Yard & Garden Line News
Volume 1 Number 6; July 1, 1999
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Renovating Junebearing Strawberry Plantings
Doug Foulk, Extension Educator
University of Minnesota Extension Service, Ramsey County
Home strawberry planting after foliage has been removed. All plants outside staked area will be rototilled to reduce row width.
Photo Credit: Doug Foulk
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Once this year’s fresh strawberry shortcake is gone and the last batch of strawberry jam processed, it is time to renovate your Junebearing strawberry patch.
Why renovate? Strawberries are poor competitors, not only against invading weeds, but neighboring strawberry plants as well. As a strawberry row becomes dense with new daughter plants or the row width increases to more than 24 inches, fruit quantity and quality begin to suffer, especially in the center of the row. Renovation helps maintain optimum row width and plant density and removes foliar diseases at the same time.
Renovate Junebearing strawberries as soon as possible after harvest is finished for the season; within 2 weeks is best. The renovation process involves three or four simple steps:
- Mow the foliage
(optional). How dense is the planting? How healthy is the foliage? If you have more than about 5 plants per square foot within the row, or if you observe serious foliar disease, AND you live in the southern two-thirds of the state, remove the foliage using a standard lawnmower or by hand. Set the lawnmower high enough so that the crowns of the plants are not damaged.
Mowing reduces the vigor of the plants, delaying runnering by 10 to 20 days. This delay helps prevent excessive runnering and, therefore, density and row width problems. Because the growing season is too short in the northernmost third of the state to delay runnering, gardeners in the far north should skip this step.
After mowing, add the clippings to your compost pile only if the foliage was healthy. If the foliage was diseased, bury the clippings or dispose them in accordance with local ordinances.
- Narrow the row.
A vigorous planting of strawberries may easily double in row width and density in a single season. Anticipate such growth by narrowing the existing row to a width of 9-12 inches using a rototiller or hoe (figure 1). While such a practice may sound extreme, new daughter plants will soon be produced to create a row of approximately the proper width.
Individual strawberry plants become less productive over time. Fortunately, a simple trick will extend the productive life of your Junebearing planting by several years. When preparing to narrow the row, choose one side of the row to keep, rather than the center. The following year, choose the opposite side, then alternate back and forth in succeeding years. This method requires a small amount of extra space on each side of the strawberry row, but provides an annual supply of newer, more productive plants.
- Remove all weeds.
Now is your best chance to weed, while weeds are easy to spot and to reach. Weeds not only out-compete strawberries, but can also serve as hosts for insect and disease pests.
- Fertilize the planting.
Renovation is the best time to fertilize your strawberry planting. The addition of nitrogen at this time encourages vigorous vegetative growth; the number of leaves a plant possesses as it goes into winter is directly related to the number of fruit that it will produce the next spring.
If you based soil amendments at planting time on a soil test, you only need to apply nitrogen at renovation. Apply a nitrogen source at the rate of ¼ lb. per 100 feet of row. For example, if you use ammonium nitrate, which is 33 percent N, you will apply approximately ¾ lb. per 100 feet of row.
Everbearing (Tribute, Tristar) and dayneutral (Ogallala, Fort Laramie) strawberries do not require renovation. To promote maximum fruit production in these cultivars, remove all runners as they appear. Everbearing and dayneutral plantings grown in this manner will need to be replaced about every three years. Junebearing types that are renovated annually may last a decade or longer before replacement is desirable.
What’s Wrong with My Raspberries?
Doug Foulk, Extension Educator
University of Minnesota Extension Service, Ramsey County
Picnic beetle on raspberry. |
Raspberries are a relatively easy fruit to grow in the home garden. On occasion, however, problems can show up on the fruit during the summer harvest. A careful examination of problem plants should reveal signs and symptoms that will enable you to diagnose what’s wrong and what to do about it.
Picnic Beetles. You may find picnic beetles feeding on berries at harvest time. These beetles are about ¼ inch long, shiny black, and sport two or more yellow spots on each side of the body. Because picnic beetles are attracted to overripe fruit, the solution is simple: keep fruit picked as it ripens and clean up any overripe berries that may fall to the ground.
Fruit Rots. Fruit rots may develop during warm, wet weather. Ripe berries may become soft and watery or become covered with fuzzy growth. Fruit rots, like picnic beetles, usually affect overripe fruit. Again, timely picking and sanitation are the keys to controlling this problem.
Crumbly Berries. When crumbly berries are present, check the rest of the plant. Does it look otherwise healthy? If so, poor pollination may be the cause. Poor pollination is usually the result of cold, windy or rainy weather at bloom time. Pesticides toxic to bees applied during bloom may have the same effect. Do not apply pesticides during bloom.
