Yard & Garden Line News July 1, 2002

Yard & Garden Line News
Volume 4 Number 10 July 1, 2002

Features this issue:
Leaf Blister of Maple--Not Anthracnose
Friendly Flies
Ichneumonid Wasps
Bumper Crop of Bunnies
Editorial Notes

Leaf Blister of Maple--Not Anthracnose
Janna Beckerman, Extension Plant Pathologist

Taphrina created symptoms that could be mistaken for anthracnose or herbicide damage All photos:
Janna Beckerman

To tell Taphrina from anthracnose, note that Taphrina does not cross leaf veins. Lesions on left, Taphrina; lesion on right, anthracnose.

Light bloom on leaf underside and microscopic identification of the asci confirmed Taphrina. Special thanks to Sandee Gould, who diagnosed the problem!

Every plant, without exception, is susceptible to numerous foliar pathogens. Diseases that affect foliage have several common factors, which include: The need for a susceptible host, the proper environmental conditions and fungi or bacteria capable of causing disease. The disease triangle is a model to explain how host, pathogen and environment interact to cause disease. This year, we have had an unusually wet spring throughout much of the state. This moisture is occurring at the same time succulent shoots and leaves are being produced by trees and shrubs. With the proper environmental conditions (cool, wet spring) and a susceptible host (young tissue is most easily infected), any potential pathogen has the opportunity to become epidemic. We are seeing an epidemic year of foliar disease problems on maple. One disease, maple anthracnose, has exploded. Unfortunately, I suspect many people have overlooked or misdiagnosed another, more unusual foliar pathogen, Taphrina sacchari, the causal agent of leaf blister of maple.

Although leaf blister if a very descriptive name for this disease, infection has occurred so fast and furiously, that many of the infected samples do not possess the characteristic blisters. Instead, we are seeing maple leaves that have bright green veins, and black necrotic tissue in between. A key symptom to distinguish Taphrina from anthracnose is the fact that Taphrina does not cross leaf veins or work into the petiole of the leaf .

Under normal infection, infected cells develop "blisters" due to the secretion of growth regulating chemicals by the fungus. This results in abnormal cell division and enlargement giving the leaves a curled and crinkled appearance. Leaves do not normally drop, unless infection is severe. In keeping with our disease triangle, it is important to note that only expanding leaves are susceptible to infection. Regardless of our weather conditions in the next few weeks, maturing leaves will resist infection and this disease will have run its course…for this year. What will happen to this fungus then?

The spores of Taphrina are produced on the surface of diseased leaves by naked asci. It is important to find these signs to make an accurate diagnosis. They are washed or blown onto twigs and leaf buds, where they will overwinter. As leaves emerge next year, the spores come in contact with the young, expanding leaves. If the environmental conditions are cool and wet, the spores germinate and infect the leaf tissue.

If this disease becomes a problem several years in row, or in three of the last five years, homeowners may wish to plan ahead and apply a preventative fungicide just prior to budbreak next year. Several fungicides that are labeled for home use for control of Taphrina diseases and include: · Lime sulfur
· Chlorothalonil (Bravo, Daconil)
· Bordeaux mixture
· Fixed Copper (Kocide, Top Cop)

One final note: There are two other species of Taphrina, Taphrina caerulescens, the causal agent of leaf blister on oak species or Taphrina communis, the causal agent of plum pockets.

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

Friendly Flies
Jeff Hahn, Assistant Extension Entomologist

Flies on legs. Photo credit: Jeff Hahn

During the last week of June, people have been seeing medium-sized, 3/8th - 7/16th inch long flies in northern areas of Minnesota where forest tent caterpillars have been common. These flies have red eyes, a grayish body, three black stripes on their thorax, and a checkered abdomen. These flies are a type of flesh fly known to entomologists as Arachnidomyia (=Sarcophaga) aldrichi. They are important because they parasitize forest tent caterpillars and are a significant factor in ending outbreaks by these defoliators.

These flies emerge about mid-June and are active until about mid-July. During this time adult females deposit living young (maggots) on forest tent caterpillar pupae. The maggot bores into the pupa and feeds on the caterpillar inside, eventually killing it. When the maggot is done feeding, it drops to the ground to pupate where it remains until next June.

However, these flies become nuisances themselves, often occurring in tremendously large numbers. People describe seeing hundreds or even thousands of these flies at a time. These flies are very deliberate in their movements. They are not easily scared away and return quickly when brushed aside adding to the frustration of their presence. They land on just about anything including buildings, cars, laundry, even people! They seem to be particularly attracted to objects that are colored white.

Because these insects are so challenging to discourage, people commonly call them friendly flies. They are also occasionally referred to as government flies because of the mistaken belief that the were imported into the state to combat forest tent caterpillars. However, like forest tent caterpillars, friendly flies are native to North America.

