Yard & Garden Line News August 1, 2003

Yard & Garden Line News
Volume 5 Number 12 August 1, 2003

Features this issue:
Who's Digging Holes in My Yard?
Late Summer; a Busy Time in the Perennial Garden
Out of the Frying Pan and into the Fire Blight
Viburnum Borers
August Garden Checklist
Editorial Notes

Who's Digging Holes in My Yard?
Bob Bystrom, DNR, retired, Washington Co. Master Gardener

Raccoon, a nocturnal visitor. Photo credit NPS Photo

Sometimes it's difficult to identify burrowing animals that have been damaging yards or gardens. They may be nocturnal or so elusive that we never see them. Nevertheless, identifying the animal is an essential step toward controlling or managing the damage.

Often the presence of a burrow or other signs of digging are the only available clue to the animal's identity. And the burrows themselves may be the damage, creating unsightly mounds or depressions that interfere with lawn maintenance and disturb or uproot valuable plants.

Here is a list of diggers and characteristics of their work that can be used to help identify the mystery animal. Please note that some animals that dig do not eat plants. For instance, moles eat soil insects and the plant and root damage caused by their digging is usually incidental.

Evidence	Animal
Mounds of soil that cover burrows so that no entrance is usually visible:
Conical mound	eastern mole
Rounded mound, often heart shaped	pocket gopher
Multiple tunnels near the surface that raise sod or soil. Tunnel entrance usually not visible:
In wet or swampy areas	star-nosed mole
In upland areas	eastern mole
Burrows (usually shallow) with no soil piled near the inconspicuous entrance:
Entrance about 2 inches, near stone walls, rock gardens or foundations, in brush, open woods or gardens	eastern chipmunk
Entrance 2 inches or less, in open areas with short grass	thirteen-lined ground squirrel
Entrance 1 to 1.5 inches, in open areas with heavy vegetation	meadow vole
Entrance about 1 inch, in open areas or woodlands, tunnel just under duff or deeper
shrew
(Some shrew species may appropriate vole burrows and runs and several may occupy one burrow system. Shrews usually do not damage plants.)
Entrance 2 to 3 inches, near or under buildings, wood piles, shrubbery or rubbish and near a dependable water source (stream, sewer, toilet, etc.)	Norway rat
(Several rats may occupy one burrow system )
Entrance 4 inches, near lake, stream or wetland	muskrat
Deep burrows with excavated soil spread around the entrance:
Entrance 10 to 12 inches, in fields, woodlands, under decks, or building foundations	woodchuck
Entrance 12 inches, in fields, grasslands, prairies	badger
(Badgers are scarce in Minnesota's seven metro counties, but a few may be found in the suburban fringe and developing areas).
Shallow excavations or "divots:"
In turf or mulch	skunk, raccoon, squirrel.
(This is usually a result of a search for soil insects or, in the case of squirrels, caching or retrieving food, such as corn, acorns or nuts.)
Surface runways in grass or tunnels in snow
Strewn with clipped grass or other vegetation in grass or snow	meadow vole
Under snow without grass	red squirrel
Potted plants dug up and/or pulled out
Damage occurs at night	raccoon
Damage occurs during the day	squirrel or woodchuck

Late Summer; a Busy Time in the Perennial Garden
Deborah Brown, Extension Horticulturist

Shasta daisies. Photo credit: Deb Brown

It's August, and you thought it was time to sit back, relax, and enjoy your garden. Yes.... and no. It's true; Minnesota flower gardens have been glorious this year. What could be more pleasant than pulling up a comfy lawn chair, pouring yourself a tall glass of iced tea and basking in the beauty you've helped to create.

But rarely are people perfectly contented with their gardens. Most of us consider each garden to be a work in progress. Usually by summer's end we already have ideas we're itching to implement the following year – new plants we've read about and would like to try, or spectacular plant combinations we've seen on garden tours or in our friends' yards. We might even give in to the temptation to extend the boundaries of our gardens to accommodate more blooms. (Who wants to mow all that lawn, anyway?)

Late summer (through early fall) is also time for "taking care of business" in perennial gardens. Even though perennials are often planted with the idea that they're easier to care for than flowering annuals, no plants are truly maintenance-free. By mid- to late August, depending on how far north you live, it will be time to dig up and divide perennials that have grown too large or spread too wide, encroaching on neighboring plants – or even obliterating them.

