Yard & Garden Line News Volume 3 Number 12                                                               August 1, 2001

Features this issue: Plants to Avoid, Around Your Home or Lake Place Cracks and Splits in Tree Trunks Sclerotinia Blight Sclerotium rolfsii-The Other White Mold MPR Goes to the Arb Growing Herbs? Try Herb Butter Grand Rapids Hosts Hort Night Those Little Black ‘Bugs' in Homes Stable Flies What Are Those Red Bugs in Your Garden? Dobsonflies Editorial Notes

Plants to Avoid, Around Your Home or Lake Place
Deborah Brown, Extension Horticulturist

Poison ivy. Photo credit: Beth Jarvis

Without a doubt, poison ivy, more than any other plant, can wreak havoc with our enjoyment of Minnesota's woodlands and natural wilderness areas. As builders expand development at the fringes of our towns and cities and around some of our more popular lakes, poison ivy can also show up in people's yards. And despite the age-old warning, "leaves of three, let it be," people often discover its presence the hard way!

Part of the problem is that people really don't expect to run into poison ivy at home. And not all plants with three leaves or leaflets joined together are toxic.

Hog peanut, for instance, is a nuisance weed that grows exceedingly well in partial shade, twining around other plants in the area. It has the same leaf configuration as poison ivy, but the leaflets have less substance to them; they're lighter green, thinner, and usually smaller. And you can pull them to your heart's content without developing a rash.

The poison ivy that grows in northern latitudes doesn't vine and climb trees and telephone poles as it does a little bit south of us. Instead, it is a dwarf shrubby plant or ground cover that comes back from perennial roots each spring. Leaves are always grouped in sets of three leaflets with each mature leaflet two to four inches in length and pointed at the tip. Petioles or leaf stems supporting each set of three leaflets are arranged alternately rather than in pairs across from each other. These plants spread by underground creeping roots so you may see a string of them popping up, each a few feet from the other.

Vining poison ivy, near Wash. DC Photo credit: Beth Jarvis

Sometimes people worry about contacting poison oak or poison sumac, both nasty plants in their own right. But poison oak is not thought to grow as far north as Minnesota. Poison ivy leaves are quite variable in their shape, however. Some are lobed, so could easily be mistaken for poison oak, which resembles oak leaves. Not that it makes much difference; the results of tangling with poison ivy OR poison oak are pretty much the same.

(True poison oak may be distinguished by looking at the undersides of its leaves. They're lighter colored than the surface, and covered with fine, velvety hairs. Poison ivy does not have hairy foliage.... not that you'd want to check it out.)

Poison sumac can be found in Minnesota, but luckily, it lives in places that are wet and generally inaccessible, such as swamps, bogs, and moist ditches. Rest assured, the sumac that covers so many Minnesota hillsides, turning brilliant crimson each autumn, is not toxic in any way. In over twenty years of looking at samples people have sent to the University, I've only seen poison sumac once, from a hapless couple who had dug it in the wild and lined both sides of their rural driveway with it. Ouch!

Control

Of course, the important question once you've detected poison ivy on your property, is how to get rid of it. If plants are fairly small, you can dig them out. Just be careful how you dispose of them. Have them hauled away in the trash or dig a hole and bury them. Keep them out of your compost pile.

You can also use herbicides to eliminate poison ivy, regardless of plant size. A woody brush-killer containing the active ingredient triclopyr (sold under brand names such as Brush-B-Gone, and others) may be sprayed or painted on individual plants. Wait until their leaves have expanded fully in late spring, but stop once it begins to show fall color. Glyphosate (RoundUp), another alternative, has also proven successful but may require more applications to get the job done.

Target individual plants. Indiscriminate use of these herbicides will result in killing adjacent plants. To apply them, choose a day when temperatures will not exceed 85 degrees, there's little or no wind, and your don't expect rain for at least twenty-four hours.

