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May 2012 Archives

Cutworms Gone Wild

Jeffrey Hahn, Asst. Extension Entomologist

Many parts of Minnesota experienced large numbers of adult cutworm moths recently. However, it was not so much the moths that were noticed as were the many eggs that were laid on homes on windows, siding, soffits and other places. Clusters of eggs were reported from the Twin Cities up to northern Minnesota, especially in the northeastern part of the state. Some towns found that essentially all buildings had at least some eggs on them. One resident said he found as many 15 clusters of eggs on his home. Wisconsin also experienced a similar phenomenon with cutworm eggs found in much of the northern half of their state.

Insect eggs are often challenging to identify, especially to species. While it was fairly easy to diagnose the eggs as belonging to a moth, it wasn't until someone was finally able to catch the culprit in the act of laying eggs that the species could be identified as a variegated cutworm. Variegated cutworms are native to Minnesota but it is very unusual to see such large numbers, especially in northern Minnesota where they are rarely seen.

Mike Misk

Photo 1: Variegated cutworm eggs on house

An individual variegated cutworm egg is tiny, about 1/50th in diameter. It is hemispherical with many ridges and is whitish or yellowish at first, before turning brown. There can be hundreds of eggs in a single cluster. Once they hatch, they are small and dark. As they grow larger, they are brownish to black with four to five yellowish diamond-shaped spots on the top of the body starting at the head. You may also see a dark-colored 'W' on top of its body near the posterior. They can be up to two inches long when fully grown.

You might expect that with so many eggs being laid that this would mean an increased problem with cutworms in gardens and agricultural fields. So far this has not been the case. Still, if you noticed clusters of eggs in your area, monitor your garden and watch for signs of cutworms, i.e. young plants cut off at ground level. The eggs laid on homes are little risk to gardens, as the caterpillars are very likely to die before they can move and find susceptible plants.  Click here for more information on cutworms, including management.

May 15, 2012 Issue

Watch Out for These Insects

Jeffrey Hahn, Asst. Extension Entomologist

Insects are out in full force in gardens and yards this spring. Are any of these pests at your home?

Aphids are small pear-shaped, soft-bodied insects. They have been reported on roses and red elderberry this spring so far, but will feed on a wide variety of herbaceous and woody plants.

They feed on plant sap with a long, needle-like mouthparts. Plants typically do not exhibit noticable symptoms when infested by small to moderate numbers of aphids, although large numbers can cause wilting and loss of plant health. There are many natural enemies to help keep aphids under control, especially ladybird beetles. If you are dealing with larger numbers of aphids, try spraying them off with a hard stream of water.
If you need a low impact insecticide, consider insecticidal soap or horticultural oil.

Fourlined plant bugs have just started to hatch.

They feed on a wide variety of herbaceous plants as well as shrubs and fruit. Look for reddish nymphys now (Photo 1);

Jeff Hahn

Photo 1: Fourlined plant bug nymph and damage

eventually they mature into greenish yellow insects with four black stripes. When fourlined plant bugs feed, they produce small, round sunken lesions on the leaves. Large numbers can reduce plant health, although in many cases only smaller numbers are present which cause cosmetic damage.

When practical, crush nymphs that your find; you can also spray them with insecticidal soap. You will need a residual insecticide for the adults.

See also,

There have been several species of sawflies reported recently.

European pine sawfly feeds on the old needles of pine especially mugo pine.

Columbine sawfly feeds on the edge of the leaves of columbine, sometimes feeding until there is nothing left but the midrib.

Roseslug causes a different type of damage on roses. They feed on one layer of leaf tissue, feeding between the veins. At first, this damage looks kind of lacey, as if something sucked the green out of the leaves, Later these damaged areas turn brown.

Sawflies are no more than 1 inch long when fully grown (foseslugs are just 1/2 inch long), so look carefully for them on your plants.

Once your find them, you can use insecticidal soap, horticultural oil, spinosad or a residual insecticide.

