University of Minnesota Extension
Menu Menu

Extension > Yard and Garden News > Archives > May 2010 Archives

May 2010 Archives

Eastern Tent Caterpillars

Jeffrey Hahn, Asst. Extension Entomologist

Thumbnail image for amy freundschuh 1.JPG

Photo 1: Eastern tent caterpillars. Amy Freundschuh.

Eastern tent caterpillars have been common in many areas of Minnesota this spring. This insect is easy to identify because it constructs a silken web in the fork of branches. They attack a variety of hardwood trees, especially fruit trees, including apple, crab apple, chokecherry, cherry. These caterpillars are bluish black with yellow and a white stripe running the length of the top of its body. They are also mostly smooth except for a series of hairs sticking out along the side of their bodies. They are two inches when fully grown.

Eastern tent caterpillars normally emerge late April to early May. This year they emerged several weeks early because of the unseasonably warm weather we experienced in March and April. As a result, most, if not all of the caterpillars are fully grown and finished feeding.

The best time to treat eastern tent caterpillars is when they are half full grown length or less, i.e. no more than one inch long. An easy non-chemical method to manage eastern tent caterpillars is to wait until evening or rainy days when the caterpillars are in their webbing, then pull it out along with the caterpillars. Then destroy the insects by bagging, burning, or burying them. Insecticides are an option. Because fruit trees are typically flowering when eastern caterpillars are active, use a low impact insecticide, such as Bacillus thuringiensis, spinosad, or insecticidal soap. If caterpillars are fully grown, then just ignore them.

New Emerald Ash Borer (EAB) Fact Sheet Available

Jeffrey Hahn, Asst. Extension Entomologist

Thumbnail image for emerald ash borer 1 - Jeff Hahn.JPG

Photo 1: Emerald ash borer adult. Jeff Hahn.

A publication entitled A Guide for Homeowners on Pesticide Selection, Use, Safety, and Environmental Protection is now available. This fact sheet was written by the Minnesota Dept. of Agriculture with help from the University of Minnesota Extension and Dept. of Natural Resources. It discusses factors to consider before using an insecticide, insecticide treatment options, recommendations to protect water quality, information on insecticide labels, and how to measure trees.

A clarification should be made regarding the timing of insecticides. The included chart is generally true but it should be noted that imidacloprid should be treated in spring about 4 - 6 weeks before EAB is expected to emerge, i.e. late May or early June or the previous fall. We are at the end of the time for treatment with imidacloprid. However, the use of Tree age (emamectin benzoate) can still be used until late May to early June.

You can find this publication at the Minnesota Dept. of Agriculture web site.

Crown Gall: A bacteria at the root of the problem

Michelle Grabowski, UMN Extension Educator

cg rose FLdacs bugwood.jpg

Photo 1: Young crown gall on a rose Photo by FL dept. Ag and CS

As you purchase new plants for your garden or landscape this spring, one plant disease to look out for is crown gall. Crown gall is caused by the bacteria Agrobacterium tumefaciens. As its name implies, the crown bacteria causes a tumor like growth on the stems and roots of infected plants. Galls are round, rough textured growths. New galls are often light colored and may be smooth and slightly spongy. Older galls become hard and dry; often dark in color with many rough cracks and fissures. The most common place for galls to form is on the main stem, at the point where it enters the soil. Galls can also form on below ground roots. In some plant species, the bacteria travel through the plants vascular system and initiates rows of galls along branches.

The presence of galls on roots or the main stem of a plant may or may not affect the overall growth and productivity of the plant. Young plants with many galls and plants with a gall completely encircling the main stem are the most severely affected. Galls can restrict the flow of water and nutrients through the plant, resulting in reduced growth, low flower and fruit production, and in some cases wilting and death of leaves and stems. Plants with crown gall are more susceptible to drought stress, winter injury and secondary diseases like Armillaria root rot, that enter the plant through cracks in the gall. That being said many plants tolerate a few galls without showing any obvious above ground symptoms. Mature trees of some species have been found with many galls that appear to have little effect on the trees overall growth and productivity.

Cg on Willow G.Felt2.jpg

Photo 2: Crown gall on the trunk of a peach tree Photo by G.Felton UMN Extension.