Stinging Nettle

Wood nettles. Photo credit: Beth Jarvis

Though nowhere as dangerous as poison ivy, stinging nettles are also perennial plants that should be avoided and eliminated in home gardens and landscapes where people might get into them. These plants don't cause the miserable rashes and weeping blisters associated with poison ivy, but they do sting or smart when you touch them. This burning sensation usually subsides in a matter of minutes but until then, it's decidedly painful and unpleasant.

Look for upright plants with single leaves arranged in pairs opposite each other on the stem. They're light green, not at all woody, and the leaves are coarsely toothed or jagged along the edges. All parts of the leaves are covered with long hairs like little hypodermic needles. When you touch the hairs their tips break off leaving sharp points that scratch your skin and deliver their irritating contents.

Stinging nettles are often found growing in clumps, since once they're established they develop underground runners that send up additional plants. Obviously, it's best to get rid of them while they're still fairly small, before they start multiplying this way. Dig them out or spot spray them, individually, with glyphosate or any broad-leaf weed-killer.

Wood nettles, a close relative, usually aren't a problem in home landscapes as they thrive in dense shade. They're primarily found growing in woodlands or in moist soil near streams or lakes. Leaves tend to be more heart-shaped than those of stinging nettles, and they're arranged alternately on the stem rather than in pairs. Otherwise, they pose virtually the same threat to anyone who touches them.

To send a suspicious plant to the Yard & Garden Clinic for identification wrap it in dry paper towels and mark clearly on the envelope that it may be poison ivy (stinging nettles don't pose much threat once they're limp), so we don't find out the hard way. Please enclose a check for $5 made out to the University of Minnesota. Mail the sample to Yard & Garden Clinic, 1970 Folwell Avenue, St. Paul, MN 55108, early in the week so it doesn't sit around the post office over the weekend.

Cracks and Splits in Tree Trunks
Patrick Weicherding, Extension Educator - Horticulture, Anoka County

Frost crack on maple. Photo credit: Patrick Weicherding

Cracks and splits in tree trunks are fairly common and may occur for various reasons. They are usually not a significant threat to the tree but may provide entry points for insects and diseases. Typically there's not much you can do about them once they occur.

One of the most common types of trunk injury we see in Minnesota is known as "frost cracking." Frost cracks are longitudinal cracks that occur in the bark and wood often extending several feet up and down and penetrating several inches into the trunks of affected trees. They are most evident in winter at temperatures below 15° F. when the wound opens, producing a long, deep slit in the trunk. Frost cracks often close and callus over during the summer, only to open again in subsequent winters. This callusing and recracking may lead to the formation of large "frost ribs" on the side of affected trees.

Frost cracks occur when it gets very cold, very fast, late at night. We hear them crack (it sounds like a loud rifle shot) and we see the results. For years we concluded that when a tree trunk warmed by the sun chills rapidly the outside layers cool and shrink faster than the inside creating physical stresses that result in the tree cracking open. Sounds logical, but if cold temperature is the sole source of these problems, then all trees would have frost cracks. Since most trees do not crack there must be some other explanation.

We know there are species of trees that are more susceptible to frost cracking (oak, maple, linden and willow) but to date no one can fully explain why some tree species and not others, or some individuals within a species and not others, are especially susceptible to frost cracks. We also know that isolated trees and trees growing on poorly drained soils are particularly prone to frost cracks. And, we've speculated that frost cracks may be associated with internal defects resulting from previous injury to the trunk years prior to splitting. (The theory is that defective wood does not contract as readily as the outer layers of healthy wood when winter temperatures plunge rapidly. The strain between the outer, contracting layers of wood and the inner defect causes the outer layers of wood to crack.).

These are all fine observations but has there been any definitive research done to help us solve this mystery? Fortunately the answer may be yes.

Dr. Robert Miller, Professor of Urban Forestry at the University of Wisconsin-Stevens Point, may have the answer. For more than a decade Dr. Miller has been teaching a course titled "Tree Structure and Function" where students learn about trees by dissecting them. Dr. Miller and his students have dissected hundreds of trees with frost cracks, and they are always able to follow the crack into an internal defect where the problem originated. The defects they observed were many, but generally fell into three categories: trunk injuries, broken or torn branches and flush pruning wounds, all of which had been covered over with new wood.