Look out for disease problems on new plants

Michelle Grabowski, University of Minnesota Extension

I always recommend that gardeners thoroughly inspect every plant for disease problems before they purchase it. Examine both the upper and lower surfaces of the leaves, especially those leaves closest to the soil. Look at the stems and even the roots. Any spots, streaks, dark discolored or soft, mushy tissue is a warning sign that your new plant may come with a disease problem. Once a new pathogen is introduced into a garden, it may cause problems for years to come. In addition, nursery plants may move across the country before they make it to a local garden center. As a result infected plants can bring new plant diseases to Minnesota.

Boxwood Blight

Virginia Tech, Plant Disease Clinic

Photo 1: Leaf spots and blighting due to boxwood blight

One disease of concern is boxwood blight, a fungal disease caused by Cylindrocladium buxicola (syn C. pseudonaviculatum). Boxwood blight was first identified in the eastern United States in 2011. It has since been found in 8 eastern states as well as in Oregon. To date boxwood blight is known to infect all species of boxwood (Buxus spp.) and Pachysandra sp.

Boxwoods infected with the boxwood blight fungus first develop tan leaf spots with a dark brown border. Chalky white spores form on the lower surface of the leaf just below leaf spots, under humid conditions. Leaf spots grow large enough to blight the entire leaf. Infected leaves fall off, resulting in bare branches throughout the shrub. The fungus also infects branches anywhere from the soil line to the tip of the branch. These infections start out as dark brown to black short lines, and grow to completely encircle and girdle the stem. Roots of the boxwood shrub are not infected by the fungus and remain healthy.

Virginia Tech Plant Disease Clinic

Photo 2: Stem lesions caused by boxwood blight

Boxwood blight has not yet been identified in Minnesota. If you suspect your plant is infected with boxwood blight first use the University of Minnesota Extension's online diagnostic tool for Boxwood to determine if the problem might be a more common look alike. If Boxwood blight appears to be the most likely suspect, please contact the Minnesota Department of Agriculture by sending an email with photos of the plant to or leave a voice message at 1- 888-545-6884. A MDA employee will respond in 1 to 2 days.

Downy Mildew
A second invasive disease to be on the look out for this year is downy mildew of basil. This disease is caused by the fungus-like organism Peronospora belbahrii. Downy mildew on basil was first found in the United States in Florida in 2007. It was seen throughout the eastern states in 2008 and was identified in Wisconsin in 2010. Downy mildew of basil has not been officially identified in Minnesota.

M. McGrath, Cornell University,

Photo 1: Downy mildew symptoms on the upper leaf surface of a sweet basil plant

Only basil plants (Ocimum sp.) are susceptible to this species of downy mildew, although other species of downy mildew can infect other common garden plants. The commonly grown sweet basil, Ocimum basilicum, is highly susceptible and growers have reported 100% crop loss due to the pathogen. Infected plants first display yellowing on the lower leaves. As the disease progresses these leaves develop dark brown to black spots. If the lower surface of infected leaves is examined, gardeners will notice that the leaves look dirty, or are covered with a thin layer of gray to brown fungal growth. This dirty looking fungal growth includes spores and spore producing structures of the downy mildew pathogen.

The downy mildew pathogen can move into a garden on infected seed, transplants or on wind currents. Unlike other downy mildew pathogens that prefer cool weather, basil downy mildew will tolerate cool weather but thrives in warm conditions. This means that the pathogen is actively growing and spreading for most of Minnesota's growing season.

At the end of April, University of Wisconsin plant pathologist Amanda Gevens reported identification of basil transplants infected with downy mildew, available for sale at a local store in Wisconsin. This early arrival of the pathogen in the Midwest could mean that more severe disease is found in the region this year as the pathogen will have time to grow and spread.

