Yard & Garden Line News
Volume 8 Number 9                                                               June 15, 2006
Features this issue:

In Search of: New Fruits
Minnesota Blues
Little Green Weevils
Blister Beetles
Masked Hunters
Seeing Spots on Local Maples
Garden Calendar
Editorial Notes

In Search of: New Fruits
Beth Jarvis, Yard & Garden Line

'Itasca' strawberry Photo credit:
Dave Hansen
Recently I had the privilege to visit with David Bedford, a fruit breeder, at the University of Minnesota's Horticulture Research Center, Excelsior. We sat in his office in the converted farmhouse on the property. Snoozing in another chair was the Center's latest in rodent control-a calico cat named Tina, after Tina Turner. Mice eat seedlings growing on greenhouse benches as well as seeds. Problems with mice have decreased since Tina's arrival.

Bedford has wide-ranging interests and our conversation skipped from fruit to fruit. Apples are his passion and will be discussed in part 2.

It's perhaps a common misconception that the U's plant breeding programs release multiple new plants every year. In fact, there have been 102 fruit releases since the program started almost 100 years ago. Plant breeding can be a time consuming, laborious process.

The current fruit breeding program has been scaled back to enable the staff to focus on areas of particular interest. The main breeding efforts presently center around: apples, grapes and blueberries. The small fruit breeding program, which includes raspberries and strawberries is being deemphasized but could easily be reactivated at a latter time if funding permitted. Breeding projects such as apples which can take up to 30 years to develop a new cultivar are more difficult to stop and restart.

Strawberries:
The strawberry program is no longer making new crosses but is continuing the evaluate advanced selections from previous crosses. The current pool of 35 selections represents 2-5% of the original breeding population.

Strawberries undergo field trials in Morris, Grand Rapids and Victoria locations with distinctly different soils and growing conditions. When all the data's collected and evaluated, the fruit breeders will decide if any deserve introduction. Because of our highly variable weather, it can take 10 years of data to generate a decision. Evaluations compare crosses for productivity, fruit quality and disease resistance, against standard, available cultivars. If a selection doesn't represent an improvement, it's not worth releasing.

Response to climate can play a role in a berry's release. During trials of two recent releases, 'Winona' and 'Mesabi', 'Mesabi' grew very well in Grand Rapids but was less remarkable in zone 4. 'Winona', on the other hand, was a standout in southern Minnesota.

'Itasca' is the latest release and should be generally available soon. Two more selections in trials should be released in the next 3 to 4 years.

Strawberries that grow well on the east coast may often grow here. The west coast producers raise completely different cultivars. While California strawberries are often massive, Bedford feels the Minnesota- grown strawberry wins on flavor. There's a healthy, small strawberry industry in Minnesota.

When asked why strawberry beds aren't awash in seedlings sprouting from spoiled berries, Bedford paused a moment, then pointed out that strawberry seeds are small, hard to handle, and difficult to germinate plus the seedlings are really tiny and fragile. Strawberries reproduce far more reliably through clonal reproduction, the daughter plants, than sexually, through seeds. Bedford surmised that seed propagation is a secondary form of propagation for the fruit, one that will ensure dispersal by birds and other critters.

Blueberries:
Blueberries grow very well in trials in Becker and Grand Rapids where the soil is ideal for them. Crosses are not currently being made though several new cultivars will be introduced from material that is entering final stages of testing.

To be commercially viable, crosses must be easy to propagate. Minnesota releases are called half-highs because they're crosses between the high bush blueberries of the east and the native low bush. While high bush are easily propagated from stem cuttings, low bush aren't and some half-highs inherit that trait. Half-highs are usually commercially propagated in tissue culture.

Raspberries/Blackberries:
'Redwing' raspberry Photo credit:
Dave Hansen
When selecting which fruits to work on, Bedford says the question the University fruit breeders ask is "Where can we make a difference?"

Sometimes they improve their own releases out of existence. Minnesota varieties like 'Minnehaha' apple, 'Chief' raspberry and 'Trumpeter' strawberry are no longer available, replaced by improved releases from the University's breeding program.

'Autumn Bliss' is the best of the red fall-bearing raspberries. 'Fallgold' takes top marks for the yellow fall bearing raspberry. 'Heritage' is possibly too late for some as a fall-bearing raspberry. (Though fall-bearing will produce a summer crop if canes are not cut down.) Purple-fruited raspberries don't spread like the red ones do. Purple-fruited varieties like 'Brandywine' and 'Royalty' are marginally hardy in zone 4.

