop.

To register for one or both classes go to this site.

Don't Confuse Yellowjackets and Bees

Jeffrey Hahn, Extension Entomologist

Jeff Hahn, Univ of MN Extension

Photo 1: Yellowjackets are black and yellow with few hairs and construct nests made of a papery material.

As the summer winds down, people have been commonly finding insects nesting in and around their homes. There can be confusion whether people are seeing yellowjackets or honey bees. There is tendency for people to call all stinging insects "bees". This has been compounded with the recent attention in the media on honey bees so people are thinking about them even more. While yellowjackets and honey bees both can sting, they have very different biologies. At this time of the year, people are most often seeing yellowjackets.

Jeff Hahn, Univ of MN Extension

Photo 2: Honey bees are brown and black and hairy. Don't confuse them with yellowjackets.

A yellowjacket is about ½ inch long (this can vary some), black and yellow, and relatively slender with few hairs. A baldfaced hornet, actually a kind of yellowjacket, is a little larger, about 5/8th inch long, and mostly black. Honey bees are about ½ inch long brown and black, relatively slender but have more hair.

Yellowjackets construct their nests from a papery material with the combs surrounded by an envelope, while honey bees produce combs made of wax. Yellowjacket nests can be aerial, e.g. hanging from trees or attached to buildings; hidden in cavities, such as wall voids in buildings; or subterranean e.g. constructed in old rodent burrows. In cases where the nest is hidden or subterranean, a person can see the yellowjackets flying in and out of an opening but cannot see the nest.

Honey bees typically nest in artificially constructed hives. It is possible for them to nest in cavities in homes but this is not very common. While honey bees don't nest in the ground, bumble bees do. Bumble bees are stout, robust insects, usually black and yellow, and hairy. Both yellowjackets and bumble bees have annual nests, i.e. they last one year; they die when freezing temperatures arrive in the fall. However, honey bees have perennial nests which survive the winter and can live for multiple years.

Dan Martens, Univ of MN Extension

Photo 3: While people wonder if nests like this are bee hives, the papery material it is constructed from tells us this belongs to yellowjackets

It is very important to distinguish between yellowjackets and bees. If people believe they have honey bees, they may take steps to try to protect the nest or even try to have it moved despite the potential risk of stings. While it is true beekeepers can remove and relocate honey bees from a nest (if you have a confirmed honey bee nest around a home, contact the Minnesota Hobby Beekeepers Association), they do not want to and will not get involved with a yellowjacket problem. While yellowjackets are beneficial because they are important predators, they do minimal pollinating and do not need to be saved.

If you have a yellowjacket nest on your property, there are several options for dealing with it. If the nest is located a reasonably safe distance from where people may be present and the risk of stings is minimal, then just ignore it. Eventually, all of the insects in the nest die after hard frosts occur.

If a yellowjacket nest is present and you want to control it, keep a few things in mind. First, treat the nest during late evening or early morning when the yellowjackets are least active; this will help minimize the chance of stings. If after a day there is still activity, i.e. yellowjackets are still flying in and out, then repeat the treatment. If you are uncomfortable treating a yellowjacket nest, it is always an option to hire a pest management professional to deal with it; they have the experience and the appropriate tools to expertly eliminate nests.

Jeff Hahn, Univ of MN Extension

Photo 4: Yellowjacket commonly nest in the ground too!

When yellowjackets are nesting in the ground, the most effective means of controlling them is with a dust labeled for ground dwelling insects; the workers get the dust on their bodies and carry into the nest spreading it to the rest of the colony. Pouring a liquid insecticide into the nest entrance is less likely to be effective as the liquid may not reach the nest depending on where it is located within the burrow

Jeff Hahn, Univ of MN Extension

Photo 5: Hidden yellowjacket nests are tricky to control for residents; they should hire a pest management professional to do this type of job.

If you can see the nest, e.g. it is attached to the eaves, use a wasp and hornet aerosol spray and treat directly into the nest. However, yellowjacket nests that are found inside homes in wall voids, attics, concrete blocks, or similar spaces are much more challenging to control. An aerosol insecticide is not very effective. In fact, an aerosol spray can sometimes cause the yellowjackets to look for another way out, which often leads them to the inside of homes. Also, don't seal the nest opening until you know all of the yellowjackets are dead as this can cause the same reaction. It is usually best for a pest management professional to control hidden nests in buildings.

Ultimately, yellowjackets do not survive the winter. If a nest can be ignored until freezing temperatures arrive, all of the workers and the queen will die. The only survivors are the newly mated queens which have already left the nest. They will seek out sheltered sites in which to overwinter. Next spring, they will start their own nests in different sites (old nests are not reused).

Just Wait Out Foreign Grain Beetles

Jeffrey Hahn, Extension Educator

Jeff Hahn, Univ. of MN Extension

Photo 1: Don't confuse tiny foreign grain beetles for flies or fleas

Very small, brownish beetles are being found in some buildings, especially homes that have been recently constructed. Proper identification is critical as these beetles may be confused for other insects, such as fruit flies, drain flies, or fleas. A foreign grain beetle is about 1/12th inch long and reddish brown with a flattened body.

Foreign grain beetles can also fly which is why they might be confused for small-sized flies. However, foreign grain beetles have a generally harder body compared to the softer bodied flies. Fleas also have a relatively hard body but are fattened instead from to side to side; fleas are also wingless and can't fly.