S. Jensen, Cornell University,

Photo 2: Dark growth on the lower leaf surface of a plant infected with basil downy mildew

Avoid downy mildew of basil by purchasing only healthy transplants and spacing plants to provide good air movement and quick drying of leaves after rain or dew. The basil varieties 'Spice' 'Blue Spice' and 'Blue Spice Fil' have been reported to have good resistance to downy mildew. 'Genovese', 'Martina', 'Italian Large Leaf' and 'Superbo' are all highly susceptible to the disease. 'Red Leaf' 'Red Rubin' 'Lemon' 'Lemon Mrs. Burns' 'Lime' and 'Sweet Dani Lemon Basil' were susceptible to downy mildew but had fewer symptoms than the most susceptible varieties.

If you suspect your basil plants are infected with downy mildew, please contact the Minnesota Department of Agriculture by sending an email with photos of the plant to or leave a voice message at 1- 888-545-6884. A MDA employee will respond in 1 to 2 days.

Karl Foord - Extension Educator, Horticulture

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

Great White Trillium, Trillium grandiflorum

Karl Foord

Photo 1: Great White Trillium (Trillium grandiflorum)

False Solomon's Seal (Maianthemum racemosum, syn. Smilacina racemosa)

Karl Foord

Photo 2: False Solomon's Seal (Maianthemum racemosum)

Lungwort, (Pulmonaria officinalis)

Karl Foord

Photo 3: Lungwort (Pulmonaria officinalis

Heucherella 'Stoplight' (Hybrid of Heuchera and Tiarella)

Karl Foord

Photo 4: Heucherella 'Stoplight'

Foam Flower, Tiarella 'Sugar and Spice' and Lungwort, Pulmonaria 'Trevi Fountain'

Karl Foord

Photo 5: Foam Flower (Tiarella 'Sugar and Spice')

Jacob's Ladder, Polemonium reptans 'Stairway to Heaven'

Karl Foord

Photo 6: Jacob's Ladder (Polemonium reptans 'Stairway to Heaven')

Lenten Rose, Helleborus orientalis

May 1, 2012 Issue

Native Grasses for Wildlife

Mary Meyer, Extension Horticulturist and Professor

Grasses, especially native grasses, can attract a wide range of wildlife and insects. While you might first think of the cover grasses provide in summer and winter, they also supply food for many grassland birds and are critical for butterfly larva food. Planting a prairie gives you the best environment for wildlife habitat; however, you can still make an impact with grouping 2-4 kinds of grass and using 3-5 plants of each kind. You could even try a stylized prairie by grouping the grasses in drifts similar to a traditional border. Diversity in a garden not only looks good, but can attract a wider variety of insects and birds. Leaving the grasses standing in winter can provide cover and winter shelter to wildlife. We rarely think of grasses being attractive, let alone critical for butterflies, but many species of skippers, satyrs, pearly eyes, wood nymphs, and browns, REQUIRE grasses and sedges as larval food, so these plants attract a number of butterflies as sites to lay their eggs.

Mary Meyer

Photo 1: A skipper butterfly rests on feather reedgrass. Skippers are a large group of butterflies whose larvae feed on grasses.

Grasslands, which not surprisingly, are predominately grasses, have lost 1,000s of acres to development and agriculture, resulting in drastic declines in grassland birds. Of the 37 species of grassland birds that appear to be reasonably well monitored by the North American Breeding Bird Survey, 32 are demonstrating some form of decline, while only 5 are experiencing some form of increase (Sauer, 2005). Habitat loss is the main reason cited for decline in these grassland species. Adding native grasses in your garden can increase the diversity of your garden and provide a home for native butterflies and birds.

Inviting wildlife into your garden is great especially if it's birds, butterflies, honey bees and other pollinators. What about mice, ticks, snakes and mosquitoes? Yes, this 'less desirable' wildlife lives in grasslands and is all part of nature! Making sure your home is properly sealed from openings for wildlife, wearing protective clothing when walking in tall grass, eliminating standing water for breeding mosquitoes, and mowing paths through areas you want to keep natural are precautions and means for living with the less favorite forms of wildlife.

Click the link below to see table 1 which lists common native grasses and the range of wildlife these plants can attract.