Virus symptoms on raspberry.
Photo: F. D. McElroy |
If, however, an examination of the plant reveals stunting or yellow, mottled, curled or puckered leaves, then suspect a virus. Raspberries are susceptible to a number of viruses, including raspberry mosaic, raspberry leaf curl and tobacco ringspot virus. Viruses are tricky to diagnose, and may easily be confused with herbicide damage, so consult an expert if you think your plants are infected.
If a virus is the cause, remove all raspberry plants exhibiting symptoms, roots and all. If over half of the plants are affected, remove the entire planting. Because many viruses may remain viable in the soil for years, do not replant in the same place.
When starting a new raspberry planting, always purchase new plants from a reputable source; do not dig up plants from your neighbor’s yard, as such plants may already be infected, even if no symptoms are yet present. If viruses have been a problem in the past, consider a virus-resistant cultivar. ‘Nordic’ is resistant to the aphids that transmit mosaic virus, while other reportedly virus-resistant cultivars include ‘Reveille,’ ‘Canby’ and ‘Haida.’
Bleached drupelets on raspberry.
Photo: M. A. Ellis |
Bleached Drupelets. In some years you may find berries that contain white drupelets. These white drupelets appear individually or in clusters on the berry. The cause is excessive sun or heat during fruit formation. Because bleached drupelets have an environmental cause, control is neither practical nor necessary. Affected berries pose no threat to the health of the planting.
A Banner Year for Bunnies
Deborah Brown, Extension Horticulturist
1999 has been exceptionally good (or bad, depending on
your point of view) for bunny rabbits. For weeks, they
had all sorts of young, tender leaves to feed on. But
once rains become less frequent and hotter temperatures
help plants mature and toughen, the tastiest, most
tender and succulent greens will be found in your
carefully watered garden....and in mine!
What's a person to do? Many home remedies have been
tried; most with limited success. Some methods
gardeners swear by include mothballs or bloodmeal
spread on the soil, hot pepper sauce and detergent or
store-bought repellant sprayed on the leaves, or
perhaps a lively cat or dog to patrol the yard.
While bloodmeal may repel small animals, it may attract
some larger ones -- dogs or raccoons. And any
repellant that's sprayed on the foliage must be
reapplied frequently since rainfall and sprinkling will
wash it off.
In fact, the only sure-fire way to keep the bunnies at
bay is to surround your garden with a wire mesh fence
pushed several inches into the soil and extending 24
inches above ground. (Most people can step over it
without too much difficulty.) To be an effective
barrier, the mesh should be no larger than 3/4 to an
inch in diameter. The fence won't be beautiful, but
your plants will!
And Now, a Corny Moment
Deborah Brown, Extension Horticulturist
Block planting of sweet corn.
Photo credit: Deb Brown
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Which summer vegetable should grow "knee high by the
fourth of July?" In honor of everybody's favorite, the
one that's right up there with motherhood, apple pie,
and the American flag, here are some tidbits (or should
we say, `niblets') of sweet corn information:
* It takes two to tango: Corn has separate male and
female flowers; the tassel atop each plant is made of
males, the ears below, females.
* Plant corn in blocks, rather than one or two long
rows in your garden. That way wind can easily spread
pollen from male flowers to the female silks. Each
pollinated female develops into a ripe kernel; without
pollen, kernels never enlarge.
* "Baby corn" is prized for stir-fry. Just pick 'em
early, before they expand. To grow sweet corn
specially for this purpose, plant seeds only 6 inches
apart, or choose a special mini-corn variety such as
`Minor'.
* Try the milk test: Sweet corn is ripe when silks
turn dark, and kernels release thin, milky liquid when
pierced.
*Sugars are much slower to turn starchy in new
"supersweet" varieties. You'll find they're still good
a week after harvest.
* If you're not growing one of the sugary varieties,
put the water on to boil when you go out to pick it; it
will never again taste as sweet. If you can't cook corn
right away, refrigerate it, but use it fast.
Attend to Those Houseplants
Deborah Brown, Extension Horticulturist
Time to re-pot?
Photo credit: Deb Brown
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It's time to take a break from outdoor gardening and
focus your attention briefly on houseplants. Warm
summer weather means you can set up a card table on a
shady deck or in the yard, under a tree, to work on
your plants without worrying about messes.
Because of longer days and increased light, many
houseplants have grown enough to require repotting.
Choose pots only one size larger than currently in use.