Black raspberries, also called black caps, are hard to fruit reliably year after year in zone 4. 'MacBlack' may be the best, though 'Jewel' and 'Bristol' should be considered.

One place the U plant breeders might be able to make a difference is in blackberries. They've all heard the lament that we have wild blackberries in the woods yet no hardy cultivars for home gardens.

The U is working in cooperation with the large blackberry breeding program at the University of Arkansas. U of A has developed a primocane-fruiting blackberry, which means it fruits on the first year growth. As long as the crowns survive, it won't matter if canes are winter-injured as the plants will produce fruit. Arkansas is doing the crossing and the U's program is conducting cold hardiness trials.

The first group of blackberry seedlings were planted last year and will be evaluated this year. Selections will commence. They anticipate at least 5 years of field trials until they're confident in their results and certain the crowns won't die out. Mild winters actually delay trials. Plant breeders are generally among the small minority who complain if it doesn't get down to -25 degrees F. at least once during the winter. Fortunately, Grand Rapids generally has colder weather, so the breeders make use of the North Central Research and Outreach Center there to obtain more frequent test of winter hardiness.

Gooseberries and currants:
'Redlake' currant Photo credit:
Dave Hansen
Gooseberries and red, white and black currants are unfamiliar to many northern gardeners. For years they were banned in Minnesota because they are an alternate host for white pine blister rust, so we're less accustomed to use them. Maybe it's the "beard" on the fruit? (They're a pain to clean.) Black currants are an especially a good source of vitamin C and have been popular in England for that reason. Now, a visitor to England can revel in black currant jam on toast or drink Ribena juice drink, made from black currants (and now also available made from blueberries!) http://www.ribena.co.uk/index_flash.html

'Red Lake' is a widely available red currant, a U of M release. 'Rovada' is also recommended. 'White Imperial', 'Primus' and 'Blanka' get the nod among the white. Good choices for black currants include 'Consort', 'Titania', 'Crusader' and 'Ben Sarek' which are resistant to white pine blister rust. 'Hinomaki Red' and 'Pixwell' are recommended gooseberries.

Peaches:

Ah, peaches! Bedford waxes rhapsodic about fresh peaches. A reliably hardy, full-flavor peach is his holy grail. He's tried some crosses. A while back he planted 300 seeds from South Dakota. Unfortunately, they were all pretty similar. Peaches are self- fruitful so they come fairly true to type from seed. That makes it hard for plant breeders who would like to see some variability. With a laugh, he says he needs to find a wild peach hardy that to -30 with poor flavor to give him something to cross with to breed for flavor.

At one point, Bedford entertained notion of growing peaches as short trees that could be easily covered for winter protection. Unfortunately, the trees suffered winter injury, cankers and gummosis. Gummosis refers to the rubbery sap that seeps out of wounds.

Bedford says a perfect peach should be so juicy that it needs to be eaten over the sink. Unfortunately, many supermarket peaches fail miserably. That may change. The peach industry has discovered that standard cooler temperatures may actually cause mealiness and breakdown of the fruit. This range of temperatures has been dubbed the "killing zone" and the temperature range is 36-46 ° F. Some California growers are now moving fruit from the field to storage at 68 ° F for 12 to 48 hours, then moving them into storage at 32 to 35° F. This pre-conditioning helps alleviate poor quality. Expect to see marketing for this pre-conditioned fruit in store in the future.

Plums:
'Alderman' plum
'Meteor' cherry
Photos:
Dave Hansen
Most of the hardy hybrid plums need a cross pollinizer. The Minnesota plums are not self fertile and often do not have enough pollen to cross pollinate each other. That's why a good pollinizer like 'Toka' is advised. 'Toka' tends to bloom a bit ahead for cultivars but there is usually enough pollen left when they bloom. Wild plums are an excellent pollinizer of cultivated varieties. Bedford pulled out a list with pollen production by cultivar. (The list was from a number of years back, and many of the older cultivars are no longer available and the newer not included.) Two others that could be used as weak cross pollinizers are 'Superior' and 'Ember'.