Grasses for Wildlif1.pdf

Species Fact Sheets:
BirdLife International. 2004. Grassland birds are declining in North America. Presented as part of the BirdLife State of the world's birds website. Available from:
Sauer, J. R., J. E. Hines & J. Fallon, 2005. The North American Breeding Bird Survey, Results and Analysis 1966 - 2004. Version 2005.2. USGS Patuxent Wildlife Research Centre, Laurel, MD

Michelle Grabowski, UMN Extension

JAR Y&G.jpg

N. Gregory, UDEL,

Photo 1: Sporulating gall of Japanese apple rust on juniper

Cool wet spring weather stimulates galls of several rust fungi (Gymnosporangium spp.) to produce bright orange gelatinous spore producing structures that readily catch a gardeners eye. Several species of Gymnosporangium rust fungi are native to Minnesota and infect eastern red cedar trees, Juniperus virginiana during part of their lifecycle and trees and shrubs from the Rosaceae family during a different part of their lifecycle. Native Gymnosporangium rusts include cedar apple rust, quince rust, hawthorn rust and juniper broom rust. Photos and descriptions of these plant diseases can be seen at the UMN Extension online plant diagnostic tool What's wrong with my plant?

A new Gymnosporangium rust has recently been found in the United States but not yet in Minnesota. Japanese apple rust is caused by Gymnosporangium yamadae. This fungus does not infect Minnesota's native red cedar trees but does infect Juniperus chinensis and J. squamata. Both of these species of juniper are sold as ornamental trees or shrubs here in Minnesota. Although Japanese apple rust is unlikely to cause any serious damage to junipers, this fungus also infects apple trees. At this time, it is unknown how the apple varieties grown in Minnesota will respond to Japanese apple rust.

To identify Japanese apple rust in juniper, look for round woody galls that are 1/2 to 1 inch in diameter. When wet, these galls become covered in a 1/4 inch thick layer of orange gelatinous goo. As this spore filled goo dries, it will become apparent that they arise from short orange projections, like small shelves sticking out from the side of the gall. In contrast, the native cedar apple rust galls produce orange gelatinous tentacles that swell to 1-2 inches long when wet.

If you suspect a juniper in your area has Japanese apple rust, please contact the Minnesota Department of Agriculture by sending an email to or leave a voice message at 888-545-6884. The MDA will contact you with further information in 1-2 days.

Forest Tent Caterpillars Are Out Now

Jeffrey Hahn, Asst. Extension Entomologist

Did you have a problem with forest tent caterpillars (FTC) last year? If you did, expect to see them again soon as they have started to hatch during late April. You can recognize these caterpillars from their blue and black body and white footprint or keyhole shaped spots on their back. Despite their name, FTC do not construct conspicuous webs. If you find a large tent in a tree this spring, that is from eastern tent caterpillars.

Jeffrey Hahn

Photo 1: Forest tent caterpillar and damage

FTC are primarily a problem because they feed on the leaves of trees and shrubs, especially aspen, birch, oak, and linden/basswood. If they are abundant and their normal food is in short supply they will crawl down trees and also feed on fruits, vegetables, and flowers. They can also become nuisances when they wander around looking for sites to pupate (which has earned them the nickname 'armyworms'). This can lead them to crawl onto nearby buildings and other structures.

Populations of FTC are cyclical, with periods of few and increasing numbers of FTC lasting about 8 - 13 years. Eventually these increasing numbers hit outbreak numbers which lasts about three to four years. FTC populations in the Twin Cities, though, appear to be less cyclical.

Fortunately, healthy, mature trees can tolerate severe defoliation, even in several consecutive years. Young and unhealthy trees are more susceptible to injury and should be monitored closely for the potential need to treat. There are a variety of residual insecticides that you can use if you want to protect your plants. Consider using products that have a low impact on the environment, such as Bacillus thuringiensis, spinosad, and insecticidal soap. Bacillus thuringiensis is a particularly good product if the tree is flowering since it will not harm visiting honey bees.

There are also insecticides available to protect garden plants, including food crops. Be sure to check the label to be sure the particular product you want to use is cleared to treat the plants you wish to protect.