The favorite food of foreign grain beetles is fungi and so they are typically found in relatively damp areas. They are often associated with new construction because the moisture in wall voids when construction is first completed in conducive for fungi which then provides a food source for the foreign grain beetles. Despite their name, foreign grain beetles are not typically found infesting food products in homes. They prefer to attack old, moldy grain products.

Fortunately foreign grain beetles are only a temporary nuisance. Adult beetles are active during late summer and early fall and then go away on their own. The beetles will survive only for one or two years in a home before it becomes too dry to support fungi and the beetles. Tolerate foreign grain beetles until they go away on their own. The best control is physical removal, e.g. with a vacuum. Insecticides do not prevent foreign grain beetles from appearing and their use is not recommended.

Click here for more information on foreign grain beetles.

EAB Found Near Rochester

Jeffrey Hahn, Extension Entomologist

Jeff Hahn, Univ. of MN Extension

Photo 1: Watch for EAB and symptoms of infested trees. In this picture is an EAB larva the S-shaped tunnels it makes.

The Minnesota Department of Agriculture (MDA) announced earlier this week that emerald ash borer (EAB) has been confirmed in Olmstead County south of Rochester. Olmstead County is now the fifth county in Minnesota to confirm EAB (Ramsey, Hennepin, Houston, and Winona counties being the others). The infestation was found near the interchange of Interstate 90 and Highway 63, about 45 miles from the nearest known EAB infestation. It is believed that EAB were accidentally moved with human assistance into this area.

Because of this infestation, Olmstead County is now under Federal and State quarantine. This quarantine restricts the movement of ash material, including branches and logs, and all hardwood firewood. More information about the EAB quarantine and regulatory restrictions can be found here.

Jeff Hahn, Univ. of MN Extension

Photo 1: The best way to slow down EAB is to NOT move firewood. Buy it where you burn it!

It is critical that residents don't move firewood, especially out of quarantined areas. Buy firewood locally from approved vendors and burn it where you buy it. By itself, EAB only travels a mile or two a year. However, when people inadvertently move infested wood, EAB can travel many miles at a time.

People can also help in the fight against EAB by being familiar with what EAB looks like and the symptoms of infested trees.  Residents should report any insects suspected to be EAB or ash trees they believe are infested with EAB to the MDA; leave a voice message at 1-888-545-6684 or e-mail Arrest.the.Pest@state.mn.us.  

More information on EAB can be found on the Extension's EAB page


Fall Webworms are Active Now

Jeffrey Hahn, Extension Entomologist

Harold Revoir

Photo 1: Fall webworms can detract from a tree's appearance but does little actual damage to it.

While most caterpillars are active during the spring, there are a few that are not feed until summer. Fall webworm caterpillars, Hyphantria cunea are first active during late July and can be found feeding into September. This caterpillar varies in color from pale green or yellow with two rows of black spots on its back with long fine white hairs.

However, an easy way to identify fall webworms is from the webbing they produce that covers the ends of branches. The caterpillars remain inside this webbing to feed on the leaves. The feed on a wide variety of hardwood trees (over 100 trees and shrubs), including black walnut, oak, birch, elm, ash, willow, cottonwood, and chokeberry.

Typically fall webworms attack large, mature trees and their feeding is minor and does not have any lasting effect on trees. Occasionally small trees are attacked; they can be severely defoliated and can even be completed encased by webs. The primary problem is to the appearance as the webbing can be unsightly. However, after fall webworms are done feeding the webbing eventually deteriorates and goes away on its own.

In the majority of cases, a fall webworm infestation can be ignored, especially if it is in a large, mature tree. Direct insecticide treatments are not effective as the webbing protects the caterpillars from sprays. It is possible to effectively spray fall webworms when the caterpillars first hatch and the webbing is still small, although people don't usually notice them then. If the webbing is within reach, it can be physically pulled out along with the caterpillars. Even if you don't get the entire webbing out, you can still knock many of the caterpillars out of the nest. Do not try to burn the webs; this is more harmful to trees than any control that is achieved.

Strawberry Root Weevils

Jeffrey Hahn, Extension Entomologist

Jeff Hahn, Univ. of Minnesota Extension

Photo 1: Strawberry root weevils are common now - don't confuse them for bed bugs

A strawberry root weevil, Otiorhynchus ovatus, is a common insect during July and August. It is small, 1/4th inch long, and dark brown to black. It is pear-shaped or light bulb-shaped with a short broad snout. It also has rows of punctures on its wing covers. A strawberry root weevil cannot fly.

As a larva, a strawberry root weevil feeds on the roots of a variety of plants, including, arborvitae, spruce, and strawberries. As an adult, it feeds on the edge of leaves. Strawberry root weevils sometimes can accidentally enter homes and other buildings. It is common to find them around sources of moistures, such as sinks and tubs. They do not cause any damage and are just a nuisance. In most cases, people see only a few weevils but there are times where homes can be plagued by large numbers of strawberry root weevils.

In addition to being a nuisance, strawberry root weevils are sometimes confused for bed bugs causing much consternation until the insect is correctly identified. A bed bug is more round in shape and lacks the snout and the punctures on its back that a strawberry root weevil possesses. It is always a good idea to have an insect correctly identified by an expert if it is suspected to be a bed bug. Strawberry root weevils are also sometimes confused as ticks because the antennae looks like a pair of legs.

Physical removal is the only necessary control. Strawberry root weevils will eventually go away on their own. For more information, see Home-invading weevils.