'Mount Royal' is the only reliably hardy European plum for zone 4. It's self-fertile so it doesn't need a pollinizer. European plums are used for dried plums (formerly known as prunes). They're sweet, low acid and edible right off the tree.

Plum and cherry trees aren't long lived trees-you can expect only about 15 to 20 years out of these trees.

Cherries:
There are no fully hardy sweet cherries for Minnesota. 'North Star', a naturally dwarf tree, and 'Meteor' are hardy tart cherries that were developed by the U of M. 'Mesabi' has also proven itself in the Minnesoata climate. The 'Bali' or 'Evans' cherry (same cherry is a newer hardy tart cherry that has been touted as being much sweeter than others. or " Bedford says he has not tasted enough fruit yet to confirm these claims.

Bedford hears from amateur fruit growers who report their experiences. ' Lapins' is an older sweet cherry cultivars that has supposedly survived -29° F. and produced spring flowers. Another grower has had luck with 'Gold', a yellow-fruited variety.

Pears:
'Comice' pears are Bedford's favorite pear for eating. For years they were available only in holiday gift boxes. They're more generally available these days. They need after ripening to reach their peak. 'Bosc' and 'Summercrisp' should be eaten while crisp. (Note: 'Comice' and 'Bosc' are not hardy here. Hardy pears include 'Summercrisp', 'Golden Spice', 'Gourmet', 'Luscious', 'Ure', 'Parker' and 'Patten'.)

Most pears should have a buttery, juicy texture when they are ready to be eaten. They are shipped hard so when you shop for pears, don't look for color, buy them green and leave them on the counter until the stem end gives a little when pressed. Don't leave them until the body gets soft as they'll be mush. 'Summercrisp', 'Bosc' and all Asian pears should be eaten while they are crisp.

Most pears, except the crisp textured varieties listed above, need after-ripening as they're mature but not yet ripe. The pear industry is investigating packaging pears in atmosphere controlled packaging with some type of indicator, a litmus test, for ethylene, to indicate ripeness. (Ethylene is the gas given off by ripening fruit.)

If you are an amateur fruit grower and would like to join with like-minded souls, check out the North American Fruit Explorers website. http://www.nafex.org/

Minnesota Blues
David L. Hansen, Professor, Director MAES Photo Center, Minnesota Agricultural Experiment Station

'Northcountry'; blueberry Photo credit:
Dave Hansen
“Winter protection and soil are the absolute keys to blueberry success” says Jim Luby, director of the University of Minnesota, Agricultural Experiment Station’s fruit breeding program. Northern Minnesota’s pick-your-own blueberry farms testify to the potential of this unique crop, native to North America.

While it is difficult to make a go of a commercial blueberry farm, home gardeners shouldn’t be discouraged. Anyone who has sampled fresh picked blueberries from the boreal forest knows the rich taste of this fruit. For home gardeners another plus is the plant’s landscape value; attractive white blooms, green and then blue fruit, and fall color of deep red and burgundy in the thick, glossy leaves.

Minnesota-bred blueberry varieties such as Northblue (1983), Northcountry (1986) and the more recent Polaris and Chippewa, both introduced in 1996, are known as half-high types. They reach from 18 to 40-inches high at maturity and depend on snow protection to survive the winter, as part of the bearing surface is hopefully covered by snow.

Compare this with their 6-to-8 foot high-bush eastern cousins found along the Atlantic coast, from Nova Scotia to New Jersey and further south. High-bush berries that are machine harvested are used for processing. They are more delicately hand-harvested for fresh sales, and these large berries are the ones most often found in supermarkets. Many consumers feel the rich, original blueberry taste is missing from these oversized berries. To complete the blueberry spectrum, the low-bush type - with small, pea-size fruit – has evolved in our cold northern climate. The acidic soil under northern pine and fir stands are ideal for low-bush, native blueberries, and the forest cover provides needed winter protection. Managed native stands of low-bush are harvested in Maine and eastern Canada and the tiny fruits used in yogurt and muffins, where a large berry would be an unwelcome glob.

Development of half-high plants combing the productivity of the taller bushes with the hardiness of shorter ones was initially attempted in New Hampshire in the 1940s. The project proved too much of a challenge and no cultivars were released.

Cecil Stushnoff, from Saskatchewan, initiated the University of Minnesota blueberry program when he arrived in 1967, with the goal of developing cold-hardy, half-high, high-quality, large-fruited cultivars. Some of the original parents were plants that had been collected and grown by others at several University sites before that. In 1973 Stushnoff partnered with David Wildung from the University’s North Central Research and Outreach Center at Grand Rapids, to consolidate the trials there.