Put an irregularly shaped pebble over the drain hole to
keep soil in, but allow excess water out. Add fresh
potting soil, transfer the plant -- roots, soil, and
all -- then firm more soil gently between the root ball
and sides of the container.
If you've any houseplants that suffer from stubborn
pest problems, it's easy to treat them with insecticide
outdoors, then bring them indoors once they dry.
Whether you spray with a chemical pesticide or an
insecticidal soap, keep the plants out of bright
sunlight for several days after spraying to minimize
the chances of injury.
Keeping Cut Flowers Longer
Deborah Brown, Extension Horticulturist
Photo credit: Deb Brown
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The season for beautiful flowers outdoors is in full
swing. Why not take advantage of Mother Nature's
generosity by enjoying bouquets of flowers indoors,
too?
One thing is certain; whether your flowers are
`homegrown' or `storebought' you want them to last as
long as possible once you bring them indoors and
arrange them. Here are a few suggestions for getting
the most out of your cut flowers.
Just as you would assemble the freshest ingredients to
make a great salad, start with the freshest flowers you
can find to make a great bouquet or arrangement. That
usually means choosing flowers that are just opening
rather than in full bloom.
Pick flowers from your own garden early in the morning
before heat and sun start depleting their moisture
content. If you're really serious about freshness,
carry a clean bucket of water with you to hold cut
flowers as you gather more.
The large farmers' markets in downtown St. Paul and
Minneapolis have become an increasingly good source of
both potted and cut garden flowers. Visit them early
Saturday or Sunday morning for flowers harvested in the
cool of the evening before.
Ask your florist or the attendant at the flower section
of your local grocery store when they receive shipments
of fresh flowers, then time your purchases accordingly.
Once the flowers are in your kitchen, strip off any
foliage that will be under water in the vase. You
might choose to remove a portion (but not all) of the
foliage above the vase, too. Lots of moisture will be
lost through the leaves, and visually, too many leaves
can overwhelm the appearance of the flowers, especially
when blossoms are small or delicate.
Cut each stem on an angle so it won't sit flat inside
your vase or container. It's best to make the cut
under water so air bubbles can't clog the conductive
tissue responsible for drawing moisture through the
stem.
The easiest way to do this is to hold the stem in a
slow stream of lukewarm water from the tap while you
cut it with a sharp knife. A drop of water will cling
to the bottom of the stem as you transfer it to a
container.
Clean your vase or container carefully before putting
fresh flowers in it. Use a bottle brush and hot soapy
water to remove all traces of past use, then rinse
thoroughly. If you can't fit a brush into the vase,
drop in a foaming denture cleaner instead, and let it
sit overnight before rinsing.
Fill the container with slightly warm water and add
some floral preservative in the form of powder or
liquid drops. While home nostrums such as copper
pennies or aspirin do nothing to improve your flowers'
longevity, well-documented research has proven that
commercial floral preservatives can add many days to
the vase life of most flowers.
Place cut flowers out of direct sunlight and away from
heat. The cooler you're able to keep them, the more
slowly they'll mature.
Maintain the original water level in your vase by
adding more water and preservative mix. And when the
flowers start to fade? Toss them onto the compost
pile. It's time for the fun of picking or buying a new
bunch!
This Strawberry Blite Is No Disease!
Beth Jarvis, Yard and Garden Line Project Coordinator
Strawberry blite is the common name for a somewhat uncommon plant. Every year the Yard and Garden Clinic gets a few inquiries about a plant that has leaves similar to lamb's quarter but fruits more like strawberries. It's called strawberry blite or spinach, Indian paint or Indian strawberry.
Botanists know it as Chenopodum capitatum. In some references it's listed as Blitum capitatum but one look at the roughly triangular leaves will tell you it's a member of the goosefoot family. This 6" to 24" tall plant is found in waste ground and recently burned clearings. It grows in Canada and the northern US as well as Europe.
Perhaps the most noticeable feature of this plant is the flower head, which is a compact, red, marble-sized cluster of small flowers. In summer, the plant is adorned with these flower heads borne either singly or in clusters of two or three along the stems.
The tender, green growth can be cooked and eaten. Late summer, the fruit is edible though "insipid' in flavor but quite nutritious.
Colorado Potato Beetles
Dave Ragsdale, Professor, Economic Entomology,
Jeff Hahn, Assistant Extension Entomologist
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| Photo credit: Minnesota Extension Service |
Colorado potato beetles, also known as potato bugs, are very familiar to home gardeners.
Adults are about 1/4 inch long, convex-shaped, and are burnt orange in color with ten black
stripes on their forewings. They lay bright orange-colored eggs on the underside of leaves,
which hatch into humped-backed purplish or reddish larvae. Colorado potato beetles usually
have two generations each year. The different stages overlap and all stages may be seen on
potatoes at a given time.