Over 600 species of plants from over 90 different families can be infected with crown gall. This includes a wide variety of ornamental trees and shrubs, fruit trees, as well as several perennial flowers and vegetables. In Minnesota, the most commonly affected plants are roses, willow or poplar trees and fruit trees like apple, plum, cherry or apricot. All of these plants are especially susceptible to crown gall.

The crown gall bacteria are often brought into a yard or garden on infected plants or soil. A wound is necessary for the crown gall bacteria to infect a plant. Nursery activities like grafting, pruning and transplanting provide ample opportunity for the bacteria to enter and infect susceptible plant tissue. If the plant is actively growing at the time of infection, a gall can be seen in 2-4 weeks and hopefully the plant will be culled before sale. If the plant is dormant however, it may be a much longer time before the gall is visible and of course below ground galls may go completely undetected. If an infected plant is placed in the landscape, the crown gall bacteria can move into the soil and spread to other plants.

crown gall YG.jpg

Photo 3: Older crown galls on rose stem and roots Photo by M. Grabowski UMN Extension.

As galls age, they begin to break down. Layers of the gall slough off, releasing the crown gall bacteria into the soil. Crown gall bacteria can survive for a long time by living freely in the soil or in association with the roots of a wide variety of plants. Once established in an area, it can be difficult to get rid of the crown gall bacteria, so prevention is the best method of control. Be sure to inspect all new plants prior to planting them in the yard or garden. Pay especially close attention to roses, fruit trees, and poplars or willows as these are known to be highly susceptible to crown gall. Do not plant any tree or shrub with galls on the roots or stem. If crown gall is found on a recently planted tree or shrub, dig up the plant along with the soil immediately around the roots and dispose of them. Large established trees have been shown to tolerate infection with crown gall. If an established tree or shrub is found in the garden, it can be left but care should be taken to sterilize pruning tools after use on these plants. In addition presence of an infected tree indicates presence of the crown gall bacteria. Gardeners with infected trees or shrubs should avoid planting the highly susceptible trees and shrubs mentioned above.
Bob Mugaas, University of Minnesota Extension Educator

Snowmold recovery

This spring began with the very early snowmelt in mid-March that left in its wake one of the highest incidences of snow mold on many residential and commercial lawns in recent memory. Much of that could be attributed to the very wet snow that fell around Christmas time on unfrozen or barely frozen lawn surfaces. The high moisture content of the snow combined with the mostly unfrozen lawn conditions provided nearly ideal conditions for the snow mold fungi to grow and thrive. In addition, that snow cover was maintained throughout the winter months providing a very long period of total snow cover and good conditions for snow mold growth. However, as is often the case, even with as much snowmold as was evident this spring, most lawns will have recovered on their own and returned to healthy growth and good green color by early May. The severity of snowmold on some lawns did result in the need for some reseeding to fill in thin areas resulting from that injury. Photos 1 and 2 show a commercial site affected with snowmold earlier this spring that has now grown out of those symptoms without the need for reseeding or other repair. A light application of fertilizer and some watering as needed this spring will help further restore and invigorate those areas. 

Photos 1 and 2: Snowmold infestation and turf recovery. Bob Mugaas

snowmold before and after.jpg

Meadow vole damage and recovery

That continuous snow cover over winter also created a good habitat for meadow voles to invade our lawns resulting in slight to extensive surface tunneling in lawns, especially those close to unmaintained grassy areas such as next to vacant lots, prairie edges or other nearby grassy areas where voles retreat to after the snow melts. See Photo 3 for typical injury associated with meadow voles in lawns. For the most part, these critters tunnel along the surface eating a variety of vegetative material including the grass. One may observe tunnels traveling over and through the lawn surface. It is often common to see loose grass 'clippings' mounded up over the tunnels creating a slightly raised appearance to the seemingly random tunnel patterns. While the grass foliage is eaten by the voles, the grass plant crowns (growing points) often escape being eaten and are responsible for the regeneration of new leaves and stems that ultimately fill in the tunneled areas. Since the plant is having to start from scratch in its spring regrowth, the tunneled areas frequently lag behind the rest of the lawn area in spring recovery but do ultimately catch up to the rest of lawn in terms of height and density. See Photo 4 of new grass shoots coming in a surface tunnel caused by voles. Again, a light application of fertilizer and water as needed will help restore the growth and vigor of these areas. In nearly all cases, recovery occurs without the need for reseeding or replacing the damaged areas.