The Grand Rapids station is the coldest horticultural research center below the Canada-U.S. border, and provides a tough test for fruit crops. Temperatures of -40° F/C are extreme, but even average winters typically reach -30° F. Wildung confirms that snow cover is essential for blueberry survival, “In 1996 we had 50 degrees below (Fahrenheit) but there was three feet of snow on the ground. The next summer was one of the best crops we ever had. But if there is no snow cover they can be badly hurt.” A second blueberry testing site was set up in the 1970s at Becker, Minnesota, a new research station on the sand plain in central Minnesota, where irrigation is essential.

In 1981 Stushnoff moved to the University of Saskatchewan, Saskatoon, where he became head of the horticulture department, and Jim Luby became director of the Minnesota program. Over several decades the breeders collected native plants from Minnesota, Wisconsin, Michigan, New York, Massachusetts, Manitoba and New Hampshire and incorporated them in the breeding program. The Minnesota program is the primary developer of blueberry cultivars for cold climates, and six varieties have been released to commercial nurseries (see table). Private nurseries are licensed to sell the plants to the public as the University does not deal in direct sales.

In addition to winter hardiness and plant stature, researchers look at and evaluate a long list of characteristics when searching for a new variety. This includes: bloom time, ripening date, ripening uniformity, vigor, fruit size and color, size of picking scar and firmness.

“Blueberries are difficult to propagate,” Luby says. The most successful way is by tissue culture, which requires specialized, sanitary lab conditions but is efficient and produces slightly more vigorous plants.

If you are contemplating growing this crop, soil preparation and winter protection is essential. “But this work is balanced by the fact that blueberries have very few pest and disease problems, so no spraying is necessary,” Luby says. “And, if you mulch to keep the weeds down, then no herbicides are needed.” Luby also points out that two or more varieties are recommended to insure good pollination.

“Blueberry growing presents a challenge for most gardeners because the plants need specific growing conditions, especially acidic and well drained soils,” says Emily Hoover, University of Minnesota fruit management expert. They grow best in soil with a pH of 4.0 to 5.0. “Blueberry plants are long-lived, so considerable time and effort to prepare the soil is a wise investment. And, this must be done before planting. If the pH is too high, above 7, the plant grows slowly and the foliage turns yellow. If too high for an extended time the plants will die.” And, their roots will quickly suffocate if the water level is within a foot of the surface. Blueberries have a shallow and fibrous root system which requires frequent but light watering, so well-drained soils are essential.

Fall color.
Photo credit:
Dave Hansen
The University of Minnesota Extension Service has a fact sheet available which details soil preparation and other management issues, at http://www.extension.umn.edu/distribution/horticulture/DG3463.html. Basically, soils with a pH greater than 7 are not recommended for blueberries. If the pH is between 5.5 and 7 and the texture is sandy to sandy-loam it may be modified to grow the crop. Mix four to six inches of acid peat into the top six to eight inches of soil. “In addition to acidifying the soil, peat increases the soil organic matter,” Hoover says.

In addition to an acid soil, blueberry plants require soil that is both well aerated and has a high water holding capacity. For a home garden, which typically has soil not suitable for blueberries, a few plants may be grown by excavating a space 15 inches deep by 24 inches wide and long. Replace this with a mix of two bushels well-rotted sawdust, leaf mold, or peat; one bushel loam, and one cup wettable sulfur. “For gardeners,” Luby says, “adding sphagnum peat at planting to improve establishment and growth is beneficial in almost any soil.”

You’ll want to locate the plants in a sunny location, for best productivity. Think ahead to provide a structure, such as a hedge, to serve as a snow fence. The goal is to model a farm windbreak, which will cause drifting snow to accumulate on the lee side of the structure and cover the blueberries. A few plants in a garden or yard can easily be covered with straw and then just shovel snow over them as winter progresses. Plants from the Minnesota program are hardy down to about -30° to -40° F or Zone 3a on USDA maps, thanks to 10 years or more of testing each variety at the Grand Rapids station. Unfortunately, growing blueberries on the exposed prairie will be a challenge. As North Dakota State University horticulturist Ron Smith says, “Blueberries can only be grown with Herculean effort in North Dakota.” After 35 years of working with the crop, Minnesota’s Dave Wildung offers another view, “If you guarantee me snow cover I’ll guarantee you blueberries!”