Watch for Masked Hunters

Jeffrey Hahn, Extension Entomologist

Jeff Hahn, Univ of Minnesota Extension

Photo 1: Masked hunter adult - they can bite if you are not careful

Some people have been encountering a 3/4 inch long, dark colored, somewhat slender insect in their homes lately. This insect is a masked hunter, Reduvius personatus, a type of assassin bug (family Reduviidae). A masked hunter is a predator, feeding on a variety of insects. It can accidentally wander into homes during summer and is considered to be just a nuisance invader. No more than a few are usually seen at a time.

Fortunately, a masked hunter is not aggressive towards people, although it is capable of inflicting a painful bite if it feels threatened. It also is not a carrier of any disease. This is important as a masked hunter has been confused with kissing bugs which do transmit Chagas disease. Chagas disease is a potentially serious illness caused by a protozoan organism.

Kissing bugs also belong to the assassin bug family which helps explain the confusion between them. However, while kissing bugs belong to the subfamily Triatominae, masked hunters are in the Reduviinae subfamily. Kissing bugs are found in South America, as well as Central America and southern Mexico and are not native to the U.S. They get their name because of their habit of biting people on the face at night.

There is not any special control for masked hunters. Physical removal is the only necessary action that needs to be taken. If possible, capture and release any found outdoors. For more information, see Masked hunters.

Hollyhock Rust at its Worst

M. Grabowski, UMN Extension

Photo 1: Hollyhock rust on leaves

Michelle Grabowski, UMN Extension Educator


Frequent rains this spring and early summer have created favorable conditions for hollyhock rust. Hollyhock rust is caused by the fungal pathogen Puccinia malvacearum, which infects hollyhocks and related weeds like roundleaf mallow (Malva neglecta).

Early symptoms of hollyhock rust are easily missed. Small waxy yellow bumps form on the lower surface of the lower leaves of the plant. With age, these pustules turn reddish brown and a bright orange spot develops on the upper leaf surface. In wet years, spores from these early infections easily spread to infect leaves, stems, petioles and even flower bracts. Heavily infected leaves turn yellow and may wither and curl. This significantly reduces the plant's ability to do photosynthesis. The hollyhock rust fungi can survive from one season to the next in infected live crowns, as spores in infected plant debris, or on seed from infected plants.

M. Grabowski, UMN Extension

Photo 2: Hollyhock rust on stem and flower bracts

Unfortunately it is too late to prevent hollyhock rust this season. Keep plants as dry as possible by avoiding sprinkler irrigation and pulling weeds to improve air circulation around the plants. This will help to reduce spread of existing infections. Gardeners with infected plants should cut off the plant at ground level after flowering is complete. Infected plant material should be removed from the garden and buried, placed in a compost pile that heats up or taken to a municipal compost facility. Next year, mulch around the base of the plant to reduce the spread of spores from plant debris. Scout plants in early spring. Look for yellow waxy pustules on the lower leaf surface. Infected leaves should be removed and buried or composted.

Pseudoscorpions are Curious, Harmless

Jeffrey Hahn, Extension Entomologist

Bunni Olson, Univ. of MN Extension

Photo 1: Pseudoscorpions look fierce but are harmless to people

A small, 1/5th inch long, reddish or brownish 'bug' with two large 'pinchers' is sometimes found in homes. Although it looks like a tick or scorpion, it is actually a pseudoscorpion. A pseudoscorpion is not an insect but is a type of arachnid, so it is related to spiders, ticks, and true scorpions. Pseudoscorpions have eight legs and pincher-like pedipalps (part of their mouthparts). They lack the stinger that true scorpions possess.

Pseudoscorpions are predators on a variety of small insects and other arthropods, like springtails, booklice, and mites. They are found in a variety of habitats, such as leaf litter, moss, and under stones and tree bark, and occasionally buildings. Despite their appearance, they are harmless to people. If you find a pseudoscorpion in your home, just physically remove it or ignore it. If possible, capture and release it outdoors. Fortunately, we rarely see more than one or two pseudoscorpions at a time. For more information, see Pseudoscorpions in homes.

Gypsy Moth Quarantine in Minnesota

Jeffrey Hahn, Extension Entomologist

(The following has been slightly modified from a June 30, 2014 news release from the Minnesota Department of Agriculture (MDA).

Bill McNee, Wisconsin Dept of Natural Resources

Photo 1: Lake and Cook counties are now under quarantine for gypsy moth

Due to the high number of gypsy moths trapped in northeast Minnesota in 2013, the Minnesota Department of Agriculture (MDA) has placed Lake and Cook counties under quarantine effective July 1, 2014.  This is the first time a quarantine for gypsy moth has been established in Minnesota.  A quarantine helps to prevent gypsy moths from being moved by human activity to uninfested counties.

Outdoor items in the quarantined counties, like logs and firewood, camping equipment and patio furniture, that could be infested with gypsy moth must be inspected and certified as gypsy moth-free before moving to a non-quarantined area. This is done in two ways:

  • Homeowners, campers and others who live in and visit the proposed quarantine will need to self-inspect outdoor household items, like RVs, camping equipment and patio furniture, before moving those items out of the quarantine.
  • A compliance agreement allows items regulated by the U.S. Department of Agriculture (USDA), including firewood, pulp wood, and saw logs, to move out of the quarantine area or to be received by a business or individual outside Lake and Cook counties. The compliance agreement outlines practices for safe handling, transportation and storage to mitigate the spread of gypsy moth. Compliance agreements are documents prepared and agreed to by the company, city, county, agency, or organization interested in moving the regulated article and the MDA, or USDA in the case of interstate movement.