An Imprelis Update

Kathy Zuzek, UMN Extension Educator, Horticulture

The History of Imprelis
In October of 2010, a new broadleaf weed killer by the name of Imprelis became available to turf professionals. Key to DuPont's release of this herbicide was its effectiveness at very low concentrations, its low toxicity to humans and other mammals, and its effectiveness on difficult-to-control turf weeds such as creeping Charlie, wild violets, clover and Canada thistle.

During the spring of 2011, damage to ornamental plants in landscapes where Imprelis had been applied began to appear in the eastern half of the United States including Minnesota. Damage to new growth of plants became visible within a matter of weeks after an Imprelis application and included twisting and/or browning of shoot tips, leaves, and needles (Photo 1).

K. Zuzek

Photo 1: Brown, twisted, & drooping shoot tips from Imprelis applications

As the summer progressed, impacted shoots and their associated leaves, needles, and buds often died on the most susceptible species. In some cases, entire trees or shrubs died. Broadleaf and conifer species of ornamental plants were impacted but conifer species were impacted much more severely. The most seriously impacted species from states east of Minnesota were Norway spruce (Picea abies) and eastern white pine (Pinus strobus) trees. The most seriously impacted species in Minnesota were white spruce (Picea glauca) and eastern white pine, but noticeable damage to Colorado blue spruce (Picea pungens), Norway spruce, Austrian pine (Pinus nigra), red pine (Pinus resinosa), and arborvitae (Thjuja occidentalis) were also common. A wide range of damage was seen among all of these species. Some plants showed little injury throughout the 2011 growing season, others died quickly, and the symptoms on others became more severe as the growing season progressed. The number of plants damaged, the level of damage, and plant mortality was highest among white spruce and eastern white pine in Minnesota.

In August of 2011, sales of Imprelis were stopped but damage to trees and shrubs in landscapes continues to be an issue. DuPont initiated a claims resolution process to compensate customers with damaged or killed plants. The deadline for claims submission was February 1, 2012 and DuPont is now processing claims submissions. Lawsuits have also been filed against DuPont.

How Imprelis Works
Aminocyclopyrachlor is the active ingredient in Imprelis and is classified as a synthetic auxin or growth regulator type of herbicide. Imprelis and other growth regulator herbicides are absorbed by roots and leaves and then move via the xylem & phloem to two of the meristematic regions responsible for new plant growth: shoot tips and root tips. In susceptible plants, growth regulator herbicides produce characteristic twisting and curling of the shoot tips and their foliage and plant mortality often follows. Herbicides are meant to kill and eliminate targeted plants such as weeds. When they impact non-targeted plants such as conifers in the case of Imprelis, problems arise.

Imprelis does not bind well to soil particles and is a very water-soluble compound. It is also a very stable compound in soil. Because it is active over a long period of time in soils and because its low adsorption and high solubility allow it to move downward in soil once applied to turf, it appears that Imprelis was able to reach the root systems of ornamental plants. Absorption of the herbicide occurred through the roots of these plants, followed by movement through the plant to new growth areas, and injury occurred. It is still not known why particular spruce and pine species are so susceptible to Imprelis.

K. Zuzek

Photo 2: Branch with active bud-break


K. Zuzek

Photo 5: Branch with no bud-break

Will Trees Damaged by Imprelis Recover? The answer to this question depends on the severity of damage. Trees that showed minimal damage (such as a small amount of injury at shoot tips in the upper branches of a tree) during the spring of 2011 and had little additional decline during the growing season will probably survive.These trees have active bud-break and are putting on new growth throughout most of their crowns this spring (Photo 2). Most broadleaf trees and shrubs and some of the conifer species that were impacted by Imprelis are in this group. Retaining these trees and shrubs in the landscape will depend on how badly damage impacts their appearance. Care of these plants during the recovery period should include irrigating the plants during dry periods to minimize moisture stress, avoiding over-watering that can cause additional stress, and avoiding fertilization for a minimum of one growing season to avoid excess growth that can compound herbicide injury.

