Yard & Garden Line News Volume 1 Number 12                                                               October 1, 1999

Features this issue: Mycorrhizae--the Friendly Fungi Tulip Time New Garden Calendar Available Accidental Invaders Clean Up Old Iris Plants Snow-on-the-Mountain Leaf Spot This Season's Unusual Disease: Poppy Anthracnose Storage Rot of Potato Editorial Notes

Mycorrhizae--the Friendly Fungi
Rhoda Burrows, Graduate Research Assistant, Dept. of Plant Pathology

Showy Lady's Slipper Photo credit: U of MN Extension Service

When you hear "fungi", what comes to mind? Mushrooms and toadstools, or mold and mildew? Or plant diseases such as Dutch elm and late blight? Did you know that most plants have beneficial fungi in their roots? These fungi extend from the roots into the soil, and help supply the plants with nutrients such as phosphorous and nitrogen, in exchange for carbohydrates from the plants. This mutually beneficial relationship is known as a mycorrhiza, which translated literally means 'fungus-root.'

There are several different kinds of mycorrhizae, depending on the plant host. Most trees and shrubs in Minnesota form "ectomycorrhizae" (ecto- = "outer"), in which the fungi build a sheath around the roots, and penetrate between but not into the root cells. Since most ectomycorrhizal fungi form mushrooms as their means of reproduction, you have probably seen many of these fungi when walking through a forest after a rainy period. Many trees and shrubs need these fungi in order to thrive, or even to survive.

Orchids, including natives such as the Showy Lady's Slippers, are dependent on their mycorrhizal fungi for early growth because their tiny seeds don't contain food reserves for the newly-germinated plant. Unlike other mycorrhizaes, the orchids don't supply these fungi with carbohydrates - instead, the fungi supply the orchids with energy as well as nutrients obtained from decaying organic matter. In fact, it's unclear whether the fungi receive anything at all from the plants in return for their contributions.

Big Bluestem Photo credit: Beth Jarvis

Most Ericaceous plants, such as blueberries, cranberries, and Rhododendron, form "ericoid" mycorrhizae, where the fungi grow into the cells of the root epidermis (the outer tissues of the root).

And finally, 80% of plants form a type of mycorrhizae known as "endomycorrhizae" (endo-="inner"), in which the fungal hyphae do enter inner root cells, altering them to form "arbuscules", which are specialized nutrient exchange surfaces. It is from these structures that these fungi get their name "Arbuscular mycorrhizal fungi", or "AMF". Grasses, wildflowers, and most garden plants (except those in the cabbage family) form this type of mycorrhizae. Fossil evidence indicates that AMF were present when plants first colonized land, which may help explain why they are so common. Many tallgrass prairie species, including big and little bluestem grasses and wildflowers such as butterfly weed, would probably not survive without these minute partners in their roots.

Butterflyweed. Photo credit: Beth Jarvis

There are a number of commercial companies that will sell inoculum to the concerned homeowner for their plants. Will it help? That depends. If you are planting trees in an area where there are none, inoculation with the appropriate ectomycorrhizae may be of benefit. If you are trying to germinate orchid seed, their fungal partners will need to be supplied. Ericaceous plants may benefit as well. However, few field studies have shown benefit from spreading AMF inoculum on your yard or garden, perhaps because these fungi tend to be fairly common and are likely to be present already. Also, if you fertilize heavily with phosphorous, or use certain soil fungicides, you are unlikely to see much benefit from applying AMF, because their effects will be masked, or they will not do well. However, if you start your own seedlings in a sterile or artificial soil, inoculating them may help them survive transplanting and increase their resistance against soil-borne disease.

Tulip Time
Deborah Brown, Extension Horticulturist

Spring bulbs. Photo credit: Deb Brown

What would spring be without colorful tulips? Following our typically drab late winter landscape, replete with dirty melting snow, they're exactly what the doctor ordered. But if you want some beautiful bulbs blooming in your yard next spring, you've got to get busy soon. Mid to late October is the perfect time to plant them.

