Yard & Garden Line News May 15, 2003

Yard & Garden Line News
Volume 5 Number 7 May 15, 2003

Features this issue:
Edible Plums for Minnesota Home Gardens
Ultra Low Maintenance Lawns
Avoiding Grape Disappointments
Garden Show Moves to Thursday
Editorial Notes

Edible Plums for Minnesota Home Gardens
Doug S. Foulk, Regional Extension Educator, Horticulture

'Alderman' in bloom. Photo credit: Doug Foulk

In early spring you may notice, in addition to the ubiquitous 'PJM' rhododendrons in bloom, a few yards sporting smallish trees with burgundy-tinged brown bark and lovely small white blossoms that cover the branches. It being too early in the season for the ornamental crabs to be in bloom, you may wonder what type of tree is brave or foolish enough to bloom when the weather is still so unpredictable. Chances are good that you are admiring plum trees.

Plums are a type of stone fruit. Stone fruits are characterized by a hard "pit" at the center and include peaches, almonds, cherries and apricots. In general, most stone fruit species, including peaches and sweet cherries, are very sensitive to winter injury and bloom earlier in spring than apples, making them unsuitable for growing on most sites in Minnesota. Fortunately there are a handful of ornamental as well as edible European (Prunus domestica) and hybrid (often complex crosses between P. americana, P. salicina, and other species) plums that perform acceptably in our climate, making them suitable for Minnesota home gardens and landscapes. Ornamental plums are attractive, but the edibility of the European and hybrid fruit is a real bonus for the home gardener.

How Many Trees?
The European plums we can grow in Minnesota are self-fruitful, so that only one tree is required. This is not the case for hybrid plums, however. Not only do hybrid plums require a second variety within about a hundred yards for pollination, they require an actual 'pollenizer variety.' Therefore, in order to get much fruit from a hybrid plum, you will want to plant one of the pollenizer types. 'Toka' is the most commonly available pollenizer in our area, but you may also find 'South Dakota' or 'Compass' for sale in some garden centers. 'Superior,' a hybrid variety, and the ornamental American plum Prunus americana seem to serve as acceptable pollenizers as well. Of course, if you are growing a hybrid plum for ornamental purposes only and do not desire fruit, or if your neighbors are growing a pollenizer plum variety, then a single plant is sufficient.

'Alderman' fruit. Photo credit: U of M Extension Svc.

The Varieties
Plum varieties exist for all parts of Minnesota, north and south. When you visit your local garden center, here are some of the varieties you may find (an M before the name indicates a University of Minnesota release, and ripening times are for the Horticulture Research Center in Chanhassen).

M Alderman: Introduced in 1986, this variety is a perfect combination of ornamental and culinary qualities. The tree itself has a wonderful horizontal branching habit that really adds drama to the landscape, while the burgundy-skinned fruit is large with soft, sweet golden flesh. The fruit ripens in late August. 'Alderman' is hardy throughout the southern half of the state.

M LaCrescent: This variety from 1923 is only moderately productive, but the small, yellow-skinned fruit has a flavor suggestive of apricots, making it an excellent addition to the home garden. 'LaCrescent' is one of our hardiest varieties as well and is suitable for growing throughout Minnesota. Fruit ripens in early August.

¤Mount Royal: The hardiest tested European plum for Minnesota, 'Mount Royal' is nonetheless only recommended for the Twin Cities and south. The smallish, blue-black-skinned fruit is of good fresh eating quality.

¤Pembina: From South Dakota, this hybrid plum produces large pointed fruit with red skin and yellow flesh of good quality. Ripens in late August and should be hardy into parts of USDA Zone 3.

M Pipestone: Released in 1942, 'Pipestone' produces large fruit that is easily peeled for those who object to its tough red skin. Especially well-suited for jams and jellies, 'Pipestone' ripens in late August and, like Pembina, should be hardy into parts of USDA Zone 3.

¤Stanley: A European plum, 'Stanley' is not as hardy as 'Mount Royal,' but produces a large annual crop of high quality blue-skinned fruit without the presence of a pollenizer. 'Stanley' will be most successful to gardeners in far Southeastern Minnesota and should otherwise only be attempted on protected sites in the southern third of the state.

M Superior: One of the best choices for the southern third of Minnesota, 'Superior' produces very large red-skinned fruit in mid-August. The fruit is juicy and sweet for fresh eating and makes excellent jams and jellies. The trees have a somewhat weeping growth habit and bear heavy crops-hand-thinning fruitlets in spring will result in larger fruit at harvest. Although 'Superior' can be used as a pollenizer for most hybrid plums with fair-to-good results, it will not pollinate 'LaCrescent.' Released in 1933.

