Yard & Garden Line News Volume 4 Number 9                                                               June 15, 2002

Features this issue: Blotchy Hosta Blight Maple Anthracnose My Spider Senses Are Tingling Seedcorn Maggots Phosphorus Lawn Fertilizer Becomes Hot Issue Phosphorus and Phosphate Confused? Putting Down Roots Editorial Notes

Blotchy Hosta Blight
Janna Beckerman, Extension Plant Pathologist

Symptoms of hosta anthracnose include large, spreading lesions down the leaf vein.

A key sign is the black fruiting bodies. Photos: Janna Beckerman

Hostas recently supplanted daylily as the number one perennial grown in the United States. Reasons for hostas' continued popularity include ease of care, lush growth and disease resistance. Whenever a plant is "discovered," disease resistance is often touted. Its only when the plant enjoys widespread propagation, like hosta, that disease problems become apparent. This year, many gardeners are reporting foliar blotching. The appearance of this blotching is consistent with some frost that developed in late May. However, dieback should stabilize and not worsen, if this was an environmental affect. In other situations, the foliar problems are worsening and spreading to new leaves, suggesting a biotic agent of disease. Although we don't normally see anthracnose on hosta until later in the season, it is apparent that wet weather has created a condition that favors hosta anthracnose. It is also possible that frost damage has injured leaves, and the fungus that causes anthracnose is the first to invade.

Anthracnose is a fungal leaf disease. Symptoms of anthracnose infection include irregularly-shaped, white to tan spots on the leaves. Some hostas, in response to infection, seem to produce a spreading dark green lesion that looks like frost damage. Usually a brown border surrounds the affected area. This border may or may not have a yellow (chlorotic) halo. The spots become torn and give the leaves a tattered appearance. If you examine the leaves with a hand lens the day after a rain (or place the leaves in a moistened paper towel in a jar overnight), you can see little black hairs (called setae) of the fungus sticking out of the fruiting bodies. The causal fungus is Colletotrichum spp., and the setae are a key diagnostic sign of this disease. Because this disease is common in warm, wet conditions, good plant spacing is a key cultural control strategy. Allowing the plant to dry prevents the fungus from germinating and infecting new leaves. Removing and disposing of infected leaves may be enough to control this problem in smaller plantings.

If the disease is a chronic problem, or too many hostas are affected, fungicide use may be warranted. Copper fungicides are labeled for control of this problem in home settings. Because fungicides labeled for control of hosta anthracnose are protective (they prevent further disease and do not "cure" current problems), begin spraying when leaves begin to emerge and repeat throughout the wet season. In the fall, carefully remove the leaves prior to any mulching, to reduce the inoculum and prevent infection occurring next year!

Maple Anthracnose
Janna Beckerman, Extension Plant Pathologist

Key anthracnose symptoms include lesions that work down the leaf vein and into the petiole. Photo credit: Plant Pathology Dept.

This terrible weather has made for an interesting spring, if you are a plant pathologist. In addition to our yearly outbreak of ash anthracnose (see last year's article at: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-June0101.html#ash), we have maple anthracnose, too!

Anthracnose is a generic name for a group of diseases caused by several different fungi that cause similar symptoms, which include:
* Defoliation: repeated loss of leaves over several successive years weakens the tree and predisposes it to borer attack and winter injury

Careful examination of fallen leaves will reveal lesions that involve the leaf veins and work its way into the petiole of the leaf.

* Bud death: which stimulates the development of many short twigs or "witches' brooms (as shown on dogwood).

Yearly defoliation due to recurrent anthracnose can lead to the development of witches' broom (witches' broom shown on dogwood). Photo credit: Chad Behrendt

Each fungus has a different host, which means the anthracnose on your ash isn't going to infect your maple or your oak (and vica versa). In Minnesota, it occurs most commonly and severely on ash, sycamore, white oak, walnut and maple, all of which can be severely defoliated. It is believed that the fungi are producing hormones that cause the leaves to abscise or fall off prematurely. As the fungus grows, lesions expand and grow together, to create a more characteristic anthracnose lesion, that works its way down the midvein of the leaf, into the petiole (leaf stem) and eventually into the branch. Lesions color is variable, from tan to dark brown on leaves. Branch cankers are small and somewhat football-shaped. Often times, defoliated branches will produce new shoots in midsummer, another symptom of this disease.

When the infected tissue gets wet, the fungal fruiting bodies (which can be seen with the aid of a magnifying glass) produce numerous spores. These spores allow the disease cycle to repeat itself as weather permits. Long, rainy seasons, like the spring of 2002, is climatically favorable for anthracnose reproduction.