It's easy to create a showy display for next spring. However, in this climate, tulips tend to diminish annually after their initial bloom. If you expect your tulips to prosper and return for years to come, you can't just plant 'em and forget 'em. On the other hand, a little attention to detail will ensure your long-range success -- unless Mother Nature sends us some truly abominable weather somewhere along the line.

Shop Smart

Bargain hunters, beware: smaller, cheaper tulip bulbs will not deliver the display you can achieve with larger, more costly ones. Nor are they as likely to perform well for more than the first season or two.

You should be able to buy your bulbs locally at a nursery or garden center or send away for them with equally good results. You may find a wider selection available by mail, but when you buy locally you can inspect the bulbs -- often, individually. Look for big firm bulbs without rots, bruises or soft spots. The presence of papery brown skin -- or its absence -- is of no consequence. Nor are areas of blue mold (penicillium), provided the bulb feels firm.

Pick a Good Site

Choosing a favorable site is an important first step in growing tulips well. Although they'll bloom in a shady spot the first year, you really need to find a sunny place if you expect more than foliage, subsequent springs. As with most sun-lovers, full sunlight is definitely best.

(On the other hand, there are some situations where it makes perfect sense to treat tulips as annuals -- when all you have is shade, for instance -- or when you can't afford the garden space to allow tulip greens to ripen and die down naturally each year.)

Don't plant tulips -- or any other bulbs, for that matter -- beneath downspouts or in low lying parts of your yard where moisture collects. Those fleshy bulbs are prone to rotting if the soil stays too wet. To thrive, tulips must be planted in soil that drains decently.

Prepare the Soil
If your soil is extremely sandy and water runs right through it, work a little organic matter into the upper ten or twelve inches before you plant. Mix fully decomposed compost or baled, dry peat into the existing soil. Though neither provides much in the way of nutrients, they help prevent any fertilizer you may apply from washing away.

Should you have no choice but to plant in heavier clay soil, dig down ten or twelve inches and incorporate lots of coarse sand into the soil before replacing it.

Take Time to Plant Correctly
The easiest way to plant lots of tulips is to dig a large hole, scatter fertilizer or "bulb food" along the bottom, then add an inch or two of soil. Set the bulbs exactly where you want them (pointed side up), then replace the soil you removed. Firm the soil gently and water the area thoroughly.

Take your soil type into account when you decide how deeply to plant tulip bulbs. When not planted deeply enough they're more vulnerable to winter injury if snow cover is skimpy. They're also more likely to multiply after the first year. This sounds useful, but in reality it means for each good-sized blooming bulb you planted, you end up with lots of smaller non-bloomers.

In light, sandy or well-drained soil, position your tulip bulbs so their tops are seven or even eight inches below the soil surface. If your soil is heavier and more clay-like, reduce that amount to four or five inches.

Forget Rows
To maximize their impact, plant your bulbs about six inches apart in clusters or drifts, or -- if you can afford it -- large masses of the same variety. You'll find it easier to space odd numbers of bulbs than even numbers.

Not all tulips bloom simultaneously; some are early varieties, some, mid-season and some only bloom in late spring. To create a truly dazzling combination you must choose tulips that flower at roughly the same time.

It's probably best to concentrate on early or mid-season varieties. Late bloomers may droop and lose their petals within a couple days if we have unseasonably hot weather, late May or early June.

Care After Planting
Continue to water the bulbs every couple weeks if rainfall is sparse. Once the soil begins to freeze, mulch the area with several inches of leaves, straw or evergreen boughs. The mulch will protect your bulbs from severe cold, but more important, it will help keep them dormant in the face of early warm weather.

Each spring, fertilize your tulip bulbs just as their leaves begin to emerge from the soil. After you've picked off the faded flowers, resist the urge to remove any leaves before they yellow on their own. The longer that foliage stays green and healthy, the more food energy will be stored in your bulbs for the next year's growth.