Toka in bloom. Photo credit: Doug Fouk

¤Toka: From South Dakota, 'Toka' is the best of the pollenizers, but is also an excellent tree in its own right. The fruit, although small, has a rich, aromatic flavor that is unique among available hybrid plums. 'Toka' ripens in mid-August and is hardy in the southern half of the state.

M Underwood: One of the hardiest of the hybrid plums, 'Underwood' has been pleasing home gardeners since 1920, making it also the oldest of the commonly available U of M releases. The fruit is medium-sized and of good eating and jam-making quality. 'Underwood' is an especially early hybrid plum, producing ripe fruit beginning in late July.

¤Waneta: From South Dakota, 'Waneta' is another early ripener, producing fruit from late July into early August. Hardy into USDA Zone 3, the reddish fruit with yellow flesh is of good eating quality.

You may encounter other varieties at garden centers and through mail-order nurseries, and some of them may prove to be reliably hardy in Minnesota. However, because they have not been tested by the University of Minnesota, grow such varieties on a trial basis only.

Planting, Training, Care and Pests Once you have chosen and purchased your plum trees, you will want to take proper care of them, from planting to harvest. For more information on these topics, read the University of Minnesota Extension Service publication "Growing Stone Fruits in Minnesota Home Gardens" (FO-1125-C). You'll find it at http://www.extension.umn.edu/distribution/horticulture/DG1125.html.

Doug picking plums. Photo credit: Michael Ponto

And although plums are easier to grow than apples, pest problems do occasionally crop up. The list of problems to look out for includes:

Black knot is a fungal disease that can cause galls reminiscent of burnt marshmallows on a stick. For more information on this disease, a Yard and Garden Line Brief by that name is available at http://www.extension.umn.edu/yardandgarden/ygbriefs/p417blackknot.html.

Brown rot overwinters in infected fruit and can often be controlled using simple sanitation methods. For a description and photo of brown rot, navigate to http://www.extension.umn.edu/projects/yardandgarden/diagnostics/cherrybrownrot.html.

'Plum pockets' is a fungal disease producing dramatic symptoms, but rarely affects a large portion of a crop. The Yard and Garden Line Brief at http://www.extension.umn.edu/yardandgarden/ygbriefs/p243plumpockets.html provides more information.

Plum curculio is a native insect pest with many hosts, including apples, cherries and plums. Curculios damage plum fruits when they feed on the flesh or lay eggs under the skin. For more information on this potentially destructive pest, consult the Ohio State University Extension Fact Sheet "Plum Curculio and Its Control" (HYG-2043-88) at http://ohioline.osu.edu/hyg-fact/2000/2043.html.

Finally, the peachtree borer is a serious pest of stone fruits in many parts of the country and may significantly shorten the life of plum trees. For a description of this pest, the Ohio State University Extension Fact Sheet "Peachtree Borer" (HYG-2032-94) is an excellent source of information. You'll find it at: http://ohioline.osu.edu/hyg-fact/2000/2032.html.

Plum trees in Minnesota have a lot to offer. Their smaller size fits well into most landscapes, and their early bloom provides beauty when most plants are only beginning to grow. Finally, their fruit is delicious and unlike anything you can buy at the grocery store, providing a juicy bit of late summer goodness before the fall apples arrive.

Ultra Low Maintenance Lawns
Deborah Brown, Extension Horticulturist

Ecology Mix, not mowed.
Photo credit: Mary Meyer

Every year we get calls from people who want to greatly reduce the amount of maintenance they put into their lawns. Many would prefer to eliminate lawns altogether – but that would leave them no area to walk on, or let their children or pets play on. The following is an article I wrote for the Star Tribune two years ago discussing some very low-maintenance lawns. It seems like a good time to re-visit the subject.

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Despite knowledge that lawns contribute in many positive ways to our environment, there are compelling reasons a person might want to explore alternatives to the typical Minnesota bluegrass lawn. First is probably a desire to reduce time and effort spent on maintenance activities such as frequent mowing, watering, fertilizing, and weed control. This becomes especially important when the terrain doesn't lend itself particularly well to lawn care, or when the lawn is really large.

Often people's hectic lifestyles barely allow them to eke out enough time for leisure activities. While some find lawn care pleasurable and relaxing, others find it an imposition. They don't want to feel like slaves to their lawns, nor do they like the pressure of having to "measure up" to neighborhood standards. And, yes, some people simply prefer the aesthetic values of a more casual, less precisely manicured yard.

Until recently, the most obvious approach has been limiting the size of the "formal" lawn portion of a yard, at the same time increasing space devoted other elements in the landscape. These include trees, flower gardens, and shrub beds as well as components of the hardscape: decks, walks, rocks, and patios.

Some people with sunny, exposed sites have installed prairie plantings to replace their lawns, or large portions of them. Generally, the more rural the property and the more obviously planned and purposeful the prairie planting, the better it's accepted. In urban and suburban areas "prairie lawns" often meet with mixed reactions. People may find themselves bumping up against local governmental restrictions, and in some cases, disapproval by neighbors who fail to see the beauty of prairie plantings, choosing instead to view those yards as merely unkempt.