Trees that showed damage last spring (Photo 3), further decline (dieback of shoots, dead needles and buds, yellowing of the tree canopy) during the 2011 growing season and/or the winter of 2011-2012 (Photo 4), and limited or no bud-break throughout the tree crown this spring (Photo 5) will probably continue to decline and then die. Even if these trees do not die, they will be of little or no aesthetic value in the landscape. In Minnesota, the majority of trees in this group are white spruce and eastern white pine.

K. Zuzek

Photo 3: Initial symptoms on white spruce in July, 2011

K. Zuzek

Photo 4: Symptoms on the same white spruce in April, 2012

DuPont's Compensation Plan If you are a property owner with Imprelis-damaged plant materials and you and your lawn care professional are part of the claims resolution process that DuPont enacted, you can access information on the claims process here. Compensation will cover removal and disposal of impacted trees, replacement costs or direct payment for removed trees, care of replacement trees , two-year warranties for all replacement trees and for any other trees impacted by Imprelis over the next two years, maintenance of impacted trees as they recover, and additional compensation for inconveniences associated with Imprelis.

Removal and Disposal of Plant Materials and Soil containing Imprelis
Listed below are some of Dupont's recommendations for the disposal of plant materials and soils containing Imprelis. These recommendations are for individuals who had Imprellis damage to plant materials but are not part of the claims process against DuPont. You can access the full list of recommendations here .

    Disposal Recommendations
  • No tree debris should be left on site.
  • DuPont recommends disposal of tree and excavated soil materials in solid waste landfills that will accept such waste.
  • The Imprelis label prohibits the use of grass clippings for mulch or compost.
  • Under no circumstances should tree material be used for mulch or compost or disposed of in facilities that would turn it into compost or mulch (e.g., recycling).
  • Trees that are cut down may be used for lumber, firewood, or to fuel various wood burning processes if such usage is otherwise consistent with state, regional and local regulations. Open burning is also an alternative if approved under local regulations.
  • If not landfilled, excavated soil should be disposed of in locations where it will not impact any other plantings through direct application or runoff. With the property owner's consent, excavated soil may be used on site as long as it is applied well away from desirable plant root.
Recommendation for planting replacement plants:
  • To address potential effects of Imprelis remaining in the soil, activated charcoal (that serves to deactivate any residual herbicide) should be applied to the backfill soil in accordance with manufacturer's instructions:

  • For liquid applications, apply at a rate of 1 pound of activated charcoal in each gallon of water uniformly to sides and bottom of hole dug for tree planting as well as to the complete root ball of the tree to be planted. Also, spray the burlap covered root ball if burlap is left in place. Thoroughly coat to the point of run-off the surfaces of the hole and the root ball.

    For dry applications, during tree planting, apply activated charcoal at a rate of 7 to 14 lbs/1000 cubic feet of soil and thoroughly mix with the clean soil. Use this soil as the new backfill soil when planting the tree.

  • Excavated soil should not be used as backfill. New soil, of a similar nature as the existing soil, should be used to backfill around the root ball. No fertilizer should be added to the backfilling mixture.

  • The replacement plant should be watered according to nursery recommendations.

  • The property owner should ensure adherence to best management practices consistent with the geographic area in which it is performing this work, taking into account any unique environmental and climate conditions, and any state, regional or local ordinances. Information on selecting, planting, and care of trees in Minnesota can be found here.

Based on the degradation rate of Imprelis in soils and on recommended planting times for Minnesota, a good additional recommendation would be to not plant susceptible species into Imprelis-impacted landscapes until September of 2012.

Karl Foord - Extension Educator, Horticulture

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

Trout Lily (Erythronium americanum)

Karl Foord

Photo 1: Trout Lily (Erythronium americanum)

Virginia Bluebells (Mertensia virginica)

Karl Foord

Photo 2: Virginia Bluebells (Mertensia virginica) flower

False Rue Anemone (Enemion biternatum)

Karl Foord

Photo 3: False Rue Anemone (Enemion biternatum)

Minnesota Dwarf Trout Lily (Erythronium propullans)

Clover Mites in Homes

Jeffrey Hahn, Asst. Extension Entomologist

Some people have been experiencing clover mites around their homes recently. Identification is important as they could be misidentified as other types of mites or even very small ticks. Clover mites are about the size of a pinhead (about 1/30th inch long) and are reddish or brownish in color. They have a round body and eight legs with the first pair of legs particularly long. People find them on the outside of their homes as well as around windows.