Photos 3 and 4: Vole damage and indications of turf recovery. Bob Mugaas.


Early season mowing

Picture 5.JPG

Photo 5: Turfgrass color variances associated with differing heights of growth prior to first mowing. Bob Mugaas.

By the writing of this article most of us have had to mow our lawns at least once or even twice already this season. In some cases, there appears to be areas of yellow or lighter green grass following mowing, especially the very first mowing of the year. See Photo 5. With the typical unevenness of that very early spring growth prior to the first mowing, it's not uncommon to see lighter areas intermingled with normal darker green areas. The lighter areas are usually associated with grass that had grown vigorously early and was taller than much of the surrounding grass. Hence, when its mowed at regular mowing heights, the grass ends up being cut back into lower blade and sheath tissue which is often lighter green to almost yellow due to the lack of chlorophyll. Cutting into that area of the plant is very stressful for the grass plant as it eliminates much of the leaf surface responsible for making the plant's food and can slow or even stop root growth temporarily until the plant can regrow sufficient tissue to resume normal growth. Grass that has not grown so vigorously or just grown more slowly ends up not being cut back so severely and hence retains its normal medium to dark green color and relatively uninterrupted growth. In most instances these early growth differences even out by the third or fourth mowing. Mowing higher rather than shorter, especially for the first cutting or two may help avoid cutting those taller areas too short initially while still being fine for the rest of the lawn area. This will also avoid the generation of excessively long and large amounts of clippings as also seen in Photo 5. When this quantity of clippings is generated from mowing, they should be removed or at least more uniformly dispersed over the lawn surface so as not to remain in large clumps, which can interfere with the healthy growth of grass plants underneath the clumps.

Crabgrass arrives early too!

Picture 6.JPG

Photo 6: Crabgrass seedlings visible April 20, 2010 near a curbline in North St. Paul, MN. Bob Mugaas.

By the middle of April, crabgrass seedlings were already emerging in what are termed heat sink areas. These are areas that warm more quickly during the early part of the growing season and hence growth in these areas is usually well ahead of the majority of the main lawn areas. Examples include areas next to sidewalks, driveways, curbs, narrow boulevards, unprotected bare soil areas and the like. Usually the warming effect extends less than two feet from these paved areas back into the main lawn. Other exposed soil areas, especially those with south and west exposures generally warm more quickly than those covered with some form or vegetation or mulch. In addition, sandy soils tend to warm more quickly than heavier clay soils. Since drier soils are warmer soils compared to moist soils, the lack of early spring precipitation over much of the area caused soils to dry more quickly with the above average temperatures and sunlight. This also contributed to warmer than usual soils that in turn saw some of the earliest crabgrass germination in quite some time in the Twin Cities area. See Photo 6 of newly emerged crabgrass seedlings near a curb area.

Once crabgrass has emerged from the ground and is visible, it is too late to apply preemergence herbicides for crabgrass control. These products act on the newly germinating crabgrass seedlings prior to their emergence from the ground. In this case, one will need to use products containing the active ingredients quinclorac or fenoxaprop-p-ethyl. Both of these are available through commercial lawn care firms. Quinclorac can also be found in some homeowner lawn weed control formulations. Check the product label for its list of active ingredients. For very small infestations, it may be practical to manually remove them. In either case, treating the seedlings while they are still small and tender is much more effective than when plants are larger and more mature.

Just because you may have already observed some crabgrass germination in those heat sink areas, it doesn't necessarily mean you shouldn't apply a preemergent crabgrass control product to the rest of the lawn area if it's needed. However, it should be applied very soon, like within the first week or so of May, depending on your specific site conditions. Soil temperatures in the main lawn areas will lag behind those in heat sink areas, but they do catch up fairly quickly as temperatures continue to warm, especially overnight temperatures. Even though crabgrass germinates earlier in those warmer soils, it doesn't germinate all at once. Hence, an application of preemergence herbicide in those heat sink areas can help prevent later germinating seeds from getting started but won't kill those already sprouted.