(Fortunately, there's a growing movement towards more prairie gardening, and people's attitudes are changing. As long as a yard looks maintained – perhaps with a nice fence or bird houses – and care is taken to prevent large weed infestations, people are becoming more accepting of prairie plantings in front of houses, not just in back.)

A "different" lawn

Yarrow in Ecology Mix, not mowed.
Photo credit: Mary Meyer

Now there's another option to consider. Keep your lawn, but replace all existing grasses with one of the new extremely low maintenance grass mixes. Once established, they should substantially reduce – though not eliminate – routine lawn maintenance.... and you'll still have a green lawn to walk on and enjoy.

Several of these low maintenance lawn mixes have been planted, then monitored for three years in research plots at the Minnesota Landscape Arboretum and at the Waseca branch of the University's Agricultural Experiment Station. While no one would mistake the results for a highly maintained golf course or finely manicured lawn, some were considered "acceptable" by the crew of Extension personnel and Master Gardeners who evaluated them monthly throughout each growing season.

All these lawn mixes grow best in full sunlight or very light shade. They are not suited to dense shade or to poorly-drained, heavy clay soils. Among the best choices were blends of different fescues (grasses grown for their shade and drought tolerance) and seed mixes containing a combination of grasses and some small broad-leaf or flowering plants such as clover. If you think of clover as a weed, stick with the fescue blends. If you can accept the concept of a lawn as a "community" of different plants, you might enjoy the mixes that include clover and other small flowers.

Plant in fall
Eliminate all weeds prior to planting. This may take from several weeks to several months, depending on how you go about it. If you want to avoid using herbicides, rent a sod cutter and scrape the upper two to three inches of grass and soil shortly before planting. The seed bed must be smooth and free of clumps, as well as weed-free. Have your soil tested for an exact nutrient recommendation, or simply incorporate one pound of 10-10-10 fertilizer per thousand square feet you'll be seeding. (It is legal to use a fertilizer with phosphorus to establish new lawns.)

Though technically you could plant these mixes in spring or fall, your job will be easier and your results, better, if you plant between mid-August and mid-September. In spring, any weed seeds that are churned up in the planting process will compete with desired seeds for moisture and nutrients, whereas in fall, most weed seeds won't sprout. By the following spring your low maintenance lawn will have had such a good head start it will prevent most weed seeds from getting a toe-hold.

Routine maintenance
Water daily while seedlings are developing, but once the lawn becomes established you'll only need to water occasionally, during prolonged periods of hot, dry weather. Fertilize sparingly, if at all. When necessary, use a slow-release fertilizer sparingly in early spring. Typical high nitrogen lawn fertilizers encourage top growth – not what you want when you're trying to avoid mowing.

Mowing frequency depends on how you'd like the lawn to look. You'll probably want to mow it to four inches when seed heads develop towards the end of spring. Then you can mow monthly – again, to four inches – or simply leave it alone. It should not grow taller than about six inches, and depending on which mix you use, the grasses will often bend gracefully, presenting a relatively low profile.

It's important that you rake the leaves off your low maintenance lawn each fall. If there aren't huge piles of leaves, you can just run over them with a mulching mower so that tiny leaf chips filter down and recycle some nutrients to the soil.

If all this seems too radical to try throughout your yard, why not plant just part of it next fall, then make your own observations? You might well be convinced it's worth the initial effort, considering all the time you'll save later.

Here are some possible seed sources for ultra-low maintenance lawns:

No Mow Lawn Mix (six difference fescues)	Prairie Nursery P.O.Box 306 Westfield, WI 53964 www.prairienursery.com http://www.prairienursery.com/catalog/cat_nomow.asp
Dryland Ecology Lawn Mix (perennial ryegrass and fine fescue with some flowers and clover)	Nichols Garden Nursery 1190 North Pacific Highway Albany, OR 97321-4580 http://www.nicholsgardennursery.com
Fleur de Lawn (mostly perennial ryegrass with some flowers and clover) < /td>	Hobbs and Hopkins, Ltd. 1712 SE Ankeny Portland, OR 97214 http://www.protimelawnseed.com/fleur_de_lawn.htm

For more information on the alternative turf trials conducted by Mary Meyer, Extension Horticulturist, please see: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-Dec0100.html#turf

Avoiding Grape Disappointments
Janna Beckerman, Extension Plant Pathologist

Foliar anthracnose on grape. Photo credit:
Sandee Gould
Plant Disease Clinic

Every spring, grape growers across Minnesota anxiously anticipate their fall grape harvest. The fungus Elsinoe ampelina, causal agent of grape anthracnose or bird's eye rot, is also eagerly anticipating the emergence of succulent new growth, but for different "reasons." Now is the time to begin your management strategy if you wish to harvest grapes in the fall!