Rayanne Lehman, PA Dept of Agriculture,

Photo 1: Clover mite

Clover mites feed on grass and clover during summer (they are not pests on these plants). They take shelter in and around buildings during the fall. You might see them then but they are much more commonly noticed during spring. They can potentially occur in very large numbers around buildings and have no problem getting inside, especially around windows, because of their small size. They love being in the sun and are most common on the south sides of homes. Fortunately, clover mites are not harmful to people or our property. However, they can stain surfaces if they are crushed.

If you are not seeing many, the best bet is physical removal. Use a vacuum cleaner or gently wipe them up with a damp cloth to help minimize crushing them. Clover mites are a temporary problem that will go away on its own when the weather become warmer.

If you having a problem with large numbers entering your home, you can treat the foundation to deter them with an insecticide containing bifenthrin (be sure it is labeled for spraying the outside of homes). You can also consider hiring a professional pest control service to treat your home's exterior.

If you deal with this problem most years and are looking for a more sustainable approach to managing them, you can try maintaining a barrier of clean, bare soil around your home, i.e. free of grass and leaves. Clover mites generally do not cross such a barrier. This barrier should be about 18 - 24 inches wide. If you do have annuals, perennials, or shrubs planted in this zone, have them far enough apart so the clover mites can not easily bridge across this barrier. Landscape rock apparently is not enough of a deterrent to keep clover mites away from buildings.

Downy Mildew on Impatiens

Michelle Grabowski, UMN Extension

M. Grabowski, UMN Extension

Photo 1: Symptoms of Impatiens Downy Mildew

If you grew impatiens last summer, you may have noticed that some plants were stunted, turned yellow, and soon became barren stalks with perhaps one or two small yellow leaves clinging to them. These symptoms are caused by downy mildew, a disease caused by the water mold Plasmopara obducens. Had you turned a leaf over, you would have seen a fluffy white fungal 'down' covering the lower surface of the leaf.

Downy mildew of impatiens has been observed in the United States since 2004, but became widespread and highly destructive in 2011. Cool wet weather likely contributed to the disease epidemic of 2011 since the downy mildew pathogen thrives under these conditions.

Plasmopara obducens produces tough survival spores called oospores that can overwinter in soil and plant debris. As a result if downy mildew was present in your garden last year, it is likely to show up again in 2012. Downy mildew can also move in on wind blown spores. Although it is not known how far the downy mildew pathogen can travel by wind, a close relative, downy mildew of cucurbits, has been shown to move over 600 miles in 48 hrs. Plasmopara obducens does not move on seed, but it could move into a garden on infected transplants. Inspect all new impatiens for yellowing of leaves, stunting and white fluffy growth on the lower leaf surface. Nurseries producing impatiens are well aware of the threat of downy mildew and are scouting regularly to find and control the pathogen.

M. Grabowski, UMN Extension

Photo 2: Downy like growth on the lower surface of an infected impatiens leaf

Once the impatiens are in the ground for 2012, inspect the plants weekly for symptoms of downy mildew. Yellowing and stunting of the plants are typically the first symptoms observed. Downy white growth on the lower leaf surface confirms the disease. If downy mildew shows up, promptly bag and remove infected plants to reduce spread to neighboring plants. Space plants to allow air movement between plants. This will help reduce humidity and leaf moisture. If beds were infected in 2011, consider choosing a different annual plant this year. Downy mildew of impatiens only infects Impatiens walleriana, the standard impatiens. New Guinea impatiens, impatiens hawkerii are highly tolerant of the disease. No other plants are infected by this pathogen, so Begonias, Caladiums and other shade tolerant ornamentals are good choices as well.