Easy-does-it for spring fertilizing

Usually about the time the lawn is greening up and in need of its first mowing is a good time to consider applying a spring application of lawn fertilizer. For many of us, that time may have already passed. However, that doesn't mean it's too late to fertilize the lawn. In fact, sometime within the first three to four mowings of the year is still a good time to fertilize. Regardless of the situation, it's wise to not be aggressively fertilizing your lawn in the spring, especially with large amounts of nitrogen. That's best left for the late summer period.

In the spring, there is a natural, normal flush of growth by our grass plants. It begins with active root growth followed by rapid shoot growth. As shoot growth begins to accelerate, root growth tends to slow down. If too much nitrogen fertilizer is applied, shoot growth will be even more rapid resulting in a more frequent need for mowing but is also unhealthier for the grass plant. Excessive growth stimulated by too much nitrogen creates a more succulent plant that in turn requires greater amounts of moisture to sustain its growth. That increased succulence is more vulnerable to injury from summertime stresses and can be more prone to certain disease and insect infestation. The bottom line is, use moderate to low amounts of N in the spring to maintain balanced, but healthy, turfgrass growth. For more information on lawn fertilizing, see the publication Fertilizing Lawns (

Water if needed to support early season growth

While we often don't think of watering our lawns much before sometime in May, this year, due to the drier than normal conditions and earlier than normal vigorous grass growth, watering may be needed to sustain healthy, early season turfgrass growth. Early spring is the time of year when grass plants are actively growing new and deeper roots. That allows the plant to mine water and nutrient reserves from a larger soil volume, which, in turn, sustains the continued healthy growth of new shoots and roots. At this time of year watering deeply but infrequently is a good practice. Thus, an inch of water per week (or longer interval depending on weather conditions) including any rainfall that occurs will help keep soils moist and promote healthy root growth. If you have heavier, more clay-like soils where it takes a long time for water to infiltrate into the soil, it's usually best to apply a couple of lighter applications allowing time in between for the water to soak into the soil. Likewise, on lighter sandy soils that drain more rapidly, infiltration is not so much a problem as is the likelihood of water moving too quickly down through the soil and beyond the grass plant's roots and therefore not benefiting the grass plant. Hence, a split application of water will also be more beneficial for the grass on sandy soils.

While spring has indeed arrived ahead of most years, the tasks of lawn care remain much the same except that they need to be carried out earlier than many of us are used to. Paying attention to prevailing weather conditions and observing what's happening in your lawn are very valuable aids when it comes to understanding what's going on and what to do next.

Be on the Watch for Ticks

Jeffrey Hahn, University of Minnesota Asst. Extension Entomologist

With the early spring we have been experiencing this year, ticks have also been active sooner than normal. The two most common ticks we encounter are the American dog tick (also known as wood tick) and the blacklegged tick (formerly called deer tick). Both of these ticks are found in the underbrush of hardwood forests and adjacent open grassy fields

Both are annoyances because they bite people and our pets as they seek blood meals. However, blacklegged ticks are particularly a pest because of their ability to vector diseases. The most common disease they can transmit in Minnesota is Lyme disease (1,050 cases in 2008). Lyme disease is most common in central and eastern Minnesota. Blacklegged ticks are also known to vector human anaplasmosis (278 cases in 2008), babesiosis (24 cases in 2007), and Powassan virus (2 cases ever reported, both in Cass county).

blacklegged tick close-up.JPG

Photo 1: Blacklegged tick close-up. Jeff Hahn.

There are certain conditions that must occur for a blacklegged tick to successfully transmit a disease to you. First, it must be attached and biting you; if it is just crawling on you, it can not transmit disease to you. Second, if it is attached to you, it must be biting long enough. For Lyme disease, the blacklegged tick must be biting for at least 24 - 48 hours; for human anaplasmosis it needs to be biting for 12 - 24 hours. So if you go out into the woods in the morning and find a blacklegged tick biting you in the afternoon, it is doubtful that it has been attached long enough to transmit Lyme disease or human anaplasmosis.