And finally, if you intend to plant annuals among your tulips to take over as they fade, be sure to choose ones that don't require lots of watering. The bulbs will do better with moss roses or marigolds than they will with impatiens or snapdragons.

New Garden Calendar Available
Deborah Brown, Extension Horticulturist

Minnesota Gardening 2000 calendar.

Look for the calendar with masses of bold sunflowers on the cover. Minnesota Gardening, 2000 is now available in major book stores such as Barnes and Noble, garden centers including Bachman's and others throughout the state, gift shops, county extension offices, and directly from the University. (To order from the U, call 612-624-4900, metro, or 1-800-876-8636, greater Minnesota.)To preview the calendar go to: http://www.extension.umn.edu/distribution/horticulture/DG7358.html.

This is the tenth in a series of award-winning calendars published by the University of Minnesota Extension Service and Agricultural Experiment Station, and like its predecessors, it has been written by Extension Horticulturist Deb Brown, specifically for people interested in gardening and landscaping in our challenging northern climate.

In addition to beautiful photography, climate maps, and a list of practical tips each month, the year 2000 calendar features a page on growing amaryllis bulbs. There is also information about many of the different organizations concerned with helping people with their gardening and landscape questions and activities, including the address and phone number for every county extension office in the state.

Minnesota Gardening, 2000 would make an excellent holiday gift for your gardening friends and relatives. It's also a particularly nice memento for people who lived in Minnesota, but have moved away. Calendars are shrink-wrapped and spiral bound, using highest quality paper. Suggested retail price is $11.95

Accidental Invaders
Jeffrey D. Hahn, Assistant Extension Entomologist

Boxelder bug.

Cluster fly.

Elm leaf beetle. Photos: Jeff Hahn

Hackberry Psyllid

Millipede

Multicolored Asian lady beetles. Photos: U of MN Entomology Dept.

Western Conifer Seed Bug. Photo credit: Jeff Hahn

Sowbugs. Photo credit: Jeff Hahn

Late summer and fall is the time of year when many types of insects and other arthropods accidentally enter homes as they search for sites to overwinter. They are not harmful to people or cause damage to property. They are short-lived indoors and do not reproduce there. But people object to their presence and they are considered to be nuisances.

The following is a brief summary of some of the more common insects that can be expected to be seen. So far, it does not appear that any of these insects are present in large numbers this year, although we can expect to see all of them to some degree.

Boxelder Bugs: It has been 11 years since our last significant outbreak of these ½ inch long orange and black insects. Boxelder bugs feed on the seeds of boxelder trees during summer before flying to homes in the fall to seek shelter.

Cluster flies look similar to house flies but a little larger (3/8 inch long). Upon close examination, wavy yellow hairs can be seen on the sides of their thorax near their head. During summer, cluster flies parasitize earthworms. When they fly to structures, they're typically found on the upper half of buildings.

Elm leaf beetles are 1/4 inch long, oval, yellow-green with several black stripes. Once they die their color often fades to an olive or brown and the stripes may not be apparent. During the growing season, these beetles feed on elm leaves, especially those of Siberian elm.

Hackberry psyllids are very small (3/16 inch long) and gnat-like. They are a mottled brown, with small black and white spots. Despite their appearance to flies, psyllids are relatives of aphids, leafhoppers, and scales. These psyllids produce galls on hackberry leaves. They emerge from these galls at the end of summer and search for overwintering sites.

Millipedes and sowbugs are not insects but are related arthropods. Millipedes are 1 - 1 ½ inches long, dark-colored, and curl up when they die. Sowbugs are about 3/4 inch long, grayish and resemble a turtle or armadillo. They both prefer cool, dark, damp sites and often are found on the ground under stones, wood, mulch, leaves, and other objects. Millipedes and sowbugs are usually more common in the fall after we have had a wet, cool summer.