Here's Dr. Miller's explanation: "As these kinds of injuries close over with woundwood, the callus tissue making the woundwood fuses together and seals over the injury. However, areas of structural weakness typically form where the woundwood joins together over the injury, and at the edges of the original wound, especially if the woundwood rolls over the edge of the wound. Years may pass until all evidence of the injury is buried under new wood. But as the tree warms by day and cools by night, physical stresses start the process of splitting the wood from weak areas at the original injury towards the surface. Slowly the crack works its way to the surface until finally on a cold night the tree splits open."

What can be done to prevent frost cracks? They can be prevented by avoiding trunk injuries and by proper pruning. In other words, avoid wounding trees when they are young. Be particularly careful not to injure the stem with mowers or string trimmers. Mulch around young trees and be sure to give them plenty of water.

Sclerotinia Blight
Janna Beckerman, Extension Plant Pathologist

Sclerotia found in plant stems. Photo credits: Plant Disease Clinic

Apothecium. Photo credit: Plant Disease  Clinic

White mold is a serious problem not only in the soybean fields, but in the gardens and flower beds of Minnesota. The disease is caused by the fungus, Sclerotinia sclerotiorum, and it attacks over 170 species of plants! The broad host range that occurs with Sclerotinia blight is rather unusual. Especially susceptible plants include bean, crucifers, carrot, cucumber, eggplant, white (Irish) potato, lettuce, pepper and squash.

Symptoms of this disease begin with a dark and discolored, watery rot. In early stages of development, foliage may show little sign of attack (e.g., One caller reported that his peony was not flowering). Foliage above the lesion wilts and begins to die. Succulent stems may collapse as the base and stem are infected (Note: A key symptom of our nonflowering peony). High humidity and free moisture encourages the development of mycelium (threads of white, cottony fungal growth) . The fungus can rapidly engulf and girdle the stem of the infected tissue, or completely cover infected fruit. Eventually, this white mycelial growth develops into yellow and eventually black overwintering structures (called sclerotia or sclerotes), which resemble rodent droppings, and usually occur in the stem of the plant. The sclerotia serve as overwintering structures. It should be noted that in dry weather, a canker can form without a watery rot.

In the spring, under cool conditions, sclerotia germinate and produce an apothecium, a cup shaped structure on a stalk emerging from the sclerotium. Water droplets land in the "cup," and splash, allowing for spore spread. Sclerotia can also germinate and directly infect nearby plants.

Control options for Sclerotinia blight are limited. Discard infected plants and surrounding soil. Do not compost them! Try to avoid planting susceptible plants for several years. Immune hosts include sweet corn and onions. Currently, Mancozeb, is labeled for control of white mold.

Sclerotium rolfsii-The other white mold
Janna Beckerman, Extension Plant Pathologist

Mature sclerotia on astilbe. Photo credit: Janna Beckerman

Like plants, fungi have specific host ranges. One does not expect to see dogwood anthracnose in Minnesota, even though we do have members of the Cornus genus naturally occurring here. This would lead us to conclude that our environmental conditions (i.e., winter) somehow prevents the fungus that causes dogwood anthracnose from gaining a foothold here. There are numerous diseases that occur "down south" that we don't anticipate ever seeing in Minnesota. We call these fungal pathogens "tropical" or "subtropical." Finding one of these pathogens is akin to a Minnesota birdwatcher finding a penguin at their birdfeeder.

In mid- July we were contacted by a Master Gardener who thought she had Sclerotium rolfsii, also known as southern blight, in Ramsey, Minnesota. We were skeptical. Originally, we figured we were dealing with white mold (see above), until the description of yellow, mustard-seedy sclerotia was given. We requested a sample be sent in, and confirmed the master gardener's diagnosis.