Up to 30 days after contracting Lyme disease, most people (70 - 80%) experience a red circular rash. They may also experience fever, chills, headache, muscle and joint pain, and fatigue. If left untreated, these symptoms can progress into additional rashes, fever, arthritis, muscle pains, irregular heartbeats, stiff neck, and persistent fatigue. If Lyme disease continues to progress, symptoms that may be experienced weeks or months after the onset of illness can include swelling in joints, like knees, continued persistent fatigue, and nervous system problems.

If you suspect you may have contracted Lyme disease or another tick-borne disease, see your doctor. For information on other tick-borne diseases, go to Tick-borne Diseases in Minnesota.

Prevention is the best method to avoid ticks. Stay on trails when possible. Wear protective clothes, such as long pants and long sleeve shirts (tuck pants into socks for additional protection). Use repellents to maximize your protection. Apply DEET on clothes or skin. Use permethrin just on clothes. Permethrin is effective for several wearings and will be effective even if clothing is washed. It is not necessary to saturate clothing or skin with repellent, just apply enough to covered the desired.
When returning from a known tick area, be sure to check yourself for ticks. Promptly remove any and save for identification. For more information on ticks, see Ticks and Their Control.

Spring Insects Are Early

Jeffrey Hahn, University of Minnesota Asst. Extension Entomologist


Photo 1: Recently hatched forest tent caterpillar.Jeff Hahn.

We are experiencing a noticeably early spring. Consequently this has caused insects to become active earlier than normal. During April, insects such as forest tent caterpillar, European pine sawfly, and pine spittlebug were already active, about 3 - 4 weeks ahead of schedule. Undoubtedly, many garden insects are also active as well. That is not to say all of individuals of a species have become active, but at certain sites they have.

If you are anticipating a particular insect problem for mid May, look now, it probably is already present. If you are looking for an insect that normally comes out in early May, it probably is already is active. Inspect your garden and landscape now for potential insect pests.

Keeping Plants Healthy and Green While Going Green

Michelle Grabowski, University of Minnesota Extension Educator

Regardless of the time and effort put into a garden, inevitably at some point a plant disease will show up. These spots, rots and wilts can be quite distressing to a gardener working to beautify their yard or hoping for a fresh crop of fruits or vegetables. Often the first response to disease problems is to spray a fungicide. Many gardeners however are looking for alternatives to this management strategy. Whether you are going organic, trying to reduce the number of pesticides used in your yard or looking for a simple inexpensive means to reduce plant diseases, cultural control practices can be a great strategy for keeping plants healthy. The US Department of Agriculture Organic rule states that preventive and cultural control practices must be a grower's first choice for pest control. In yards and gardens, preventative and cultural control practices are often effective at reducing disease problems to a level where they are no longer a concern or eliminating them altogether. Combining several of the cultural control practices below can keep gardens healthy without the use of pesticides.

seedlings Y&G.jpg

Photo 1: Healthy basil plants.  M. Grabowski UMN Extension.

Purchase Healthy Plants - Do not accidentally bring plant pathogens into the garden on infected transplants or seed. Carefully inspect all transplants prior to purchase for disease symptoms like leaf spots, discolored areas on stems, leaves or roots. Above ground plant parts should be firm and green. Roots should be firm and light tan to white. Many root hairs should be present. Reject any plants with symptoms of disease. Purchase seed and transplants from a reputable source.

Disease Resistant Plants - Some plants are bred to be resistant to a specific disease. Whenever possible select varieties that have resistance to common diseases. Look for varieties that advertise resistance to specific disease problems like powdery mildew resistant pumpkins or apple scab resistant crab apple trees. General statements like 'good disease resistance' often imply a hardier plant, but these varieties may not include resistance to any specific disease problems.

Scouting and Diagnosis - Examine plants regularly throughout the growing season to find pest problems while they are still minor. Identify the pest causing the problem before taking action. Visit for help in identifying unknown pest problems. Knowing the identity of the pest will allow you to choose management practices effective against that particular pest.