Multicolored Asian lady beetles (MALB): These lady beetles are about 1/3 inch long (a little larger than most lady beetles) and have 19 black spots on their back, although the size of the spots are quite variable. MALB also have a black 'M' on their prothorax (behind their head). These lady beetles are very beneficial because they eat aphids, but can be very annoying when they cluster in large numbers around homes. While other fall invaders first start coming to homes in August or September, MALB will be first noticed around homes in mid- to late October.

Western conifer seed bugs (WCSB), a type of leaf-footed bug, are about 3/4 inch long, brown with white markings. They have large back legs (sometimes people think they look like grasshoppers). Each leg has a leaf-like enlargement on it which is how they get their name. WCSB feed on the green cones and needles of pine and Douglas fir during summer.

There are several steps you can take to combat these insects. The best solution is to try to prevent them from coming in to begin with. Do this by exclusion. Check around the outside of your home for cracks in foundations, spaces around windows and doors, holes in screens, spaces under siding, areas where wiring comes into a building, poorly screened vents, spaces in overhangs, and other places where insects may enter buildings. Caulk cracks and other openings, screen vents, replace or install weather stripping around doors and make what ever other repairs are necessary . Although it is not possible to completely seal out all pests, you can significantly reduce their numbers by repairing obvious openings.

If large numbers of insects are present, consider applying an insecticide. Chlorpyrifos or diazinon are effective against most insects. Permethrin is particularly effective against cluster flies. For flying insects, concentrate your efforts on the south and west sides of your home; this is where these insects are most likely to be found.

For millipedes and sowbugs, you should also remove leaves, grass clippings, wood piles, stones, mulch, brick piles and other objects these invertebrates may hide under. If it is necessary to use an insecticide, make your application in a band on the ground and on the building. You can also apply granules on the ground around the foundation.

Once these pests get inside, the only practical control is to remove them by hand or with a vacuum. Insecticides are normally not necessary. Remember they are harmless and just a temporary problem. It is possible to see these insects periodically throughout the winter and again in the spring when weather is mild and sunny. You can not prevent them from coming out from the walls or other places. Just physically remove them when they appear.

Clean Up Old Iris Plants
Jeffrey D. Hahn, Assistant Extension Entomologist

Iris borer damage on foliage. Photo credit: University of Wisconsin

Adult iris borers have been active since August and September, laying eggs on old iris plants. The eggs remain there through the winter, hatching early next spring. You can reduce the number of borers that will be present next year, by removing and destroying old iris plant material and any nearby plant debris this fall.

By doing this, you remove and kill overwintering eggs, minimizing the risk of iris borers next year. You should do this even if you did not see borer damage, because there is likely to be other iris nearby which could be a source of iris borers.

The best time to do your clean-up is after the first hard frost when female moths are no longer laying eggs. If you remove the old plant material too soon, adults may still be actively laying eggs. You should burn (where permitted) or bury this material. You can also put foliage into a properly maintained compost pile.

If you've had a history of iris borer problems, you may need to apply an insecticide next spring when new growth is about four inches high. Cygon 2E (dimethoate) is currently labeled for iris borer control.

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

Snow-on-the-Mountain Leaf Spot
Chad Behrendt, Extension Plant Pathologist

Cylindrosporium on snow-on-the-mountain. Photo credit: Chad Behrendt

Snow-on-the-Mountain (Aegopodium podagraria 'Variegatum'), a popular ground cover, is often infected by leaf spotting fungi. These fungi generally cause spotting of the leaf tissue and browning of the leaves. When disease is severe, these fungi cause browning and death of the leaves and plant. Although infection begins early in the season, symptoms are usually the most obvious in late summer and early fall (August to September).

A variety of fungi infect the leaves of Snow-on-the-Mountain. Cylindrosporium sp. is one fungus recently identified by the Yard and Garden Clinic. This fungus typically causes small, brown, necrotic leaf spots. As these leaf spots develop, they spread from infected leaves to adjacent healthy leaves. Often, these small circular lesions coalesce to form larger irregular lesions. Severely infected leaves may drop prematurely. This fungus can also infect the main stem, causing death of the plant.