Berries are formed on one-year-old wood, with good yields coming in about the fourth year. So, after about five years some pruning should be done to remove dead branches, shape the bush, and stimulate new shoot growth. Removing dead or dying branches will also help avoid the chance of disease. The plants tend to overproduce, resulting in small, late-ripening berries and plants with little new growth. To avoid the problem remove most of the thin, weak branches that have many flower clusters but few leaves.

Another challenge - don’t there seem to be many! – is competition from wildlife. “Birds love the berries and are happy to sample them before you do,” Luby says. “So, you’ll need to protect the fruit unless you just love to feed wildlife.” The best way is to cover the plants with netting, leaving no edge open for birds to get in. Fruit ripens over a three-week period so you’ll have to remove the netting several times to pick the berries. A final word of warning from the experts; rabbits and deer may eat young branches during the winter, so use fencing or netting as protection.

The fruit breeding program of the Minnesota Agricultural Experiment Station has over 100 years of major successes. Information about the other 300 horticultural releases from the University of Minnesota is available at: www.maes.umn.edu/MNHardy/. This includes the amazing Honeycrisp apple. This sweet-tart variety has a storage life of six months and is extremely cold hardy, which helps explain why there are over two million trees growing in North America.

University of Minnesota, half-high blueberry cultivars

(note: yields are collected from zone 3b, reduce up to 50% for zone 3a)
cultivar plant characteristics1 fruit yield fruit characteristics
Northblue 20-40 inches tall
30-60 inches wide		 3-12 lb./plant Large, dark blue, firm berries; good fresh flavor; superior processed flavor.
Northsky 20-40 inches wide
10-30 inches tall 		1-5 lb./plant Medium, sky-blue berries; sweet, mild, aromatic fresh flavor; superior processed flavor. Ripens with 'Northblue.' Yield and berry size benefit from cross-pollination.
Northcountry 15-40 inches tall
30-60 inches wide 		2-7 lb./plant Medium, sky-blue berries; sweet fresh flavor similar to wild lowbush blueberries; ripens 5 days earlier than 'Northblue.' Yield and berry size benefit from cross-pollination.
St. Cloud 30-50 inches tall
40-60 inches wid		 3-9 lb./plant Medium, dark blue, firm berries; sweet flavor, crisp texture; good storage capability; ripens 5 days earlier than 'Northblue.' Requires second cultivar for pollination.
Polaris  20-50 inches tall
30-60 inches wide		 3-10 lb./plant Medium-large berries; very firm and very crisp texture; intense aromatic flavor; excellent storage capability; ripens 7 days earlier than 'Northblue.' Requires second cultivar for pollination.
Chippewa 20-50 inches tall
30-60 inches wide		 3-12 lb./plant Medium-large berries; sky-blue color; sweet flavor; firm fruit; ripens with 'Northblue.' Yield and berry size benefit from cross pollination.


Little Green Weevils
Jeffrey Hahn, Assist. Extension Entomologist

Polydrusus
Polydrusus damage Photos: Jeff Hahn
Some gardeners have discovered small green weevils on their plants during early May. These weevils are known as Polydrusus sericeus (no common name). Originally from Europe, P. sericeus is a type of broadnosed weevil. They get their name because unlike most weevils that have a conspicuous long slender snout, their snout is short and broad. They are about 1/4 inch long, black, and are covered with metallic green scales. When this weevil is newly emerged as an adult, it will also show some iridescent gold or red color on it. Like other broadnosed weevils, Polydrusus can not fly.

This insect was reported recently feeding on William Baffin rose in the St. Paul area and apple and pagoda dogwood in central Minnesota. This weevil is generally common through out much of northern and central Minnesota. They actually have a broad host range, feeding on the leaves of many hardwood trees and shrubs. They feed by making notches along the edge of the leaves. They are also known to attack buds.

This beetle does not usually occur in high enough numbers to cause severe damage, although it is possible for it to have a high population in a localized area. These weevils are first active in late May or June and can be found through the summer. If you encounter a situation where you would like to manage these weevil, many active ingredients should be effective against them, such as permethrin, esfenvalerate, bifenthrin, cyfluthrin, carbaryl, or acephate. Be sure to select a specific product that is labeled for the plants you wish to treat.