Management of any anthracnose requires several approaches and require that you maintain tree vigor:
* Fertilize
* Water
* Mulch

Because the tree may releaf, and in the process use its carbohydrate reserves, it is very important to maintain tree vigor and prevent the tree from declining and keep the nuisance problem of anthracnose from developing into a tree killer.

* Remove and dispose of infected foliage and cankered branches by raking and pruning.
* Good sanitation reduces inoculum

* Fungicide use is only necessary if severe defoliation has occurred in three of the last five years.
* Thiophanate-methyl (Cleary's 3336) and Chlorothalonil (Daconil 2787) are labeled for use
* Spray periods last from May through June when weather is cool and wet.

Anthracnose is ugly but it needn't be fatal. By following the above management strategies, your maples should recover and provide the shade you desire for years to come. Keep in mind that there are other diseases such as Taphrina which may be mistaken for anthracnose. We'll be discussing Taphrina in the next issue.

Please check out the new diagnostics web pages at
http://www.extension.umn.edu/projects/yardandgarden/diagnostics/

My Spider Senses Are Tingling
Jeff Hahn, Assistant Extension Entomologist

Funnel web and spider. Photo credit: Jeff Hahn

Perhaps the popularity of the movie Spiderman has people thinking about eight-legged creatures more often than usual. But whatever the reasons, spiders have been one of the more common questions we've received this spring. There has been two types of questions – too many spiders in their house and finding spiders that they believe may be dangerous.

Although spiders are more common at the end of summer, some people experience unacceptably high numbers all season. The number of spiders a person may tolerate of course is variable. For some, the threshold is quite low. Despite that, remember that spiders are generally harmless to people and are usually only a nuisance.

A home's location is also a factor in how many spiders are seen. People living in rural or suburban areas, especially when they are close to water (lakes, streams, rivers etc.) are going to naturally see more spiders. These type of environment generally supports higher insect numbers. Since insects are a primary food source for spiders, spiders numbers are higher in these areas.

Fishing spider. Photo credit: Jeff Hahn

If it is desirable to reduce spider numbers, first start outside. Make the environment less favorable for spiders and their insect prey . Move brush piles, wood piles, accumulations of leaves, and other potential harborage areas near the home away from the foundation. Also keep long grass and weeds near buildings cut down. Remove webs and crush egg sacs on the outside of buildings as they are seen.

Indoors, clean up areas where papers, boxes, and other objects have accumulated. If you find just one or two spiders, collect them in a jar and release them outdoors. Or you can easily kill them with a broom or rolled up newspaper. Remove spider webs (a vacuum works great for this) and crush egg sacs. Particularly check corners, near the floor as well as around the ceiling, and around windows. Place sticky traps (like a Roach Motel) in areas where spiders are common. This is especially effective for hunting spiders.

Although insecticides can be used to supplement these nonchemical methods, they should not be used routinely. Apply products only when spiders are particularly bothersome. Insecticides are most effective when used outdoors to prevent spiders from entering homes. Choose a product that is labeled for use around the exterior of buildings. Products containing permethrin and bifenthrin are often labeled this way. Particularly treat nooks and crannies where spiders are more likely to hide. Insecticides are a short-lived control measure and their use is more effective when combined when sanitation and physical removal.

Sometimes the issue for home dwellers in not high spider numbers but one or a few spiders that they believe are dangerous. This is particularly true when they find a large sized spider. A common large-sized spider found in the summer is the fishing spider. They have a body length up to one inch long and measure several inches across including their legs. People may also see wolf spiders which are similar in appearance and habits. Despite their size, these spiders are not dangerous to people.

People occasionally believe they have found a brown recluse. The native range of the brown recluse is the south central area of the U.S., though they can be accidently transported outside of that area. Brown recluse are rarely, if ever, found in Minnesota. There is one report of a brown recluse from Lake county in 1953. Brown recluse specimens have never been verified in the Twin Cities.

Wandering spider. Photo credit: Jeff Hahn

Despite dozens of reports of brown recluse each year, all suspected specimens turn out to be common native spiders. Recently, a homeowner believed he was finding brown recluse in home in the Twin Cities. He submitted several house spiders and a wolf spider, both types very common in Minnesota.

Sometimes people actually do encounter an exotic spider species. Another homeowner claimed to have found a type of wandering spider. It had been discovered in a grocery store on bananas. It turned out he was correct. The spider was not aggressive and nobody was bitten. This was fortunate as wandering spiders are quite venomous.

Nearly all spiders that people suspect to be dangerous turn out to be relatively benign species native to Minnesota. Rarely, exotic spiders can be found in the state, usually associated with produce. If there is ever any doubt about a spider that you find, submit a sample to an expert for identification.