Symptoms caused by other leaf spotting organisms would be similar to those described above. Regardless of the exact fungus causing the problem, weather is going to play the largest role in disease severity. Like most fungi, leaf-spotting organisms are stimulated by cool, wet periods. Therefore, disease severity will be greater during wet, rainy years than dry years. Disease will also be more severe in cool moist areas, dense plantings, and heavily shaded areas.

Cultural practices that reduce the amount of available moisture and increase airflow will help reduce the severity of disease. To avoid prolonged periods of wetness, water plants early in the day. To further manage leaf spots, conduct good sanitation practices in the fall. Fungicides such as Cleary’s 3336 may be effective, but are not recommended.

This Season's Unusual Disease: Poppy Anthracnose
Chad Behrendt, Extension Plant Pathologist

One sick poppy.

Orange spore mass on stem. Photo credit: Yard & Garden

Every year the Yard and Garden Clinic receives a variety of samples. Weather always plays a large role in the number and types of diseases that occur and this year was no exception; the wet spring initiated ideal conditions for a variety of fungi to thrive. We observed many unusual samples and problems this year, but the most unusual problem was Poppy Anthracnose.

Poppies, in general, are relatively disease free. As a result, we very seldom receive samples for plant disease diagnosis. In June, shortly after the wet spring, we received a poppy sample with bending and curling of the main stem. This disfiguration caused the plant to turn brown and die. At the point of curling an orangish-pink mass of fungal material appeared. Initially this material appeared to be rust spores, but after microscopic examination the fungus was identified as anthracnose.

The orange mass of fungal material proved to be an accumulation of spores that were formed in reproductive structures called acervuli. This production of spores is an unusual event, which occurs only during prolonged periods of wetness.

Without microscopic examination of the fungal spores, diagnosis would have been difficult. To differentiate these two fungi we examined the spore size, shape, and texture. Another approach would be to check your reference materials and see if rust fungi commonly occur on poppy. Westcott’s Plant Disease Handbook does list anthracnose, but does not list rust fungi.

Anthracnose typically forms a brownish to gray colored lesion on the flower stem. Later, the fungus produces spores within the lesion. Severely infected stems curl and bend at the point of infection. It is common for multiple lesions to cause multiple bends. When conditions are severe, anthracnose can also infect the petioles and leaves of the plant.

Since, this disease is an uncommon problem, chemical control is not warranted. Sanitation and removal of infected material as soon as it appears should adequately control this disease. If chemical control is desired, a fungicide containing Cleary’s 3336 or Potassium Bicarbonate (Remedy), can be applied as a preventative spray. Other management techniques should include proper spacing to provide airflow and proper watering (at ground level) to avoid unnecessary wetting of the plant.

Storage Rot of Potato
Chad Behrendt, Extension Plant Pathologist

Verticillum necrosis. Photo credit: Plant Disease Clinic

Late blight rot. Photo credit: Plant Disease Clinic

Potato scab Photo credit: Clemson University

‘Storage rot’ is a common name given to decomposing or rotting potatoes in storage. Storage rot can be caused by a variety of different fungi and bacteria, which often enter tubers through wounds. The most frequent point of entry is through wounds created during harvest or handling. These wounds allow a variety of fungi and bacteria surviving in the soil and on the surface of the tuber to enter and infect. In addition, many organisms enter and infect tubers during the growing season. These organisms may rot the tuber during the growing season, or remain inactive and symptomless until ideal conditions develop during storage.

Once stored tubers begin to rot, these organisms grow and multiply. Fungal material and bacterial cells infect nearby potatoes causing secondary infections. These organisms then continue to spread from one potato to the next, rapidly rotting large quantities of stored potatoes.