The MDA has been tracking and treating gypsy moth in Minnesota for decades. Since April 2013, MDA staff has been in discussions with the timber and nursery industries, as well as local, state, federal, and tribal officials on a potential quarantine. When 2013 trapping results showed a record number of gypsy moths, 90 percent of which were located in Lake and Cook counties, an advisory group recommended a quarantine of the two northeastern most counties in the state to the Commissioner of Agriculture.

Details of the quarantine can be found at here.  For questions on gypsy moth or the quarantine, call MDA's Arrest the Pest Hotline at 888-545-6684 (voicemail) or email gypsy.moth@state.mn.us. 

Japanese Beetles Have Arrived

Jeffrey Hahn, Extension Entomologist

Japanese beetles have started showing up in gardens; the first discoveries of them were made in late June. It does not appear the late spring slowed down their emergence too much as the first week of July is about when we expect to see these beetles. It will be interesting to see how abundant they are this year. Because they were well insulated under the snow, it is not expected that last winter's cold weather had much effect on their populations.

However, a factor that does impact their relative numbers is the soil moisture at the time eggs are laid. The eggs and young white grubs are particularly susceptible to dry soil conditions. Eggs are laid soon after adults start to emerge, generally early to mid-July. However, older grubs are much more tolerant of dry soil. So the number of Japanese beetles that are present this year is related to soil moisture last summer. Although we have experienced drought in many recent years, 2013 was a fairly wet year. We could expect Japanese beetle numbers to be rebounding in at least in some areas.

Jeff Hahn, Univ. of MN Extension

Photo 1: Handpicking Japanese beetles on daily basis and putting them in soapy water can effectively reduce feeding injury on plants.

There are a variety of methods for managing Japanese beetles including physical removal. A research paper in Horticultural Entomology from this year examined the effectiveness of handpicking Japanese beetles daily on a small scale (i.e. a home landscape). This research looked particularly at the effectiveness of removing Japanese beetles at different times of the day.

The researchers found that physically removing Japanese beetles on a daily basis in general helped to significantly reduce damage on grapes compared to removing no beetles. This is because damaged leaves give off a chemical volatile which attracts Japanese beetles and increases colonization and damage to plants. Keeping numbers of Japanese beetles low helps to reduce the attractiveness of them to plants. The researchers additionally found that the best time to remove Japanese beetles is at 7:00 p.m. (compared to 8:00 a.m. and 2:00 p.m.). This is because Japanese beetle activity peaks in mid-afternoon and feeding continues overnight. Grape leaves damaged overnight were more effective in recruiting new Japanese beetles than freshly injured ones. Reducing Japanese beetles at this time was the most effective time to minimize feeding injury to plants through physical removal.

Jeff Hahn, Univ. of MN Extension

Photo 2: If you have had problems with Japanese beetle grubs, treat them preventatively now.

If you have had a problem with Japanese beetle grubs in the past, now is the best time to treat them preventatively. 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.

For those looking for a low impact approach to treating white grubs, consider parasitic nematodes, especially Heterorhabditis species. Apply nematodes late in the evening. Be sure that they are watered in and that the soil is kept moist for at least a week (two to three weeks is even better). Parasitic nematodes are available from garden catalogs or biological control companies. Milky spore disease is also a low impact insecticide; however in research trials it has not been very effective against Japanese beetle grubs.

There are several traditional preventative insecticide options that are very effective. Look for imidacloprid (various trade names) or clothianidin (Green Light Grub Control with Arena), both neonicotinoids, or chlorantraniliprole (Scott's GrubEx) a type of anthranilic diamide. If Japanese white grubs are not treated preventatively now, they can be treated curatively with Trichlorfon (Dylox) or chlorantraniliprole (Scott's GrubEx) until mid to late August. After that, the grubs are generally 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.

For more information see, Japanese beetle management in Minnesota.

Squash Vine Borers are Out Now

Jeffrey Hahn, Extension Entomologist

Jeff Hahn, Univ. of MN Extension

Photo 1: Mating squash vine borer adults

Squash vine borer adults have just been sighted. If you are growing summer squash, winter squash, or pumpkins, take the proper precautions to protect your vine crops from this insect. This garden pest less frequently attacks butternut squash, cucumbers and melons. If you are unsure whether squash vine borers are in your area, monitor your garden for their presence.

Set out a yellow pan of water. Yellow is attractive to squash vine bores, and they will fly to and fall into the water. Check these traps at least once a day. Squash vine borer adults are easy to recognize as they are wasp-like and about ½ inch long. They have an orange abdomen with black spots and the first pair of wings is metallic green while the back pair of wings is clear. These moths are active during the daytime and you may also observe them when you are in your garden.

Management of squash vine borers is often challenging. There are several steps you can take to try to minimize them, such as planting less attractive crops, making a later, second planting, using row covers (note: do not use row covers if planting vine crops in the same site in consecutive years), and well-timed insecticide treatments. For more information on squash vine borers, including management, see Squash vine borer management in home gardens

Don't be Fooled by Fungus Killed Flies

Dori Eder

Photo 1: Fungus killed flies on grape. Despite any circumstantial evidence, they are incapable of damaging plants.

People are finding a curious insect in their gardens and yards now. Grayish black flies, about ¼ inch long, are being found clinging to the leaves and stems of a variety of different plants. Their legs and wings are typically splayed out in odd, unnatural positions. If you watch the fly carefully, you will notice it doesn't move. That's because it's dead - it has been killed by a fungus that is specific to these flies.