Symptoms and Signs:
The symptoms of anthracnose on fruit, stems and leaves should not be confused with black rot, other diseases, or hail. Infections begin with yellowish areas on the leaves that eventually develop into discrete gray lesions with a dark border. The areas of fungal infection start quite small and spread in size rapidly under wet, humid conditions. Severely infected leaves may become distorted and curl down from the margins. Lesions may coalesce, resulting in shoot death.

As the disease progresses, stem lesions develop that are similar in color to leaf leasions, however, these lesions are sunken, but with slightly raised borders. Infected areas may crack, causing shoots to become brittle. Anthracnose lesions on shoots may be confused with hail injury. It is important to note the location of the lesions. Hail damage uniformly impacts one side of the branch, whereas anthracnose will have a random distribution. When examining the wounds, be sure to note lesion margin: Raised black margins are indicative of anthracnose, as opposed to discrete non-spreading lesions if hail caused the damage.

Fruit anthracnose on grapes. Photo credit: Peter Hemstad
H.R.C.

Grape clusters are susceptible to anthracnose infection before flowering through véraison (no, not the cell phone company, but the "the period in ripening where berry growth ceases and coloration (of red varieties) commences.") Rachis and pedicel lesions are similar in appearance to shoot lesions, but on a smaller scale. If the rachis becomes girdled, the cluster may shrivel. Fruit infections have light-gray centers and reddish-brown borders. Cracking may result due to infection, however, infected fruit often remains firm and resembles a "bird's eye" . It is interesting to note that the leaves surrounding the infected grapes may turn brown, wilt, curl or drop off.

Elsinoe ampelina, the fungus that causes grape anthracnose, produces acervuli, fungal cushions, within the symptomatic lesions. If looking at the acervuli under the microscope, characteristic ovoid spores, with one to two "dots" may be observed. By autumn, the fungus begins the production of sclerotia, thick "fungus balls" that enable the organism to persist in severe weather. In the spring, the sclerotia are capable of releasing conidia to begin the infection cycle anew. The fungus is also capable of a sexual (perfect) state that can also infect in the spring.

Who's at risk?
Although numerous grape varieties are susceptible to anthracnose, most cannot be successfully grown in Minnesota. Although some vinifera and vinifera- hybrids seem to be uniquely susceptible, recent introductions of vinifera- hybrid grapes, like Frontenac and Swenson's White have been found to have good resistance to this disease. Anthracnose is mainly a problem in poorly maintained vineyards that are already at risk due to heavy soils, poor air circulation, and lack of sanitation. Once infection becomes established, developing spring rains splash water and quickly spreads the fungus to both healthy, new succulent growth, and even previously healthy vines. If this disease is not properly managed, recurring anthracnose outbreaks (over a period of two or three years) can weakens vines, and predispose them to other infections and damage.

Managing Anthracnose
Sanitation is very important to managing this disease. Severe annual pruning is an essential practice for controlling anthracnose because the pathogen overwinters in old canes. Prune out infected canes and select only strong, healthy canes from the previous year's growth. The selected canes should be as free of disease spots as possible-When in doubt, prune it out! Not only are you reducing inoculum, you are increasing air flow throughout the canopy, which results in drier leaves and less disease. After fruiting canes have been removed, continue and remove excess growth, mummy berries, leaves and any other obvious site that the fungus can overwinter. Quite simply, the amount of diseased material remaining after pruning is proportional to the level of disease next year. Keep in mind that any remaining inoculum compromises the effectiveness of your management program.

Fungicides for Home Use
Lime sulfur and copper containing fungicides are both effective in controlling the spread of the disease if applied when you first notice symptoms of damage. Apply liquid lime sulfur at bud break (when you see green tissue emerging from the leaf buds, 1/4 to 1/2 inch green). This organic fungicide is one of the most effective tools in preventing disease establishment. It should be noted that you may need to repeat applications of the fungicide multiple times over the course of the growing season because these fungicides have only a 7 day persistence. Failure to adhere to a controlled spray program will result in plants that may become re-infected when weather conditions become conducive to disease development.

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

Editorial Notes

'Alderman' fruit. Photo credit: U of Mn. Extension Svc.

We bumped Doug's plum article up to mid-May because we know you're shopping for plants now. I teased Doug that he had me thinking about making plum jam (and I have yet to plant the tree.) I had 'Alderman' plums once and *oh* they were wonderful!! Bred for flavor rather than resilency during shipping, they also had to be eaten quickly,so what I had left, I made into jam. In the June 1 issue, we'll hear about the display garden on the St. Paul campus.

If you're looking for insect articles, Jeff Hahn's been out sick for a week. He should be back up and writing by the June 1 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

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