Despite their nuisance, friendly flies do not bite and are otherwise harmless to people. They can cause problems on objects they are resting on by staining them with fecal droppings. Although people would dearly love to discourage these flies, there isn't any practical method to repel them or keep them away from people or property. The only thing that people can do is to tolerate them as best as possible until they go away on their own.

For a close up view of a friendly fly, go to:
http://www.nrcan.gc.ca/cfs/pub/digest/hardwood/arachn_e.html

Ichneumonid Wasps
Jeff Hahn, Assistant Extension Entomologist

Ichneumonid wasps. Photo credit: Jeff Hahn

People have noticed a type of large insect in the landscape over the last couple of weeks. Some have thought it was a dragonfly while others wondered if it was a mayfly. The insect in question is actually a type of ichneumonid (ich-new-MON-id) wasp known as Megarhyssa (meg-a-RISS-a). Megarhyssa is reddish brown and yellow insect with a body length of about one and half inches long. It possess an ovipositor attached to its abdomen that is another two inches long making the overall size nearly four inches. If you examine the ovipositor carefully, you will also notice it actually has two additional parts which are the two halves of the sheath.

Ichneumonid wasps are parasites of other insects. Megarhyssa is a parasite of horntails. Horntails attack dying or recently dead hardwoods, such as oak, maple, birch, and elm. With her long ovipositor, Megarhyssa can drill 1/2 inch or more into the wood to deliver an egg into the horntail larva. That egg hatches into a larva which attacks the horntail, eventually killing it. After it matures into an adult wasp, it emerges from the wood.

Despite her large size and her menacing ovipositor, ichneumonid wasps like Megarhyssa, pose no threat to people. They are not aggressive towards people and avoid us when possible. It potentially could jab you with her ovipositor in an effort to escape if it was in a threatened position but it would inflict only a minor wound at best. Some people that are allergic to bees are concerned about this insect. But their ovipositor does not possess venom like a stinger and is not dangerous to people that are sensitive to stings.

If you see a Megarhyssa, just ignore it. Any that are found on your property will go away on their own in a short time. There are no circumstances that justify treating them with an insecticide.

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

Bumper Crop of Bunnies
Beth Jarvis, Yard & Garden Line

Can you see the rabbit?
Photo credit: Don Breneman

Minnesota gardeners are hopping mad this year from seemingly higher level of bunny browse in their gardens. Rabbits have been spotted in urban yards in greater number and with, at least imagined, greater nonchalance than years previous.

In an attempt to locate a few plants that might be spared a rabbit onslaught, a group of Master Gardeners (MG) were polled though a list serve for their experience. The following is gleaned from over 40 responses. It is totally unscientific, purely anecdotal, but hopefully of some interest. There is a list at the end reporting some of the data.

Coping
Several Master Gardeners reported providing alternate food, such as corn or sunflower seeds seems to keep the rabbit feeding damage to a minimum. One Master Gardener noted the "cute as a button" baby rabbits were welcome to feed on the sprouts underneath his bird feeder only as long as they left the garden alone.

A Chippewa Co. MG successfully scares rabbits from her peas and beans by using the silvery hologram print pinwheels. In Carver Co., spun-bonded polyester floating row covers placed for a few weeks over tender transplants works well to protect plants.

Pepper spray as a deterrent was both endorsed and deemed useless. Repellent sprays, and dried blood must be reapplied after rain. (And it should also be noted that dried blood is 14% nitrogen. Applying it on the plants will cause fertilizer burns and it could prompt plants to produce foliage at the expense of flowers.) Mothballs were also mentioned. Naphthalene mothballs certainly shouldn't be used where children can reach them.

An Isanti MG raises catnip that she claims attracts cats which keep the rabbits away. Cats were generally considered to be effective at rabbit control. Several Hennepin Co. MGs cheered on some fox they'd seen in western Minneapolis. A Washington Co. MG has a resident hawk, owl and bald eagle and reports little trouble with rabbits.

Fencing generally gets the nod for most effective barricade method, though one MG reported finding baby bunnies in a leafy clump of perennials inside one of her fenced gardens.

The standard recommendation for garden fencing, according to a Michigan state publication, is: "Surround the garden with 36 inch widths of chicken wire attached to stakes. Bend the bottom 6 inches outward along the ground to prevent digging under the fence. By bending the top 6 inches outward, you can also prevent other animals from climbing the fence."
(The full text is at: http ://www.msue.msu.edu/msue/imp/modwl/11209808.html )

Several MGs reported clematis chewed off "at bunny level". Since clematis vines are left on the trellis over winter, some type of mesh protection could be worthwhile. Tress and shrubs also suffer from rabbit feeding during the winter. According to the Extension publication Protecting Trees and Shrubs Against Winter Damage:
"Trees can be protected from rodent damage by placing a cylinder of Ľ-inch mesh hardware cloth around the trunk. The cylinder should extend 2 to 3 inches below the ground line for mice and 18 to 24 inches above the anticipated snow line for rabbit protection. Hardware cloth can be left on year-round, but it must be larger than the trunk to allow for growth. For small trees, plastic tree guards are also effective. You can protect shrub beds from rabbits by fencing the beds with chicken wire; however, check such fenced areas frequently to ensure a rabbit has not gained entrance and is trapped inside."