Seed Corn Maggots
Jeff Hahn, Assistant Extension Entomologist

Seed corn maggot adults on sticky trap. Photo credit: Jeff Hahn

Seed corn maggot adults have been quite common in early June. Adults are about 3/16 inch long, grey and resemble house flies. The maggots feed on decaying vegetation and other organic matter but are also known to attack germinating seeds of various plants. In agriculture, they are pests primarily in beans, soybeans and peas but may also may attack corn, onions, curcubits, crucifers, and other crops.

They are occasionally a pest in home gardens. Their injury is generally worse during cool, wet springs, especially when the soil is high in organic material. Sometimes the adult flies may cause concern in gardens and yards just by their presence. They move deliberately and sometimes can be a minor nuisance when landing on people. Gardeners setting out sticky traps to monitor pests may find large numbers of these flies captured on the glue.

It is common for these flies to become infected by a fungus that eventually kills them. This is especially common during wet springs. You can identify fungus-killed flies because their bodies and legs are often at odd, awkward angles. If you look closely you can sometimes see whitish fungal filaments coming out of the fly's body. No control or action is necessary. Despite the circumstantial evidence, these flies are not responsible for sucking out sap, making holes in leaves, creating dead twigs or other damage to plants.

Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm

Phosphorus Lawn Fertilizer Becomes Hot Issue
Daniel Huff, Coordinator, Dakota County Environmental Education Program
Ron Struss, Water Resources Education, University of Minnesota Extension Service

Stream-side garden. Photo credit:  Beth Jarvis

In past years a number of Minnesota communities have restricted the use of phosphorus fertilizer on established lawns. Last session, the Minnesota legislature overwhelmingly passed SF1555, a law that will affect the use of phosphorus lawn fertilizer throughout the state. Why these restrictions and what is the problem with phosphorus?

Phosphorus, along with nitrogen and potassium, is an essential plant nutrient. A plant lacking in any of these three essential nutrients will suffer in its growth and health. This is why people use fertilizer. Fertilizer contains various amounts nitrogen (N), phosphorus (P) and potassium (K). Nitrogen greens up plants and contributes to their growth; phosphorus is important in a plant's metabolism; potassium is needed for a plant's structure. In order to increase production we use fertilizer to boost plant growth and performance. Farmers use fertilizer to increase the productivity of their crops, thus producing more food from less land. Homeowners may use fertilizer to keep a healthy lawn or brighten up their rose bushes. Fertilizer and phosphorus in themselves are not bad things. However, misuse and overuse can have unintended and detrimental consequences.

Phosphorus that washes into our lakes and rivers with rain and snowmelt is a major cause of water pollution in Minnesota. Aquatic environments are delicately balanced systems. Change the balance by adding extra fertilizer and you create problems. Phosphorus in lakes and rivers causes algae to grow out of control. This algae chokes off other aquatic life, blocks out light, and results in low dissolved oxygen levels in the water. With too much phosphorus the land of sky blue waters becomes the land of green slimly waters.

Ironically, one of the sources of this phosphorus comes from adding it to our lawns, even though our lawns usually don't need it. Over 75% of established lawns in the seven county Twin Cities area do not need more phosphorus. Phosphorus tends to stick around in the soil, making most lawns rich in phosphorus from past fertilization. Adding more does nothing for your grass, but potentially causes harms to your nearest lake, wetland, or river.

New state restrictions on the use of phosphorus lawn fertilizer use do not go into effect until January 1, 2004. After that date, use of lawn fertilizer will be restricted to:
· 0% phosphate content in the seven county Twin Cities metro, and,
· 3% or less phosphate content in other areas of Minnesota
There are exceptions to these restrictions. They do not apply to agricultural or garden fertilizer and allow use of lawn fertilizer with higher phosphate content on newly seeded lawns or when soil testing shows a phosphorus need.

Starting August 1, 2002 is a part of the state law that requires all fertilizer spilled or spread on paved areas (streets, sidewalks, driveways) to be cleaned up and applied to the lawn or re-bagged.

What can you do? Buy zero phosphorus fertilizer (look for a middle N-P-K number of zero). If you think your lawn needs phosphorus, get a soil test. Forms and information on taking a home lawn soil sample are at: http://soiltest.coafes.umn.edu/. Or you can request forms by calling the Soil Lab through the Yard & Garden Line at 612-624-4771 and selecting option 4.

Most importantly keep all sources of phosphorus from washing away and down nearby storm drains. Storm drains lead to lakes and rivers. Other sources of phosphorus include leaves, grass clippings, pet waste, soil and organic fertilizer. Sweep up, rake up and scoop up! If it's on the pavement now, it's in our local waters after the next rainstorm.

Phosphorus and Phosphate Confused?

You might be confused by the use of "phosphorus" and "phosphate" when reading about lawn fertilizer.

Phosphorus is the actual plant nutrient. However, by age-old convention, phosphorus content of fertilizer is measured in terms of phosphate (P2O5), a material that is 43% phosphorus.