It's time for lifting iris to cut away the oldest, woody part of their rhizomes. It's also time to move plants that are growing in the wrong place based on size, flower color, or bloom time. And it's an excellent time to visit your favorite garden center to buy new perennials to add to your collection or to trade plants with friend who are dividing their perennials, too.

Whether you divide and replant existing perennials or shop for new ones, prepare the soil as you would for spring planting, incorporating plenty of organic matter along with some slow-release fertilizer. Water the plants well, then spread a couple inches of mulching material around them. Whatever you're using in the rest of the garden should be fine; woodchips, shredded bark or cornstalks, cocoa bean hulls, chipped leaves, pine straw, straw, or dried grass clippings are all commonly used where they don't need to be turned into the soil at the end of the season.

Because we often run into hot, dry weather this time of year, it's up to you to provide a regular supply of moisture for these newly divided and planted perennials. Water less frequently as temperatures grow cooler or if rainfall is ample. Then, when the soil begins to freeze – usually some time in November – cover the plants with additional mulch. Four to six inches of straw or marsh hay is ideal. If you use leaves, rake ten or twelve inches over the plants. Leaves tend to pack down, so they don't insulate as effectively as straw or hay with hollow stems.

With any luck we'll have better snow cover this coming winter, and all our plants will survive to bloom and thrive another year.

Out of the Frying Pan and into the Fire Blight
Janna Beckerman, Extension Plant Pathologist

Fire blight bacteria ovewinter in cankers. Photo credit Chad Behrendt

Although apple scab has been epidemic this year, a far more deadly disease of crabapples, and other members of the Rosaceae (rose family), has been on the upswing as well. Fire blight, caused by the bacterium Erwinia amylovora, affects over 130 plant members of the rose family, from tiny Grecian rose (Geum avens), to mighty apple trees. A comprehensive list of susceptible plants can be found at: http://www.aces.edu/pubs/anr/anr-542/anr-542.html.

In Minnesota, fire blight is most often seen on apple, crabapple, pear, mountain-ash, and cotoneaster. Unlike apple scab, the prognosis for infected trees, if not caught early, is grim.

Symptoms and Signs
Unfortunately, most people do not see the symptoms until the infection has spread. These symptoms include flagging branches and dieback. Careful examination may reveal a sunken canker. However, in most case, infection began with the flowers, which are the most susceptible organs on the tree. Infected flowers appear water-soaked, before shriveling, and turn into an oozy brown mass. As the infection progresses, leaves begin to turn reddish brown on most hosts, or black if the infected host is a pear. On pear, it appears as though the tree was scorched by fire, hence the name fire blight. The leaves hang downward and remain attached to blighted shoots, twigs and branches. Infected shoots eventually turn brown or black, and bend to form the diagnostic "shepherd's-crook" (Fig. 3). If infected fruit is present, it will quickly discolor. At this point, bacterial ooze may be seen after periods of wet weather. Eventually, the fruit mummifies, and may cling to the infected tree for months.

Flagging is a key symptom of fire blight affected plants. Photo credit Plant Disease Clinic

Unlike the zoopathogenic (animal-infecting) counterparts, phytopathogenic (plant infecting) bacteria do NOT produce spores to overwinter. Bacteria survive the winter within cankers, and become active in the spring and summer during warm, humid weather. Bacterial ooze, a combination of bacteria and plant sap, flows out of infected trees through natural openings like lenticels from bark and fruit. Bacterial ooze is spread to easily infected, young, succulent growth on nearby plants by wind, rain, insects and/or birds. Pollinating insects, attracted to the sweet smelling bacterial ooze, are the primary vectors of this disease.

Like all diseases, the interaction of host, pathogen and environment must come together for disease to occur. Severe hailstorms over the last two years, coupled with severe hail last month, have created numerous wounds that the bacteria can infect. The severity of these hailstorms was such that even resistant trees, like Haralson, were found to have fire blight infections last year as well as this year. The use of resistant cultivars is still the best method of managing this disease, although even resistant cultivars can become infected.