Blister Beetles
Jeffrey Hahn, Assist. Extension Entomologist

Blister beetle Photo credit:
Jeff Hahn
An interesting insect was recently reported attacking the flower blossoms of iris and lupines in large numbers (hundreds) in Wright county. An attractive beetle, they have an iridescent dark green head and wing covers and orange and black legs. They range in size from ½ - 3/4 inches long. This insect is the blister beetle, Lytta sayi (family Meloidae). This insect has no common name.

Like other blister beetles, they have a narrow, elongate body with an ant-like head (wider than the pronotum, the area directly behind the head) and smooth, soft, flexible wing covers. Blister beetles get their name because they contain cantharadin, a substance that can raise blisters when it contacts human skin. Fortunately, the blister beetles you encounter in your garden generally do not have a high enough concentration of cantharadin to be a problem.

Interestingly, the larvae of many blister beetles attack grasshopper eggs. Back in the late 1980's when we endured severe drought, blister beetles became common in response to the high numbers of grasshoppers. Blister beetles belonging to the genus Lytta attack bumble bees and other ground nesting bees.

There are other blister beetles that may be found in gardens, including species that are colored black, gray or are striped. They chew the leaves of a wide variety of plants including peashrub (caragana), alfalfa, and potatoes. If they occur in high numbers, they can cause significant damage to plants. If you need to protect your plants and they are numerous, treat the blister beetles as soon as you notice them. Most garden insecticides are effective including products containing one of the following active ingredients: permethrin, esfenvalerate, bifenthrin, cyfluthrin, carbaryl, or acephate. Be sure the specific product you select is labeled for the plants you wish to treat.

Masked Hunters
Jeffrey Hahn, Assist. Extension Entomologist

Masked hunter Photo credit:
Jeff Hahn
You may occasionally see a masked hunter in your home. A masked hunter, a type of assassin bug (family Reduviidae), is a predator of insects. They especially like bed bugs, although the presence of masked hunters does not necessarily mean there is a bed bug problem.

A masked hunter is about 5/8th inch long and black. It is generally a slender insect with a narrow head. As an adult they have fully developed wings and can fly. All of their legs are about the same size. This is worth noting as masked hunters and leaf-footed bugs (such as western conifer seed bugs) can be confused for each other. However, leaf-footed bugs have back legs that are larger than the rest with a leaf-like or oar-like growth on it.

Immature masked hunters can also be found indoors. They camouflage their bodies by covering themselves with dust and debris. While this insect is brownish, it often appears gray because of this. Masked hunters get their name because of this behavior by the nymphs.

Masked hunters are generally harmless to people but they do have the ability to bite humans if they are mishandled or they feel threatened. In a case recently, a woman was bitten on the foot while in the shower. The masked hunter apparently inadvertently flew into the shower, was knocked down by the spray of water, and instinctively bit the person when it landed on them.

You would typically not see more than one or a small number of masked hunters in a home at a time. Physical removal is the only necessary control (be sure that you handle them carefully to avoid bites). It is possible, but unlikely that a large masked hunter population may be present. If this is true, inspect the premises to determine what insect is serving as a food source for the masked hunters. Reducing or eliminating the food source will control masked hunters.

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


Seeing Spots on Local Maples
Michelle Grabowski, Regional Extension Educator-Horticulture

Anthracnose
Tar spot
Photos:
Michelle Grabowski
There are many different fungi that cause leaf spotting on maple trees. Probably the most common leaf spot of maples being seen in Minnesota over the past few weeks is anthracnose. Maple anthracnose can be caused by several different fungi that all create very similar symptoms. Much like anthracnose in oak and ash, maple anthracnose causes dark brown or black irregular shaped spots to form on the leaves. These are often found close to the leaf veins. As the infection grows, these spots get larger and grow together. In some cases the infection may take over the majority of the leaf, creating a black twisted and crumpled form with only a green stem holding it to the tree. One fungus in the anthracnose group tends to attack the leaf where insect damage has occurred. Because of this fungus, it is common to see anthracnose spots growing close to insect galls on maple leaves. Anthracnose is typically seen in the lower branches and inner sections of the tree where humidity is highest. Although severe infection can cause leaf drop, maple anthracnose is not considered a serious disease problem. Maple trees can tolerate leaf spot and will replace fallen leaves with new ones.