Fertilizer bags are labeled with three number that give the nitrogen (N), phosphorus (P2O5), and potassium (K2O) content in terms of percent total weight. The number for nitrogen is first; phosphate is in the middle number, and the number for potassium comes last.

Putting Down Roots
Cliff Johnson, Carver/Scott Master Gardener

Woodland landcapes don't  just happen. Photo credit:  Beth Jarvis

Wooded lots change over time, for better or for worse In the real estate business, the term "wooded lot" is magic. Everybody, it seems, wants to live on a wooded lot. I have a hunch, however, that quite a number of folks who live on wooded lots don't spend much time contemplating how their wooded space is going to change for better or for worse" over time.

And the fact is, wooded lots don't change for the better unless woodlot managers intervene and manage the space. "Letting Mother Nature take her course" isn't usually a good idea in a woodlot. I live on an acre and a half that is mostly wooded. I have learned that, left on its own, a woodlot can quickly develop bad habits.

One dramatic example is the almost-overnight invasion of noxious, non-native plants such as buckthorn. The index finger on my right hand presently feels like sandpaper and is creased with imbedded soil--the result of hand-pulling hundreds of young buckthorn seedlings that appeared out of nowhere this spring. Where did all the buckthorn come from? Birds planted them, one tree at a time, as the birds perched in overhead tree branches or dropped their biological greetings during flyovers. My bumper crop of buckthorn seedlings ranges in height to 3 ft. It's critical that I pull them out, roots and all, to prevent a total takeover of the understory. Buckthorn can infiltrate a woodlot in a few short years unless the plants are completely removed.

Two other forms of intervention I spend a lot of time at are pruning and maintaining a balance of tree species. I want a variety of species because disease can quickly wipe out a monoculture of trees. It's happened with American chestnut, elm and many stands of seemingly healthy oak. My dining room window looks out on a back yard of trees and a pond.

Ten years ago this space was occupied by two giant bur oaks and dozens of smaller trees of many species: elm, red and bur oak, cherry, plum, apple and basswood. Gradually I came to realize that not all these trees could grow to maturity in the spots in which they had taken root. Some, actually most, would have to be removed to allow space and light for the most desirable trees I hoped to look out on and appreciate in the decades ahead.

Linden/basswood flowers. Photo credit:  Beth Jarvis

My overall objective is to nurture multiple generations of desirable and primarily native trees and shrubs and remove all undesirable species. This aspect of woodlot management is like the parenting concept of "tough love". It's hard to do but it's best for the child over the long haul. Deciding which trees to remove requires having a clear picture of your objective. Five or 10 years from now, are you hoping for a dense forest wall of trees? Do you want trees and shrubs of different heights and textures with a mix of blooms and fruit? Is your goal to attract wildlife? Since I didn't want the dense forest look, I decided the basswoods had to go. Basswoods grow very fast and wide and tall. Already, some of the basswoods growing outside the dining room window had trunk diameters of 8 in. or more. "You mean you intend to cut down all those huge trees with the smooth gray bark and sweeping branches of large, glossy leaves?" visitors would ask me incredulously. "That's my plan," I would say, adding that I also planned to cut down several large elms, oak and ash. "Well, I think you're nuts," they'd respond.

It's been almost two years since I removed the basswoods. In their place, I planted two crabapple, two Japanese tree lilacs, 25 arborvitae and several rhododendron. I also moved in a half dozen young Pagoda dogwood from other spots. I left in place several oak and apple trees and highbush cranberry shrubs. I won't deny that the view from my dining room window these past two years has been more open and sparse than I would have liked. Certainly the view is more open than the dense, dark wall formed by the basswoods.

Think about this, however: Every year for the next decade or two the view will improve, rather than grow darker and more oppressive. The crab apples and tree lilacs will grow to 20-25 ft. and bloom with pretty flowers. The winter view will be enhanced by the arborvitae and by the winter fruit on the crabapples and highbush cranberries.

Do you have a clear picture of what your woodlot will look like a decade from now? Are there invasive, non-native woody plants that are crowding out your more desirable trees and shrubs? If you're not sure and would like answers to these questions, you may want to consult a landscaper or arborist. One thing I know for certain about woodlots: They don't stay the same. Whether your woodlot evolves for better or for worse depends on the decisions you make now.

Editorial Notes

Ripening blueberries. Photo credit:  Beth Jarvis

Looks like summer is finally here! My blueberry bushes are loaded with green fruit which should be ripe in a month or less.

I asked the Master Gardeners for story ideas and got some great ones. Coming up for mid-July, we'll hear from Nancy Rose who works on woody plant introductions. I have other ideas but am always interested to hear from you, as well.

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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