Management
There are several cultural practices that you can implement to reduce the risk and minimize the severity of fire blight. The first is choosing resistant cultivars. Although not immune to this disease, when properly maintained, resistant varieties do not generally become as severely infected as their susceptible counterparts. A list of Minnesota hardy, fire blight resistant apples and crabapples can be found at:
http://www.extension.umn.edu/projects/yardandgarden/ygbriefs/p223fireblight.html
The following woody ornamentals are considered resistant to fire blight:

Hawthorn: Crataegus arnoldiana, C. coccinea, C. crus-galli, C. douglasii, C. phaenopyrum, C. prunifolia, C. puntata 'Ohio Pioneer', C. viridis 'Winter King.'

Mountain-ash: Sorbus aucuparia, S. decora, S. hybrida and S. intermedia.

Shepherd's crook is a diagnostic symptom of fire blight.
Photo credit: Chad Behrendt

Properly pruning the trees in late winter before bud break reduces the risk of infection (Fall pruning of fruit trees is not recommended). Try to avoid heavy pruning, as that can stimulate excessive new growth. Never perform pruning for plant health and aesthetics with pruning to manage the disease-its too easy to infect or reinfect a tree. Care should be taken before fertilizing any fruit tree. Young, succulent growth is very susceptible to fire blight, and excessive fertilization has been linked to increased incidence of this disease. When fertilizing trees in early spring, use a balanced fertilizer to encourage tree growth when the risk of fire blight is low. Fertilizer applied to the lawn is usually adequate for the needs of nearby trees. Trees with dark green, well-developed leaves and adequate, but not excessive growth would not benefit significantly from an application of fertilizer. Furthermore, excessive nitrogen fertilizer will reduce a resistant plant's resistance to this and other diseases. To further reduce stress, plant new trees in full sun to minimize stress.

Although summer pruning can be hazardous to your tree's health, susceptible trees that are infected may be killed if the disease is not pruned out as soon as possible to prevent further spread. Infected twigs and branches should be cut at least twelve inches below the point of visible infection. As always, plan your cut at the appropriate pruning site.

If fire blight is seriously damaging a cotoneaster hedge, cut the hedge about six inches above the ground in late winter. If only a few stems are blighted, they can be removed as described for trees. Pruning shears should be sterilized between cuts {dipped for five seconds in a freshly made 10% bleach solution (one part bleach to nine parts water, equivalent to 1½ cups bleach in 1 gallon of water)}. Diseased twigs, branches, and trees may be removed in late winter. Cuts should be made at least six inches below the diseased area into healthy wood and at a proper pruning site.

If trees are severely infected or if fire blight continues to be a yearly problem, a copper-based fungicide like Bordeaux can be applied. Due to the development of antibiotic resistance, pesticides containing the active ingredient streptomycin sulfate are no longer recommended. Follow directions on the label for application procedures. Read the label carefully and apply only as directed.

Due to the persistence of the bacteria, replanting infested areas with susceptible trees is strongly discouraged. It must be stressed that if the inoculum levels are extremely high, even resistant cultivars can become infected, and replanting with them should be cautioned against as well.

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

Viburnum Borers
Jeff Hahn, Assistant Extension Entomologist

Adult borer.

Borer damage. Photos: Jeff Hahn

There are two species of clearwinged borers that attack viburnum, the viburnum borer, Synanthedon viburni, and the lesser viburnum borer, S. fatifera. Both species look virtually identical to each other and have very similar biologies. They have 1/2 inch long bluish black bodies with yellow markings and a 3/4 inch long wingspan. They have few scales on their wings so they appear clear. Clearwinged borers are day time flying moths. They are wasp-like in general appearance and as they fly.

These borers emerge as adult moths in late June and early July. They lay eggs at the base of American highbush cranberry (Viburnum trilobum), nannyberry (Viburnum lentago), and other viburnum species (no more than 18 inches from the ground). The larvae bore into the bark and cambium. They remain in the shrub the rest of the summer and through the winter before pupating the following spring. You might see pupal cases sticking out of the bark during spring as the caterpillars chew exit holes before they pupate.

Healthy viburnum may be attacked, but they are more likely to infest stressed or unhealthy shrubs or shrubs with wounds or cracks in the bark. Sites that are attacked result in twisted and scarred stems. As shrubs try to heal over old infestations, branches become swollen and distorted. Infested plants may wilt and have branch dieback. Heavily infested shrubs can be killed by these borers.