Karl Foord - Extension Educator, Horticulture

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

American Pasqueflower (Anemone patens) and Prairie Smoke (Geum triflorum)

Karl Foord

Photo 1: American Pasqueflower (Anemone patens)

Karl Foord

Photo 2: Prairie Smoke (Geum triflorum)

Bloodroot (Sanguinaria canadensis)

Karl Foord

Photo 3: Bloodroot (Sanguinaria canadensis

Double Bloodroot (Sanguinaria canadensis 'Multiplex')

Karl Foord

Photo 4: Double Bloodroot (Sanguinaria canadensis 'Multiplex'

Marsh Marigold (Caltha palustris)

Karl Foord

Photo 5: Marsh Marigold (Caltha palustris)

Wild Ginger (Asarum canadense)

Karl Foord

Photo 6: Wild Ginger (Asarum canadense)

Karl Foord - Extension Educator, Horticulture

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

Pigsqueak (Bergenia cordifolia)

Karl Foord

Photo 1: Pigsqueak (Bergenia cordifolia)

Lenten Rose (Helleborus orientalis 'Ivory Prince')

Karl Foord

Photo 2: Lenten Rose (Helleborus orientalis 'Ivory Prince')

Bleeding Heart (Dicentra spectabilis 'Gold Heart')

Karl Foord

Photo 3: Bleeding Heart (Dicentra spectabilis 'Gold Heart')

Plant Video Library - Bulbs I

Karl Foord - Extension Educator, Horticulture

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

Glory of the Snow (Chionodoxa luciliae)

Karl Foord

Photo 1: Glory of the Snow ( Chionodoxa luciliae) flower close-up

Checkered Lily (Fritillaria meleagris)

Karl Foord

Photo 2: Checkered Lily (Fritillaria meleagris) flower

Species Tulips (Tulipa tarda)

Karl Foord

Photo 3: Species Tulips (Tulipa tarda)

Garden Hyacinth (Hyacinthus orientalis)

Karl Foord

Photo 4: Garden Hyacinth (Hyacinthus orientalis)

Autumn Lily (Lycoris squamigera)

Karl Foord - Extension Educator, Horticulture

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

Triumph Tulip (Tulipa 'Gavota)

Karl Foord

Photo 1: Triumph Tulip (Tulipa 'Gavota')

Grape Hyacinth (Muscari armeniacum)

Karl Foord

Photo 2: Grape Hyacinth (Muscari armeniacum)

Daffodils (Narcissus)

Karl Foord

Photo 3: Daffodils (Narcissus"Saint Keverne')

Dwarf Bearded Iris (Iris 'Joyce McBride)

Karl Foord - Extension Educator, Horticulture

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

Barrenwort (Epimedium x rubrum)

Periwinkle (Vinca minor 'Dart's Blue')

Pennsylvania Sedge (Carex pensylvanica)

Karl Foord - Extension Educator, Horticulture

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

Sungold and Moongold Apricots (Prunus armeniaca mandshurica 'Sungold' & 'Moongold'

Karl Foord

Photo 1: Apricot Flower (Prunus armeniaca)

Karl Foord

Photo 2: Young Apricot Fruit (Prunus armeniaca)

Regent Serviceberry (Amelanchier alnifolia 'Regent'

Karl Foord

Photo 3: Regent Serviceberry (Amelanchier alnifolia 'Regent'

Northern Strain Redbud (Cersis canadensis 'Northern Strain')


Karl Foord

Photo 4: Northern Strain Redbud (Cersis canadensis 'Northern Strain')

Emerald Triumph Viburnum (Viburnum 'Emerald Triumph')

Karl Foord - Extension Educator, Horticulture

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

Acrocona Norway Spruce (Picea abies 'Acrocona')

Karl Foord

Photo 1: Acrocona Norway Spruce (Picea abies 'Acrocona')

Clove Currant (Ribes odoratum)

Karl Foord

Photo 2: Clove Currant (Ribes odoratum) flower

Flowering Crabapple (Malus hybrida 'Indian Summer')

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