This fungus has been particularly common this year due to the abundant rainfall we have experienced throughout much of Minnesota. When seed corn maggot flies become infected with this fungal disease, they usually fly to a plant or other object and climb up. Eventually they die, leaving their legs and wings in whatever position they were in at the time of death. Additionally, their mouthparts are often extended out. In recently infected flies, the abdomen is swollen and whitish, with fungus protruding between the body segments.

When these flies die on a plant that is damaged, it seems reasonable to blame them for this injury. However, seedcorn maggot flies do not feed on plants (in fact there are no adult flies in Minnesota that directly feed on plants). They are just a curiosity and should be ignored.

Blossom blight blasts crabapple blossoms

Michelle Grabowski, UMN Extension Educator



M. Grabowski, UMN Extension


Photo 1: Brown blossoms and leaves infected with fire blight clinging to a crabapple tree



This June, many gardeners were surprised to see the blossoms on their crabapple trees turn brown and shrivel along with the leaves growing alongside them. In many cases blossoms and leaves became discolored all along several branches (Photo 1). In other cases individual clusters were affected. A month later, these brown blossoms and leaves remain attached to the tree and are likely to stay through the growing season. These unattractive brown clumps of foliage not only affect the beauty of the tree but have a significant impact on the progression of the disease.

These unusual symptoms are caused by the disease fire blight. Fire blight is caused by the bacteria Erwinia amylovora, and it affects trees and shrubs in the Rosaceae family. Fire blight can often be found on crabapple, apple and mountain-ash in Minnesota. Serviceberry, raspberry, cotoneaster, and hawthorn are susceptible but less commonly infected.

Although blossom blight is a rare occurrence in Minnesota, fire blight is not. The fire blight bacteria can infect young green shoots and leaves in addition to blossoms. In order to start an infection, the fire blight bacteria need warm wet weather (110 degree days above 65F to be exact) and a wound or natural opening. In a typical Minnesota spring, temperatures are too cool during crabapple blossom to allow the fire blight bacteria to multiply and start an infection. When weather warms up later in the season, fire blight often infects young shoots that have been injured by insect feeding, wind whipping or other factors. This year early warm wet conditions allowed the bacteria to blight blossoms in addition to shoots.

Regardless of how the bacteria first infect the tree, once an infection has begun, the fire blight bacteria can move through the infected blossoms or shoots and into the adjoining branches. With time the bacteria can move into the main trunk and even into the roots of the tree. Infection of the trunk or roots is lethal but infection of blossoms, shoots and branches can be pruned away if caught in time.

M. Grabowski, UMN Extension

Photo 2: Purple red discoloration of bark where the fire blight infected blossoms attach indicates progression of the disease into the branch. Healthy brak of this cultivar is yellow green

Gardeners that have observed symptoms of fire blight in their crabapple trees this spring should monitor trees throughout the growing season. The extent of the progression of the disease through the tree will vary depending on the resistance level of the tree. In highly resistant trees, the infection may not progress beyond the blossoms. In less resistant trees the infection will continue into the adjoining branch causing a canker. In highly susceptible trees, the infection can progress rapidly through the branch. Home gardeners can monitor the progression of the infection by looking for purplish brown discoloration of the bark (Photo 2) and continuing death of leaves along the branch.


Infections within branches should be noted for removal during the dormant season. February and March are ideal times to prune out branches infected with fire blight because the bacteria are not active at that time. Pruning cuts should not be made during the growing season (due to risk of the pruning wound becoming infected) unless the infection is close to infecting the main trunk. This may happen if suckers or water sprouts became infected or if the tree is highly susceptible. In that case, the branch should be cut 8-10 inches below the discolored bark on a cool dry day. Pruning tools will need to be sterilized after every cut with rubbing alcohol, a 10% solution of household bleach or Lysol®. Trees infected with fire blight should not be fertilized this summer as this will promote young succulent growth that is highly susceptible to infection. More information about fire blight can be found on the UMN Extension Yard and Garden page.

Rose Chafers are Here

Cindy Schmid

Photo 1: Rose chafers on peony flowers.

Rose chafers are out in full force right now. If you live in an area with sandy soil, you are much more likely to see them in your garden. These scarab beetles feed on a variety of plants but are particularly interested in the flowers of roses and peonies. They can also feed on the leaves of a variety of plants. Rose chafers feed for about three to four weeks; we can expect to see them into early July. There are several options for dealing with this beetle including handpicking and the judicious use of insecticides. For more information, see Rose Chafers.

Cabbageworms are Active Now

Jeff Hahn, Univ. of MN Ext

Photo 1: Watch for cabbageworms on your cole crops.

Are you growing any cole crops, such as cabbage, broccoli, kale, radish, or turnip, in your garden? If you are, it's a good idea to check them out for imported cabbageworms. As an adult, imported cabbageworms are pretty white butterflies. As a caterpillar these larvae are light green with thin yellow stripes running down their body; a series of short hairs gives it a velvety appearance. It's the caterpillar stage that damages plants by chewing holes in the leaves, sometimes seriously defoliating them.

These crops can tolerate some feeding. However young seedlings and transplants are particularly susceptible to feeding injury and should be protected. Checking plants regularly is very important so any infestations can be spotted quickly to minimize injury. If any imported cabbageworms (and cabbage loopers later in the summer) are discovered, there are several options for dealing with them, including handpicking and using the low impact insecticide Bacillus thuringiensis. For more information, see Caterpillar pests of cole crops in home gardens.

Don't Confuse Sixspotted Tiger Beetles with EAB

Jeffrey Hahn, Extension Entomologist

Jeff Hahn, Univ. of MN Extension

Photo 1: Sixspotted tiger beetle, a common insect in May and June.