Sanitation - If a plant disease problem is identified on a few leaves, stems or fruit, these plant parts should be promptly removed from the garden. Fungal and bacterial plant pathogens reproduce on infected plant parts. Removing infected plant tissue will reduce the growth and spread of the pathogen within the garden. Remember, never remove more than 1/3rd of a plants leaves. In some cases it is worthwhile to completely remove one severely infected plant to prevent spread of the disease to its healthy neighbors. Infected plant tissue can also be removed from the garden at the end of the growing season to reduce the pathogens ability to survive from one season to the next.

Infected plant parts can be composted if the compost pile heats up to 160F. Otherwise infected plant parts can be buried, burned or disposed of in the trash. Follow local city or county regulations regarding disposal of plant material. Many cities offer municipal composting sites for yard materials.

leaf moist Y&G.jpg

Photo 2: Moisture favors growth of fungal and bacterial pathogens.  M. Grabowski UMN Extension.

Manage Moisture - Most fungal and bacterial plant pathogens thrive in moist environments. Moisture on the surface of leaves and stems allows these pathogens to infect, grow, reproduce and spread. Roots growing in heavy wet soils are prone to root rot. Create an environment that favors plant growth, not disease development, through proper water management.

Use drip irrigation or a soaker hose to water plants. This puts water in the soil, where roots can take it up, not on the leaves, where fungi and bacteria thrive. If using sprinkler irrigation, water early in the morning so leaves dry quickly in the sun. Avoid watering as the sun goes down. Wet leaves will remain wet for many hours in the night, providing excellent growing conditions for fungal and bacterial plant pathogens.
Water deeply and infrequently. This will encourage growth of deep plant roots and will allow soil to dry slightly between watering. Continuously wet soil favors the growth of some root rotting pathogens and can suffocate roots. Amend heavy soils with organic matter to improve soil drainage.
drip irrigation Y&G.jpg

Photo 3: Soaker hose in the flower garden. M. Grabowski UMN Extension.

Mulch the soil with an organic mulch like wood chips or straw. This will keep moisture in the soil and reduce humidity in the plant canopy. Mulch also helps to reduce the spread of plant pathogens that splash from leaf debris in the soil onto the lower leaves of plants.
Space plants to allow good air movement through the garden. This will help leaves dry out quickly after rain and irrigation.

Tolerate a Non-threatening Disease - Remember not all plant diseases are deadly. In fact many common diseases in the yard and garden affect the aesthetics of the plant more than the health of the plant. Learn more about the plant disease you have encountered at before deciding what level of disease control is necessary. Some diseases like oak wilt or Dutch elm disease require action. Others, like powdery mildew on lilac can be tolerated as they will cause no significant damage to the plant.

Dan Miller, Plant Health Specialist, University of Minnesota Landscape Arboretum

JB Image.jpg

Photo: Japanese Beetle. Forestry Images. Russ Ottens, University of Georgia.

The Japanese beetle (Popillia japonica) was first detected in the United States in New Jersey in 1916 and has spread throughout most states east of the Mississippi and to parts of Arkansas, Missouri, Kansas, Oklahoma, Iowa, and Minnesota west of the Mississippi. In Minnesota, the beetles were first detected in 1968. Trapping programs conducted by the Minnesota Department of Agriculture (MDA) showed low but consistent numbers from 1991 to 1998. Trapping data in 1999 and 2000 showed a dramatic increase in Japanese beetles with the highest counts occurring in Washington, Ramsey, Hennepin, Dakota, and Carver counties. After trapping in 2002, the MDA concluded that the beetle was too widespread to be eradicated. The beetle was then deregulated and budget cuts shifted the direction of the program so the statewide trapping program was discontinued.

Arboretum exhibit demonstrates integrated control of Japanese Beetles

In recent years, Japanese beetle infestations have become more noticeable in the metro region with many reported cases of damage to golf courses from the white grub larvae feeding on grass roots and damage to ornamentals shrubs and trees (especially roses, grapes, and lindens) from adult beetles. It is apparent that awareness of the pest is growing; however many home gardeners are not experienced or knowledgeable regarding integrated control strategies for the pest. In 2009, the Minnesota Landscape Arboretum obtained a grant from the North Central Integrated Pest Management Center to create an exhibit at the Arboretum to provide updated, relevant IPM information to the public on environmentally safe ways to control the adults and larvae of the Japanese beetle. The display featured a sign located in the center of a plot of turfgrass and roses with general IPM information, a take-home brochure with more detailed information, and a terrarium so visitors could observe the beetles while they were feeding on plants.