Protect your viburnum from borers by making them less attractive to insects. Plant them in proper sites. Keep them healthy through proper watering, mulching, and fertilizing. Avoid any wounding, e.g. with weed whips and lawn mowers.

You can protect your shrubs with an insecticide application. Products containing permethrin are effective. The timing of the insecticide is critical for the treatment to be successful. You want to target your spray in late June or early July when adults are active. Treat the shrub's stem from the soil to 18 inches above the ground.

If you are not sure when adults are active, you can improve your timing by using a pheromone trap. These traps use a chemical lure that are attractive to males. When you start to capture moths, you know they are active. Make your insecticide application about 10 - 14 days after you capture the first moth. You can purchase pheromone traps for clearwinged borers from different IPM-oriented retail companies, such as Great Lakes IPM, Trece, and Pherotech.

Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/EntWeb/Ent.htm
August Garden To-Do List
Beth Jarvis, Yard & Garden Line

Daylilies may be divided now. Photo credit: Beth Jarvis

This list is not all inclusive, but it's a start. Compiled from conversations with: Bob Mugaas, Doug Foulk and Patrick Weicherding Metro area Extension educators.

Flowers:
*See Deb's tips in her article.

*Cut back faded bleeding heart foliage. It normally dies back in late July-early August.

*Do not fertilize garden roses after August 1. For more info, see Culture of Garden Roses.

*Daylilies may be divided after they've finished blooming. Additional facts and tips on daylilies can be found in: Growing Daylilies

Lawns:
T'is the season for lawn renovation!

*Lawn renovations such as reseeding, dethatching/power raking, core areating can be started in August. For a list of when to do what, go to: http://www.sustland.umn.edu/maint/index.html
click on lawn maintenance, scroll down to: Upper Midwest Home Lawn Care Calendar for Cool Season Grasses.

*If you're fertilizing your lawn in the fall, make your first application between mid August and mid-September.

It's too late to try treating mature crabgrass plants. You'll get more effective control using a pre-emergence product in the spring.

Apply some water during extended dry periods. On lower maintenance lawns, rather than an inch a week, you can cut back to a half inch every weeks.

Trees & Shrubs
*Hold off on fertilizing trees and shrubs until they go dormant. A low nitrogen, slow release (eg: organic ) fertilizer is ok but a high nitrogen application may prompt additional growth and prevent the plants from beginning to go dormant. Fall lawn fertilizer applications aren't a concern as the grass captures most of the nitrogen.

*It's too early for fall pruning. Save this task for Oct.-Nov

*Makes sure tress and shrubs get an inch of water a week from now until the ground freezes. Drought stress will prevent hardening off for winter.

Fruit
*Pick up windfall fruit as as this fruit is often infested with insect larvae. You want to keep the larvae from moving to the soil and overwintering there.

*Don't put windfalls in the compost pile. Dispose of them in accordance with local ordinances.

*If you haven't done it yet, now's the time to prune out any raspberry canes that produced fruit this summer. They are 2 year old canes that will not produce further and will die.

*Decrease widths of rows of summer bearing raspberries to 12 inches wide.

*Prune root suckers from apples now as trees are less likely to initiate new suckers.

*Harvest plums and early apples. *For a most comprehensive guide to selecting and growing apples and pears, see Growing Apples and Pears in Minnesota Home Gardens, a web-ony Extension pub at: http://www.extension.umn.edu/distribution/horticulture/applepear.html

Editorial Notes

Rock garden, Bellevue, Wa. Photo credit: Beth Jarvis

The second part of "The Considerate Gardener's Guide to Pesticides" has been delayed until Sept. 1 due to circumstances beyond our control. We regret any inconvenience.

I took the photo at left in July '02 in the Bellevue Botanical Garden, Bellevue, Washington. It is a lovely spot and worth the stop if you're in the Seattle area. The webiste is: http://www.bellevuebotanical.org/

Still on the list for upcoming issues: Dr. Tim Kurtti, who does deer tick research. In a bit, we'll hear about the closest thing we have to Japanesese maple. Dave Hanson, who works w/Gary Johnson in Urban Forestry, has agreed to pen a piece dispelling myths about tree roots, be they heaving sidewalks, invading basement walls or sewer pipe, or whatever.

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 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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