Finding this pathogen was a real treat. For a northern plant pathologist, it's a happy surprise that you may see from southern nursery stock, once in a decade, and usually only on annual bulbs. Adding to our surprise was the fact that this "tropical" fungus appears to have successfully overwintered in Minnesota! In fact, most "experts" said it couldn't happen. This fungus was found in the master gardener's yard the previous year on daylily, and had now spread to hosta, astilbe and iris. The fact that it spread isn't shocking (its not called The Fungus that Ate the South for nothing). The fact that it survived last winter is!

Mycelial growth and sclerotia Photo credit: Janna Beckerman

The key symptom of southern blight is crown rot. Profuse hyphal growth, developing quickly into mycelial fans is a key sign. Within days, sclerotia form within the mycelial fan. Sclerotia begin as white fungus balls that look like mustard seeds as they mature. Unlike white mold caused by Sclerotinia spp., sclerotia occur on the outside of the stem, and can form a crust surrounding the base of the plant.

In the white stage, water droplets form on the fungus balls. These droplets contain high concentrations of oxalic acid, which kill plant cells in advance of the fungus. This may explain how S. rolfsii has a host range of over 500 species of plants! In fact, southern blight affects nearly all field crops except grains like wheat, oats, corn and sorghum. One reference refers to susceptible ornamentals as "too numerous to list." Fungicide use for control in the home landscape is limited. Fortunately, some success has been achieved by increasing the organic content of the soil and by application of nitrogenous fertilizers.

Is this an isolated event? The answer is probably not. The fungus, S. rolfsii, is probably in numerous locations, unnoticed, unrecognized or misdiagnosed. Kudos to our master gardener (who requested anonymity!) for her diagnostic skills. In the meantime, she is looking for suggestions on types of ornamental broomcorn to plant!

Test your diagnostic savvy monthly with Disease Watch at: http://www.extension.umn.edu/projects/yardandgarden/PlantPathWeb/Plpa.htm

MPR Goes to the Arb
Beth Jarvis, Yard & Garden Line

Arb garden. Photo credit: Beth Jarvis

Horticulture will be the hot topic when Katherine Lanpher's Midmorning on Minnesota Public Radio (MPR) broadcasts live from the Minnesota Landscape Arboretum (MLA) Friday morning, August 3. The special broadcast will be run from 9 a.m. to 11 a.m.

Anyone wishing to attend can get in free from 8 a.m. to 11 a.m. by mentioning MPR at the gate. The broadcast originate from the Morgan Terrance, behind the Snyder Building. In case of rain, the broadcast will be held in the Snyder Building Auditorium.

Scheduled guests during the first hour, include: Peter Olin, MLA Director, who will speak on what's happening at the Arb and future plans. Nancy Rose, Research Horticulturist, will speak on woody plant research and plants for late summer interest. Deb Brown, Extension Horticulturist, Yard & Garden Clinic, will answer gardeners' questions throughout the program.

Growing Herbs? Try Herb Butter
Deborah Brown, Extension Horticulturist

Chives. Photo credit: Beth Jarvis

If you're growing herbs in your garden, but aren't sure exactly which flavor each will lend your dishes, you might be interested in mixing up some small batches of herb butter or margarine so you can sample them.

It's a really easy recipe: Use two tablespoons of a chopped fresh herb to one-half cup of slightly soft butter or margarine. Pick the fresh herbs just before you're ready to use them. Wash them gently in cool water, then pat them dry with a soft rag or paper towel. For best flavor, don't cut them until the last minute. Cream each herb into its own little container of butter or margarine, adding a few drops of lemon juice.

Cover and refrigerate the mixtures, but allow them to soften at room temperature before you use them so the herbs' flavors have an opportunity to develop fully. Try the herb spread on bland crackers (water biscuits would be ideal) or crusty French bread. You're sure to enjoy comparing the distinctive taste of the different herbs. This is also a great project to do with children.

Grand Rapids Hosts Hort Night
Beth Jarvis, Yard & Garden Line

The North Central Research and Outreach Center (ROC, formerly called experiment station) in Grand Rapids will host a Horticulture Day on August 29, from 2 p.m. to 6 p.m. It's free and open to the public. For directions to the ROC, go to http://ncroc.coafes.umn.edu/default.htm

See what's going on!