Symptoms associated with infected potato tubers may include soft spots, brown lesions, mummified tubers, soft wet tissue, a slimy or dry texture, internal cavities, white or colored fungal growth, and bacterial ooze. Probably the most common disease causing storage rot is bacterial soft rot. This disease, caused by the bacterium Erwinia carotovora, causes a wet, soft grainy texture to occur inside of the tuber. Infected tissue is usually a cream to tan color, while the margins are usually darker. As the rot continues the tuber develops a slimy texture and a foul odor.

Another common storage rot is caused by the fungus Fusarium sp., which frequently enters through mechanical wounds. Dry rot initially appears on the surface of the tuber as small brown lesions. As the fungus degrades the tuber tissue, the surface of the tuber becomes sunken and depressed. Eventually tubers shrivel and mummify, forming dry hollow cavities within the tuber. Fungal growth is often associated with the infected tuber.

One other fungal disease that may cause tuber lesions and rot is late blight. This disease, common throughout the growing season, mainly affects the leaves and stem of the plant, but can also affect the tubers causing shallow, tan to brown colored lesions. These lesions may create a secondary avenue for other infectious agents such as bacterial soft rot.

In addition to storage rot, there are a number of diseases that cause discoloration or superficial damage to the surface of the tuber. A few of the common diseases include scab, silver scurf, and wilt. Potato scab causes a brown, sunken or pitted appearance to the surface of the tuber, but does not usually affect the internal portion of the tuber. Silver scurf, also a superficial disease, causes the tuber to develop a silver appearance on the outer skin, but does not affect the internal portion of the tuber. Verticillium wilt does cause a brown necrotic appearance within the tuber, but does not typically cause tuber rot or internal break down of the tuber.

Whether you are growing your own potatoes or buying potatoes from the market, here are a few tips to help prevent storage rot. Harvest potatoes after vine death, when potatoes are mature and the soil is cool. Minimize mechanical damage during harvest by carefully digging tubers. Before storing potatoes in a cool dark place, allow them to dry in the sun for a short period of time after harvest. Protect potatoes from direct sunlight and desiccation while storing. Keep tubers as cool as possible during storage and provide adequate ventilation. If stored in bags, make sure the bags are well vented. Finally, to help prevent tuber infections during the growing season, monitor and manage plants throughout the growing season for foliar symptoms of plant disease.

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

Part of Terrace Garden, Alexandria Photo credit: Beth Jarvis

Fall has come early this year. Even here in the banana belt of Minnesota, our first hard freeze is supposed to occur this coming weekend. We're hearing predictions for 20" more snow than normal this winter.

With the end of the gardening season bearing down on us, Yard & Garden Line News will switch to the winter publication schedule. So, this is it for October. We will publish only on the first the month from now until April. Then, we'll resume twice monthly issues.

I appreciate the story suggestions I've received. In the months ahead, we'll bring you articles on dog blight and plants that provide color in the shade. This summer, Douglas Co. Master Gardeners put plastic sandwich bags over developing apples to eliminate the need to spray insecticides. You'll also see their amazing preliminary findings in an upcoming issue.

As the garden supply catalogs begin to accumulate, we plan to provide you with timely info about apple tree rootstocks and new blueberry varieties. One of the newer faculty members, Christian Thill, will share his thoughts on selecting potato cultivars and comment whether Colorado potato beetle resistant seed potato will ever be available to homeowners again.

The garden at left is a small part of the Terrace Learning Gardens. It was developed by Douglas Co. Master Gardeners who have won a Search For Excellence Award for their efforts. It's located at the county office building in downtown Alexandria.

Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/projects/yardandgarden/.

We publish the Yard & Garden Line News twice a month during the gardening season, on the first and 15th of the month. October through March, we publish monthly, on the first.

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.

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

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.

For plant and insect questions, visit http://www.extension.umn.edu/askmg. Thousands of questions have been answered, so try the search option in the black bar at the top left of the board for the fastest answer.

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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