The sixspotted tiger beetle is a native insect found throughout most of Minnesota commonly in deciduous forests, along the edges of woods, and in adjacent fields. It can even be found in urban areas in yards and gardens. Watch for this beetle at or near the ground in areas where the sun shines.

This beetle measures about ½ inch in length. It really stands out because it is an iridescent green or blue-green. It also has six white spots, although that number can vary. The sixspotted tiger beetle has conspicuous sickle-shaped mandibles (jaws) and large bulging eyes on the side of its head.

The six-spotted tiger beetle is present in Minnesota from May into early July. It is very active, moving rapidly in short bursts. It is common to see it run rapidly or fly a short distance. As one might suspect from the large eyes and the powerful jaws, this insect is a predator on all types of insects.

Jeff Hahn, Univ. of MN Ext

Photo 1: Emerald ash borer, a slimmer and slower insect than a sixspotted tiger beetle

Besides being colorful and a fun insect to observe, a sixspotted tiger beetle is also important because people may mistake it for an emerald ash borer (EAB), a destructive invasive insect that infests and kills all species of ash. They are both a similar size and bright, iridescent green.

These two insects can be distinguished by the shape of their bodies; EAB is slender, gradually tapering to the tip of its abdomen while the wing covers of a sixspotted tiger beetle are wider than its head. Also a sixspotted tiger beetle is much faster than an EAB.  See also EAB look-a-likes.  If there is any doubt whether an insect is an EAB, capture it and take a picture and submit it to "The Arrest the Pest Line", Arrest.the.Pest@state.mn.us

Phomopsis Spruce Decline Found in Minnesota

M. Grabowski, UMN Extension



M. Grabowski, UMN Extension


Photo 1: Needle loss from Phomopsis spruce decline


A new form of an old disease has been identified in Minnesota. The fungal pathogen Phomopsis sp. has long been known to cause shoot blight on spruce trees in nurseries and tree farms. The same pathogen has now been found causing cankers, needle loss, branch death and in severe cases tree death of mature spruce trees in the landscape. This disease has been named Phomopsis spruce decline. The first case of Phomopsis spruce decline in Minnesota was identified by the University of Minnesota Plant Diagnostic Clinic this spring (May 2014).

In nurseries and on tree farms, Phomopsis shoot blight causes young needles and shoots to turn brown and curl downward. In some cases dark resinous cankers formed on young stems but damage does not commonly extend beyond that years new growth. Although this disease causes damage in nurseries and on tree farms, it has not been a common problem in landscape trees.

In recent years, Dr. Fulbright of Michigan State University has been researching decline of mature spruce trees in landscapes and on tree farms. Declining trees had discolored needles that would fall off prematurely. The buds at the tip of the branch would remain alive for awhile but eventually the branch would die. These symptoms would often progress from the bottom of the tree up into the canopy. In severe cases the tree died.

M. Grabowski, UMN Extension

Photo 2: Dark discoloration of wood caused by a Phomopsis canker

Dr. Fulbright's research led to the discovery of a new type of disease caused by an old pathogen. When bark was peeled off branches of declining spruce trees dark brown staining of the wood could be seen. These infections, called cankers, were caused by Phomopsis sp. the same fungal pathogen capable of causing shoot blight in nursery spruce trees. Since then Dr. Fulbright's research group have found Phomopsis infections associated with decline of mature spruce trees in landscapes all throughout Michigan's lower peninsula.

Many questions remain to be answered about Phomopsis spruce decline. It is unknown how or why this pathogen began infecting mature landscape trees. It is known that in nurseries the disease is significantly more severe on stressed trees. It is therefore possible that stress from environmental conditions, other pests or pathogens or other factors have played a role in the development of Phomopsis spruce decline. Several other fungal pathogens infect spruce trees in both Michigan and Minnesota. These pathogens cause needle discoloration and drop, as well as branch cankers. How all of these known pathogens interact with Phomopsis sp.is unclear. At this time there are no management recommendations for trees suffering from Phomopsis spruce decline.

While research on the biology and management of this disease continues, gardeners should do their best to reduce stress on spruce trees as well as all landscape trees. Water trees during times of drought. Mulch the area around the tree with 2-4 inches of wood chips or other organic mulch. Protect trees from damage from weed whips, lawn mowers and other equipment.

For diagnosis of spruce diseases, contact the UMN Plant Diagnostic Clinic at pdc@umn.edu or 612-625-1275.

Insects on the Loose: What's in Your Garden?

Jeffrey Hahn, Extension Entomologist

Jeff Hahn, Univ. of Minnesota Extension

Photo 1: Crucifer flea beetle and its feeding damage.

There are a variety of insects that are active now and could be in your garden. When you are inspecting your garden for pests, keep an eye out for these insects.

Flea beetles are very small, 1/16th - 1/8th inch long. They are usually dark colored although some can have red or yellow on them. An easy way to identify flea beetles is that they can jump. Flea beetles attack a variety of vegetables, including beans, broccoli, cabbage, potatoes, squash, and radish. Flea beetles chew shallow pits and small holes into leaves. This feeding can be particularly damaging to seedlings and cole crops. Go here for more information on flea beetles, including management.

Jeff Hahn, Univ. of Minnesota Extension

Photo 2: Colorado potato beetle larvae on eggplant.

Colorado potato beetles overwinter as adults and start to lay eggs in the spring. The adults are broadly oval in shape with yellowish to cream colored wing covers with ten thin black stripes. The larvae are pinkish with a humpbacked larva body. Both the adults and larvae feed on the leaves of not only potatoes but also eggplant, tomato, pepper, and similar plants. Potato tubers can be adversely affected when defoliation is severe. Go here for more information on Colorado potato beetles, including management.