Determining the distribution of Japanese Beetle in Minnesota

A secondary part of the grant involved a survey to determine the current statewide distribution of the beetle. In August 2009, an electronic survey was sent to over 300 golf course superintendents via the Minnesota Golf Course Superintendents Association. In October a second electronic survey was sent to nurseries throughout the state via the Minnesota Nursery and Landscape Association. These surveys provided links for respondents to use in properly identifying the beetle. The survey also asked if beetles or grubs had been observed on their golf course or nursery, when they were first observed, the damage levels, and the control strategies employed. Additionally, over 40 University of Minnesota Extension Educators and Master Gardeners across the state were contacted by phone and asked if they had heard of infestations in their areas. Based on previous trapping surveys by the Minnesota Department of Agriculture and our 2009 consensus surveys, it is apparent that the beetles are primarily located in the seven county metro area and southeast toward Rochester and west toward Mankato (Figure 1). Future IPM control efforts should be focused in these areas.

Even though Japanese beetles have been present in the metro area for several years, they were not observed at the Arboretum until 2007. To get a better understanding of the encroachment of Japanese beetles to the Arboretum, a trapping study was initiated in 2009. Twenty traps were set on golf courses and parks in an approximately 10 mile radius round the Arboretum and compared to traps on the Arboretum grounds. Traps were set in each location once a week, left for 24 hours, retrieved, and beetles were counted. Trapping started on July 17th and continued for ten weeks until September 16th. The most remarkable outcome of this trapping project was the noticeable difference between trap counts on golf courses east of the Arboretum and golf courses west of the Arboretum. The average number of beetles per trap for the four golf courses east of the Arboretum was 483.0 while the average number for the two eastern courses was only 2.6. The average number of beetles for the Arboretum's traps was 5.7. Several golf course superintendents indicated that 2009 was either the first year or the second year that they were aware of the beetle's presence. It appears that the Japanese beetle populations are increasing and are continuing to advance further west. 

Figure 1. Status of the Japanese Beetle in Minnesota in 2009 (PDF available: JapaneseBeetleMN2009V3.pdf)


Methods for decreasing potential damage from Japanese Beetles

Homeowners and golf course superintendents in the metro and southeastern region of Minnesota can decrease potential damage to their ornamentals and turfgrass by scouting and early detection.

Golf courses (and other turf managers) should concentrate their control efforts on the grubs if turf damage is considerable. Imidacloprid and Acelpryn (a reduced-risk insecticide) have proven to be effective.

Homeowners can control small infestations of adult beetles by picking them off the plants and dropping them into soapy water or rubbing alcohol. Pheromone traps are not recommended as beetles may miss the trap and land on nearby landscape plants, causing damage.

If damage is beyond tolerable levels, conventional insecticides may become necessary. Imidacloprid and residual pesticides like pyrethroids are effective for adults but should only be used where infestations are found and not used as preventative treatments.

Homeowner's can treat grub damage using biorational control with products containing halofenozide an insect growth regulator or with beneficial nematodes. It is necessary to confirm that turf damage is caused by white grubs and not by other turf diseases before implementing control methods.

Detection of Japanese Beetles in new counties

If beetles are found in counties not marked on the map in Figure 1, please let us know by sending specimens including capture location and date to Jeff Hahn at Department of Entomology 236 Hodson Hall, 1980 Folwell Ave., St. Paul, MN 55108 or send digital images to

Little Worms Under Elm

Jeffrey Hahn, University of Minnesota Asst. Extension Entomologist

unk. Minnetonka 2.JPG

Photo 1: Elm gall midge larvae on sidewalk. Unknown.