Other leaf spots of maple include Phyllosticta leaf spot and tar spot. Phyllosticta leaf spot causes roughly circular spots with a dark brown or purplish border and a light center. It is sometimes possible to see dark colored fungal fruiting bodies at the center of these spots. Tar spot of maple is caused by the fungi Rhytisma sp. and causes large raised black spots on maple leaves. These spots often start out as yellow to light green areas on the leaf, and then become raised, black, and tar like as the fungus produces fruiting bodies. The large black spot can be either one solid black spot or many smaller black spots located very close to one another on the leaf. A yellow halo sometimes remains around the raised black tar spot. Severe cases of tar spot and Phyllosticta leaf spot may also cause leaf drop, but this does not hurt the overall health of the tree.

The majority of the maple leaf spot fungi can survive the winter in fallen leaves at the base of the tree, in dead twigs or buds. Fall clean up and removal of dead branches and fallen leaves can reduce the amount of fungi available to cause disease the following spring.

Contributors:
Nancy Rose
Patrick Weicherding
Bob Mugaas

By the Snyder bldg. Photo credit:
Beth Jarvis
Lawns:
Are you watering your lawn? To keep the grass just green, you need 3/4" of water per week. To keep it alive, apply ½" every 10 days. These are just "barely there" lawns, not actively growing.

Wind and temperature both drive grass's need for water. The rate of water loss is directly related to wind that whisks away the moisture layer around each leaf. The plant draws water from the roots to replace it. Temperatures of 85° F. plus for several days are stressful to the grass.

Going on vacation? If you have an automated sprinkler system, allow it to cycle somewhat normally. Rain sensors can be installed to keep the sprinklers from running during rainstorms, or when there is ample moisture.

Mow high for season. Long grass blades shade the ground and reduce soil water loss.

When clover blooms, it's a signal to apply post-emergence crabgrass control. The grass is now at a tender, easy-to-control stage. Be sure lawn isn't drought-stressed when you apply the herbicide as post-emergents with MSMA, found in many post-emergence crabgrass products, will injure drought-stressed grass.

Avoid traffic on dry grass. Lawnmower wheels can exert enough pressure on drought-stressed lawns to kill the grass and leave stripes.

'Betty Prior' rose. Photo credit:
Beth Jarvis
Trees and shrubs:
In early June, the first cases of Dutch elm and oak wilt were spotted. If your trees show wilting symptoms, check with your city forester for confirmation.

Water newly planted trees. Water the root zone of established trees.

Psyllid damage looks like herbicide injury–contorted leaves on ash. It might look like aphid damage. Find out what to look for in Be Aware of Psyllids on Black Ash http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-Nov0105.html#psyllid Lots of leaf diseases have been curtailed by the dry weather. Trees should leaf out again. Just keep them well-watered.

However, if you are seeing mature maples, birch and ash dying from the top down, it might be decline resulting from drought stress. Mature trees need to be watered about 1-1.5" per week over 2 applications. A brief watering every day benefits the grass but not the trees. (If your landscape trees were not watered last summer/fall, they might have been drought stressed and were unable to shut down properly for winter. That lead to winter injury and failure to thrive this spring.)

Fruit, Vegetables and Flowers
Deadhead perennials as they finish blooming.

Cage or stake tomatoes if you have not done so.

Mulch garden beds to preserve soil moisture. Wood chips, cocoa bean or other mulches is excellent for perennial beds. Vegetable gardens may be mulched with herbicide-free grass clippings, compost, straw or other easily-degradeable mulch materials.

Editorial Notes

'Pink Pixie' Lilies Photo credit:
Beth Jarvis
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or to unsubscribe, enter: unsub yglnewslist

Gardening questions go to: http://www.extension.umn.edu/askmg

Next issue, we'll have two more "tree legalities" articles. I'll finish up with my visit with David Bedford in July.

Dave Hanson, forester and the guiding light for the Shade Tree Advisor course, will be writing an article some time this summer on growing evergreens in shade. I've asked him to touch on the physiological drawbacks to shade vis a vis incidence of winter injury, among other things.

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/.

Deb Brown answers gardening questions on Minnesota Public Radio's (MPR) "Midmorning" program on the first Friday of every month at 10 a.m. The program is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations. (Scroll down for map.)

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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