Jeff Hahn, Univ. of Minnesota Extension

Photo 3: Fourlined plant bug nymph and its damage.

Also watch for fourlined plant bugs. They overwinter as eggs and emerge in the spring as small bright red immature insects (nymphs) with black wing pads. They eventually turn into yellow green insects with four black stripes. Fourlined plant bugs use their piercing - sucking mouthparts to feed on the foliage of a wide variety of plants including perennials. Their feeding causes a series of small, dark, shallow pits on the leaves. Fortunately, this feeding normally does not kill the plant although it can affect its appearance. Go here for more information in fourlined plant bugs.

European Pine Sawflies are Active Now

Jeffrey Hahn, Extension Entomologist

Do you have a pine, especially a mugo, Austrian, jack, or red pine, in your yard? Now is a good time to check it for European pine sawfly activity. These insects are caterpillar-like with black heads and gray green bodies and dark green stripes (when they are young the dark green stripes may not be visible). While they are relatively small now, they eventually will grow to be about one inch in length.

Jeff Hahn, Univ. of Minnesota Extension

Photo 1: Young European pine sawflies feeding gregariously.

Look closely for these insects as they are hard to see because they blend in so well with the needles. An advantage when inspecting for them is that they are gregarious, meaning that they occur in nonsocial groups, so there can be many feeding on a given branch (which easier to find than individual sawflies).

Your first clue that European pine sawflies are present could also be finding defoliation on branches. As feeding becomes more severe, it is usually easier to find the damage before seeing the insects. European pine sawflies feed from about mid-May through June on last year's needles. Fortunately, large trees are typically not injured, although it is possible for small trees or shrubs to be severely defoliated. There is only one generation per year.

Jeff Hahn, Univ. of Minnesota Extension

Photo 2: European pine sawfly defoliation. Note the missing needles and how some needles have turned brown and curled.

If you find European pine sawflies, first determine whether they are worth managing. If they are, there are a few options available to deal with them. First consider physically removing them. This can be done by wearing rubber gloves and running your hands up the branches, crushing the sawflies. There are several low impact insecticides that can be sprayed, especially insecticidal soap and spinosad. Keep in mind that Bacillus thuringiensis which effective against caterpillars does not kill sawflies.

Most contact, residual insecticides will work against sawflies. Because sawflies feed in groups, it is possible to spot treat infestations instead of treating entire trees. Examples of effective insecticides include permethrin, bifenthrin, and other pyrethroids, malathion, and carbaryl. Neonicotinoids, such as imidacloprid and acetamiprid, can also effectively manage sawflies. Apply imidacloprid and acetamiprid as sprays directly to the pine (Read the label directions of the specific product you intend to apply to ensure that it is used correctly).

These insecticides are hazardous to bees so don't apply them to flowering plants. Treat plants in late evening to minimize exposure to bees. 



Use caution when reading new bee and pesticide research

Jeffrey Hahn, Extension Entomologist

New research about bees and pesticides from Harvard University was recently published by Lu et al. in the Bulletin of Insectology. This research examined honey bee colonies that were fed high fructose corn syrup (HFCS) contaminated with two common neonicotinoids (imidacloprid or clothianidin) during late summer and then observed in the following spring. Both the control colonies and the insecticide exposed colonies did well going into fall. While both sets of colonies then declined, the control colony numbers rebounded while the insecticide exposed colonies suffered large losses. The authors' conclusions are that insecticides are the leading explanation for colony collapse disorder (CCD).

While this seems like compelling information on the surface, there are a number of concerns and flaws about this research that should cause readers to examine it very cautiously. The biggest concern for many is the concentration of insecticides which was fed to bees at a rate of 135.8 parts per billion (ppb), in a volume of 1.9 liters of sucrose water per colony per week, for 13 consecutive weeks. This is considered an extremely high concentration and does not represent a realistic rate of pesticide exposure to bees.

Jeffrey Hahn, University of Minnesota Extension

Photo 1: There are many factors implicated in the decline of bee health.

Interestingly, Dr Lu's own data in his 2012 research paper, also published in the Journal of Insectology, showed that at field-relevant dosages, neonicotinoids did not appear to harm bees (halfway through his research, he abruptly increased the dosage being fed to bees after it appeared that there was greater numbers of capped brood cells occurring when exposed to lower dosages).

The validity of his 2012 study is further held in question by the assumption that significant levels of residues are present in HFCS as a result of neonicotinoid seed treatment of corn, an assumption that was not tested. Eventually Dr. Lu et al. did look at this issue and in a 2013 published paper that found no neonicotinoid residues in any of the tested samples of HFCS and a maximum of 2.2 ppb of imidacloprid present in pollen. This would seem to contradict the premise used in pursuing any of this research.

Other red flags that have been raised include concern for the small sample size which did not allow for sufficient replication and does not allow for such broad conclusions that considers all geographic regions; the failure to fully explain the actual cause for the loss of one of the control colonies; and failing to thoroughly evaluate other commonly accepted stresses in CCD.

It is widely accepted that there are a variety of factors that influence bee health including parasites, diseases, loss of habitat (lack of flowers=poor nutrition), decreased genetic diversity, stresses due to beekeeper and grower practices, in hive pesticides, as well environmental pesticides. More research is needed to better determine which of these factors poses the most important threats to bee health.