Those Little Black ‘Bugs' in Homes
Jeff Hahn, Assistant Extension Entomologist

Strawberry root weevil. Photo credit: Jeff Hahn

Small, pear- or bulb-shaped, hard-shelled ‘bugs' found in homes during July are strawberry root weevils. They are black to reddish-brown in color with very small punctures on their wing covers. People sometimes describe these insects as looking like wood ticks. Although both move slowly and are similar in size, ticks have eight legs while strawberry root weevils possess six legs and two antennae.

The larvae are legless grubs that live in the soil, feeding on the roots of various plants, such as arborvitae and other evergreens, strawberries, and brambles, like raspberries. They emerge as adults in mid- to late June. Unable to fly, strawberry root weevils walk into homes, apparently seeking shelter from dry summer weather. Because they are so small, they have little trouble finding small spaces around the foundation, doors, under siding and similar places where they enter homes.

Once inside, strawberry root weevils are attracted to sources of moisture and are commonly found around sinks, basins, tubs, and toilets. This author even found one on his toothbrush (fortunately before brushing). They are also commonly found on walls and on the floor. These weevils are harmless to people, our food, clothes, furniture, and other property and are just a nuisance.

Because of the harmless nature of strawberry root weevils, tolerate them as much as possible. When they are found indoors, remove them by hand or with a vacuum. Insecticides are not necessary or suggested. If you are finding large numbers in your home and wish to control them, first try to caulk and seal any obvious cracks or spaces around the outside of the home. Unfortunately, this is much easier said than done as it is usually very difficult to successfully exclude these small weevils.

You can more effectively keep out strawberry root weevils with an insecticide application. Products containing permethrin and bifenthrin will effectively kill weevils. Choose an insecticide that is labeled for application around the outside of buildings. You may also wish to hire a professional pest control operator to treat your home. Keep in mind that strawberry root weevils are only active until the end of August or early September and then go away on their own.

Stable Flies
Jeff Hahn, Assistant Extension Entomologist

House fly and stable fly. Note mouthparts. Photo credit: Dept.  of Entomology

What's looks like a house fly and bites, especially around the ankles. The answer is a stable fly and they have been common in some areas of Minnesota. Sometimes called biting house flies, they are about 1/4 - 3/8th inch in size and gray with four black longitudinal stripes. Instead of sponging mouthparts, like a house flies, stables flies possess a long, bayonet-like proboscis that they use to feed on the blood of mammals, including people, dogs, cattle, and horses.

Adult females lay on average close to 400 eggs in moist, decaying organic matter, such as urine-soaked straw and other soiled animal bedding, decaying grass clippings, poorly managed compost piles, or other decaying vegetation. However, they are rarely found in fresh manure. They prefer breeding sites that are loose and not compact. The larvae go through three stages, developing in about nine days before pupating. Adults hatch about two weeks later.

Unfortunately stable flies are very difficult to control. Repellents and protective clothes are partially effective in controlling stable flies. Sanitation of potential breeding areas can help but stable flies are strong fliers and can invade your yard from outside your property. Dogs kept outside can be protected by being placed inside a screened kennel.

What Are Those Red Bugs in Your Garden?
Jeff Hahn, Assistant Extension Entomologist

Many generations of boxelder bugs. Photo credit: Jeff Hahn

Many people are finding small, red, beetle-like or bug-like insects in their gardens or on the sides of their homes. These are boxelder bugs. Although people generally recognize the adults, most of the insects that are seen are immature which are less recognizable. They look similar to the adult only smaller. They are range in size from 1/16th inch up to ½ inch when they are full grown. Immature boxelder bugs are bright red when they first hatch. As they get larger, they appear to be red and black and they begin to develop black wing pads.

Boxelder bugs feed primarily on boxelder seeds and occasionally on maple seeds. They have also been known to feed on a wide assortment of other plants, although this not considered typical. Despite their presence on hostas and garden plants, they do not appear to be damaging them. If you do not see any injury, control isn't necessary.