Large numbers of very small, about 1/16th inch long, pinkish worms were found during mid April under elm trees. Looking like grains of rice, these 'worms' are actually a type of fly known as a gall midge. It is not clear what species is present but they appear to attack the developing samuras (winged seeds) in early spring. Later in the spring (sometime in April to early May), the mature larvae drop to the ground where they remain until the next spring. The galls are harmless to the tree and no control is necessary. The larvae can be a nuisance when they fall on driveways or sidewalks. The only necessary step is sweep them off. This is a short lived problem that will go away on their own.

May 2010 Garden Calendar

Contributors: Karen Jeannette, Yard and Garden News Editor
Including Excerpts from the 2010 Minnesota Gardening Calendar

This month Bob Mugaas tells us the crabgrass has emerged early (Home Lawn Care - Recapping the very early spring of 2010 and what's next for timely information about Lawns) and Jeff Hahn says Spring Insects are Early this year, too. Gardeners across the state have been inquiring if they can plant and perform other garden and yard tasks earlier than in past years. Below we provide advice for this gardening season come early.

Advice for the Gardening Season Come Early

When to Plant Flowers

Despite the warmer and earlier growing season, the answer to, "Is it safe to plant perennials and annuals?" is still "Wait until mid-to late May to plant perennials and until after your area is frost free before planting flowering most annuals."

Why Wait?  In most Minnesota locations, perennials can be planted after mid-month, but wait until you're certain there will be no more frost before adding flowering annuals to the garden. Most, including impatiens and geraniums, have no frost tolerance. Pansies, violas, and johnny jump-ups are among the few annuals that will not be killed or badly damaged by frost. Calendulas, snapdragons, and sweet alyssum may also be planted a little early. 

You can identify when your area is likely to be frost-free using the MN spring frost-free map:  

When to Plant Vegetables


Photo 1: Kale and other cool season vegetables can be planted as soon the garden bed is ready. Karen Jeannette.

Which vegetables can I plant and when? You can sow early "cool-season" crops such as lettuce, cabbage, cauliflower, broccoli, Brussels sprouts, and onions immediately after preparing your garden plot.

Warm season vegetables, like tomatoes and peppers should be planted after the last chance of frost.  See "Planting the Vegetable Garden": for guidance on when to plant and how far apart to space your vegetables.

Keep Up with Early Pests and Diseases

Plant Diagnostic Modules: Pictures, simple descriptions, and easy to follow management instructions make it easy to stay ahead or just keep up with plant pests and problems using any of the University of Minnesota Garden Info Diagnostics Modules:

Stay ahead of disease this year with diseases management tips in this month's article by Michelle Grabowski: Keeping Plants Healthy and Green While Going Green

When to Perform Lawn Care

The lawn care calendar guide "Upper Midwest Home Lawn Care for Cool Season Grasses" ( is a helpful guide for scheduling lawn maintenance. However, this month, learn how to adjust your lawn maintenance practices for this earlier than normal growing season with Bob Mugaas' timely article, Lawn Care: Recapping the very early spring of 2010 and what's next for timely information.

For more information on lawn care, see the University of Minnesota Garden Info lawns section:


Are you starting a raised bed? Ordering soil? Adding Compost? Find information on soil topics at the University of Minnesota Garden Info soils section:

You needn't test your garden soil annually, but if plants have grown poorly the past year or two, despite being in a sunny location and receiving normal care, visit U of M Soil Testing Lab web site: .  You'll get a questionnaire with instructions on taking and sending in samples, If the problem is due to a nutrient imbalance, excess alkalinity, or acidity, they'll suggest a remedy, with respect to what you are growing.

Small Fruits

If you'd like to grow some fruit in your yard, but don't have room for apple or pear trees, consider planting Minnesota-hardy blueberries, raspberries, or strawberries. You need an area well-drained soil and plenty of sunlight -- a minimum of six to ten hours daily. More is better. In addition, blueberries need acidic soil to thrive. Have your soil tested for specific information on acidifying your soil before planting them. For more information regarding fruit varieties and culture, see the Fruits section of the U of MN Gardening Information website:


See the Extension listings of garden tours, horticulture diagnostic clinics, workshops, and plant sales @
  • © 2014 Regents of the University of Minnesota. All rights reserved.
  • The University of Minnesota is an equal opportunity educator and employer. Privacy