Gooey Orange Fungi on Junipers

M.Grabowski, UMN Extension

Photo 1: Cedar apple rust galls on juniper

M. Grabowski, UMN Extension Educator

This time of year, several species of fungi from the genera Gymnosporangium are producing bright orange gelatinous spore producing structures on the branches of Junipers. The brilliant orange color of these fungi gives them their common name: Rust. Cedar apple rust is perhaps the most well known of the Gymnosporangium rust fungi, but here in Minnesota four different species can be found infecting junipers. Hawthorn rust, quince rust and juniper broom rust all produce similar gelatinous bright orange spore producing structures on junipers. Although these fungi can be startling to see, they rarely cause significant damage to the junipers. Spores produced in these orange gelatinous structures will not reinfect the juniper. Instead spores are carried by wind and rain to infect nearby trees and shrubs in the Rosaceae family. Each of the four Gymnosporangium rust fungi infect different members of the Rosaceae family including crabapple, serviceberry, and hawthorn. To learn more read Cedar Apple Rust and other Gymnosporangium Rusts by UMN Extension.

Andrenid Bees Are Active Now

Jeffrey Hahn, Extension Entomologist

Jeffrey Hahn, University of Minnesota Extension

Photo 1: Andrenid bee searching for its nest

Andrenid bees are common in gardens and yards now. Common species are about ½ inch long with a yellow hairy thorax and a shiny black abdomen. Andrenid bees usually overwinter as pupae and emerge as soon as the weather becomes warm. Adults are relatively short-lived, surviving about a month.

Unlike honey bees and bumble bees which are social insects, andrenid bees are solitary with just one bee living in an individual burrow. However, they are also gregarious meaning that many nests can live close together. Andrenid bees like to nest in dry, sunny sites that contain sparse vegetation. People can become concerned when they see dozens of bees flying around a small area. Fortunately, these bees are very docile and nonaggressive and stings are very rare. People who are allergic to honey bee stings are not necessarily allergic to andrenid bees.

Tolerate andrenid bees as much as possible. They are valuable pollinators and all reasonable efforts should be made to preserve them. Because they like dry sites, you may be able to discourage them by keeping an area well-watered. Gardeners may also be able to work around them by working outside during the evening when these bees are less active. Remember, that these bees are active for only about a month and then go away on their own.

Be on the watch for ticks!

Jeffrey Hahn, Extension Entomologist

Jeffrey Hahn, University of Minnesota

Photo 1: Adult female blacklegged tick. This tick is a potential vector of Lyme disease.

As the amount of time we spend outside increases, be aware that ticks are also active now. There are two common species of ticks in Minnesota, the blacklegged tick (also known as deer tick) and the American dog tick (also called wood tick). While the American dog tick is mostly a nuisance, the blacklegged tick can potentially vector diseases to people, especially Lyme disease.

Take precautions when outdoors, especially in areas where ticks are known to occur. Use repellents, especially DEET to protect against ticks. Also check yourself over carefully after being outdoors for any ticks that may have found you. Remember that a tick has to be biting to be able to transmit a disease; if it is unattached it cannot vector a disease

Jeffrey Hahn, University of Minnesota

Photo 2: Adult female American dog tick. This tick is not an important vector of disease, it is primarily a nuisance

If any ticks are found, it is important that they are correctly identified because blacklegged ticks are important disease vectors while American dog ticks are not. Color and size are not always dependable when identifying ticks and it may be necessary to have specimens identified by an expert.

Click here for more information on ticks and their control. You can also find information about tick diseases here.

Ignore ash flower galls

Jeffrey Hahn, Extension Entomologist

Jeffrey Hahn, University of Minnesota

Photo 1: Ash flower gall during early spring

At this time of year, ash flower is gall particularly conspicuous.  They are black or dark brown growths found on the branches of green ash.  Because of its unsightly appearance, some people assume that it also damages trees.  The good news is that does not affect the health of ash.  Research conducted at the University of Minnesota in the 1980's showed that the presence of galls did not impact tree health. 

Control of ash flower galls is not necessary.  It is also very difficult to obtain good management of these mites.  If treatment is attempted, try an application of dormant oil when the mites become active in spring prior to bud break (which will occur soon), although this will only be partially effective.  Ultimately the best bet is to just ignore ash flower galls.  Ash has much bigger problems with emerald ash borer being present and should be considered a low maintenance tree.

M. Grabowski, UMN Extension

Photo 1: Pagoda dogwood only partially leafed out. Dead branches were killed by golden canker.

M. Grabowski, UMN Extension Educator


Golden Canker, caused by the fungus Cryptodiaporthe corni, can easily be seen on the branches of Pagoda dogwood trees (Cornus alternifolia) this time of year. Infected branches and stems turn bright yellow with raised orange blister like spots. This diseased plant tissue clearly contrasts with the purplish green bark of a healthy Pagoda dogwood. Unfortunately branches infected with golden canker are unlikely to leaf out. The disease can continue to spread through infected branches and even into main stems. It can kill all above ground parts of the tree but will not kill the roots.

M. Grabowski, UMN Extension

Photo 2: Orange bark killed by golden canker contrasts sharply to healthy reddish purple bark.


The best time to prune out branches infected with golden canker is in March or February when fungal spores are less likely to be present to infect pruning cuts. If cold weather and deep snow prevented this from happening on time, however, branches can be pruned out on dry day. Make the pruning cut at least two buds below the visible discoloration of the bark. Be aware that in some case a canker spreads irregularly and discoloration may extend several inches longer on one side of the branch than on the other. Remove infected branches from the area. They can be burned, buried or taken to a municipal compost facility.

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