If boxelder bugs do appear to be feeding and damaging plants, they should be easily controlled with an application of insecticidal soap. To be effective, insecticidal soap must come in direct contact with the insects. Insecticidal soap doesn't have any residual activity and you may have to repeat the application. Treating the boxelder bugs in your garden will no impact on how boxelder bugs you see this fall.

Dobsonflies
Jeff Hahn, Assistant Extension Entomologist

Female dobsonfly. Photo credit: Jeff Hahn

Three inch long, brown insects are probably dobsonflies. They also have long filamentous antennae and conspicuous mandibles. In fact, males have mandibles up to 3/4 inch long, making them look quite fierce and dangerous. Fortunately they do not bite people. The males use their mouthparts for fighting other male dobsonflies.

Dobsonflies are often associated with water as the immature dobsonflies, known as hellgrammites, are found in streams. However, adults are attracted to lights and can be found a distance from water. Dobsonflies are harmless. They are just a curiosity and no control is necessary.
Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm
Editorial Notes

One view at Noerenberg. Photo credit: Beth Jarvis

Noerenberg Memorial Gardens is my favorite late summer garden. If you've never been there, do try to visit soon. Directions, etc. are at: http://www.hennepinparks.org/parks/park.cfm
Arla Carmichael and her crew do a lovely job of garden design and maintenance.

Recently a Hennepin County gardener, who lived in Connecticut for 20 years, wrote. She's concerned about Japanese beetle spreading into Minnesota. She said:
"I ... ripped out my rose bushes (many), had purple coneflowers without petals, had bags and bags of beetles in those traps, and replaced my backyard lawn twice. I think Minnesotans will want to try and approach this cautiously and responsibly, which we did....but milky spore does NOT work, traps don't even begin to control them, and here in MN we don't have enough time in the fall to truly replace a whole lawn! I don't like to advocate pesticides, but I really don't know what other choice there is. ... many Minnesotans ... don't believe the damage I describe. But it is truly devastating when they land and live on your yummy turf. Raking your whole lawn up in the fall with the maple leaves is really horrifying."

I did some poking around and in addition to the new Extrension pub on the subject http://www.extension.umn.edu/distribution/horticulture/DG7664.html,
I found:
http://www.pueblo.gsa.gov/cic_text/housing/japanese-beetle/jbeetle.html
http://www.ag.ohio-state.edu/~ohioline/hyg-fact/2000/2504.html
http://people.mw.mediaone.net/cappaert/bc/jbsurvey.html

My reading indicates milky spore doesn't work in some areas Various types of biological control are discussed in the above listed websites.

Speaking of lawns, in the next issue, Bob Mugaas, Extension's "Turf Guru" will be writing about fertilizers, whether organic or synthetic is truly superior plus other thoughts he may have on the subject.

Mary Meyer will be sharing "What"s New in Ornamental Grasses" with us a bit later. It will be in plenty of time for winter catalog dreaming and garden planning. Also in time for next winter, Doug Foulk, Ramsey-Washington, will talk about pears, what to know and how to grow. I'm also lining up articles on other plant breeding projects and will give you an inside look as they are available.

Please feel free to cut and paste any of the articles for use in your own newsletters. All we ask is that you give our authors credit.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/yardandgarden/. Our home page has clickable links to most of the components of the Yard & Garden Line, such as Bell Museum of Natural History, INFO U and the Soil Testing Lab.

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Thursday of every month at 10 a.m. Katherine Lanpher hosts the program that is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations.

If you have gardening questions, please call the Yard & Garden Line at (612) 624-4771.

If you would like to receive an e-mail reminder when the next issue of the Yard & Garden Line News is posted to the web, just send an e-mail to: listserv@lists.umn.edu (note: the second E in listserve is omitted), leave the subject line blank, then in the body of the message, type: sub yglnewslist
or to unsubscribe, enter: unsub yglnewslist

Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator


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