Three Stars in Bunny Cuisine Magazine

'Stargazer' lily
--delicious!
Photo credit: Beth Jarvis

Time of year seems to play a major role in rabbit feeding pressure, with winter and spring seeing the most damage. It's understandable, when food supplies are low, the rabbits will eat pretty much anything. Expect bark damage on unprotected apple, pear, hawthorn, mountain ash. Flowering plum (Prunus triloba), smooth and staghorn sumac will be browsed as will roses, raspberries, blueberries and tender growth of pine, arborvitae and spruce. Cotoneaster, lilac suckers, viburnum and azalea may also be munched. Winged euonymus/burning bush is a winter treat many reported. However, burning bush is also a very popular winter food for meadow mice as well. Chris Goodwin, Bell Museum of Natural History, said you can tell the difference between rabbit nibbling and other creatures by looking at the chew marks. Rabbits have 4 front incisors, rodents have 2.

Goodwin also notes that rabbits will eat almost anything if there are no other choices. In years with lush vegetation, rabbits "have the luxury of being choosy." Even thorny roses are devoured. The cultivar most frequently cited as browsed to bits was ‘Bonica'.

Crocus may have a whisper of a chance in early spring, though snowdrops, which emerge before the crocus, go unscathed. Tulips are scarfed up while daffodils are rejected. Tender seedlings, especially peas and beans, are dearly beloved of rabbits, yet carrots, spinach and lettuce are ignored. Evergreen rhododendrons are generally shunned but the deciduous azalea, which is in the genus Rhododendron, is nibbled.

Yes, it does seem that some plants do seem to be avoided by rabbits. Astilbes, peonies, iris, fern, foxglove, seem to be pretty universally ignored. Ornamental/native grasses and many of the native plants now raised as garden plants also earn no stars in the gourmet garden guide.

Red salvia (Salvia splendens) was reported to be bunny ambrosia yet the blue salvia (Salvia farinacea) in the same yard was shunned according to one Master Gardener.

Another reported unintended side by side trials, where bunnies ate all the cucumber plants of a non-bitter cultivar and none of a standard cultivar.

Though, depending on what else is available, results can be mixed. Hostas were reported equally as fed upon or ignored, as were marigolds. Sedum, possibly the tall, were uneaten while the creeping sedum were deemed excellent for snacks. (Some MGs just said ‘sedum'.)

Lagarus ovatus
Photo credit: Univ. of Ill. Extension

Maybe rabbits have a sweet tooth? Rabbits are certainly love strawberries and blueberries, or at least the plants. In one garden, rabbits were reported standing up on hind legs to reach cherries from a dwarf tree!

Unlike deer, which might feed in a back yard but not the front, rabbits aren't shy. Foundation plantings seemed to fare no better than garden beds away from buildings. In fact, in Mahtomedi, rabbits have been jumping up onto a deck to get at plants in containers. And what has tempted them to risk venture so close to humans?? The taste treat of choice was Hare Grass or Bunny Tails (Lagarus ovatus).

Reported: Eaten	Reported: Not Eaten
Tulips	Iris
Crocus	Astilbes
Hostas-also not eaten	Daylilies (Hemerocallis spp.) (occasionally browsed)
Roses	Hosta
Clematis	Peonies
Dogwood	Sedums (creeping cvs. are browsed)
Garden lilies (Lilium spp. )	Alliums (rarely browsed)
Garden peas	Baby's breath (Gypsophilla spp.)
	Carnations/Dianthus
	Ferns>
	Wisteria

Editorial Notes

Flower garden at Mount Vernon,
Photo credit: Beth Jarvis

Next issue we'll be hearing from Nancy Rose who will talk about recent and potential woody plant introductions.

You've probably noticed this issue is short on articles for a summer issue. Deb Brown, one of the 3 primary authors, is out on medical leave for a bit. She's doing fine. Mending just takes time.

At left is a shot of a flower garden at George Washington's home at Mt. Vernon. Just a spot of color in a rather monochrome issue.

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

Previous Page

University of Minnesota Extension Service Home Page
In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota county extension office or, outside of Minnesota, contact the Distribution Center at (612) 625-8173.

The University of Minnesota Extension Service is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.