Both adults and larvae feed on potato leaves. Larvae tend to be gregarious and stay on or near
the leaf where they hatched for the first two instars. The majority of the feeding done by
larvae occurs in the last larval instar. Potatoes usually can tolerate more defoliation when they
are in the vegetative stage and are most sensitive to defoliation when tubers are beginning to
bulk. Tuber bulking begins soon after flowering, thus beetle control is most critical right after
flowering. Plants in the vegetative stage can tolerate 25% defoliation but only 10%
defoliation during tuber bulking.
Control of Colorado potato beetles is challenging at best. Handpicking is the best bet,
especially in small gardens. Be sure to pick off not only the adults and larvae but also the
orange eggs on the underside of leaves. New adult beetles can fly into the garden so be sure to
check your garden regularly.
The Colorado potato beetle has plagued potato growers for over 130 years. This insect has an
extraordinary ability to develop resistance to insecticides. Indeed, this one species has become
resistant to over 60 different compounds. Virtually all of the synthetic organic insecticides
available to home gardeners for Colorado potato beetles (e.g. carbaryl [Sevin], rotenone,
methoxychlor, and permethrin) are materials that will likely fail to provide any control. Beetle
resistance is a function of pervious history of treatment and proximity to commercial
production.
One compound that does provide some control is a material based on a protein toxin
produced by the bacterium, Bacillus thuringiensis var. tenebrionis (may be also be found as
Bacillus thuringiensis var. sandiego; sold as M-One or Colorado Potato Beetle Beater). This
product can control young Colorado potato beetle larvae (1st and 2nd instars) but does a poor
job on larger larvae and adults. Colorado potato beetles have not developed resistance to this
toxin. To be successful in controlling Colorado potato beetles in home gardens, you have to
apply this product frequently, and physically remove large larvae and adults.
This product may be difficult to find, but some garden centers may carry it. Also, check mail order catalogs, such as Gardens Alive.
Fungus-Killed Flies
Jeff Hahn, Assistant Extension Entomologist
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Photo credit:
Jeff Hahn |
Flies have been found on different trees, shrubs, vegetables, flowers and other plants. They
look like they are `chewing, sucking, or boring' into leaves or other plant parts. However, if
you look at them closely, you'll discover that not only are the flies not moving but they're
dead, killed by insect destroying fungi.
These flies are known as seedcorn maggots. They are about 1/4 inch long, a little smaller than
house flies, and have small, light-colored patches on their abdomen. Seedcorn maggots can
become infected by a fungus that feeds on and eventually kills them. This is more common
when we experience wet springs.
You can identify fungus-killed flies because their bodies and legs are often at odd, awkward
angles. If you look closely you can sometimes see whitish fungal filaments coming out of the
fly's body. No control or action is necessary. Despite the circumstantial evidence, these flies
are not responsible for holes in leaves, dead twigs or other damage to plants.
Ash Leaf Curl Aphids
Jeff Hahn, Assistant Extension Entomologist
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Wooly aphids on ash
Photo credit:
Jeff Hahn |
Twisted, curled leaves have been common on ash this year. This is the result of the feeding of
ash leaf curl aphids, a type of woolly aphid. If you uncurl the disfigured leaves, you will see
aphids as well as white, waxy material that the aphids produce.
Ash leaf curl aphids also produce large amounts of honeydew which covers leaves, branches,
and other nearby objects. Honeydew is a waste product that aphids produce while they are
feeding which is also attractive to ants.
Despite the appearance of the misshapened leaves, these woolly aphids do little actual harm
to ash. Relatively few leaves are likely to be affected and those that are curled are still able to
photosynthesize. Ash leaf curl aphids are regulated by natural enemies and should not be
common on a particular tree more for more than a year or two.
An application of a systemic insecticide, such as acephate (Orthene) or dimethoate (Cygon)
would effectively manage these woolly aphids. Insecticides, however, do not affect leaves
already disfigured; they remain curled for the rest of the season. Be careful not to over apply
insecticides to avoid negatively affecting natural enemies.
Rose Chafers
Jeff Hahn, Assistant Extension Entomologist
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Rose chafers
Photo credit:
Jeff Hahn |
Rose chafers are slender beetles, about 1/3 inch long. They have tannish or greenish bodies,
long, spiny reddish legs and soft, leathery shells. Rose chafers typically emerge as adult beetles
starting in late-May and are common throughout June. They live about a month with only
one generation a year. You typically find rose chafers in areas of sandy soil (that's where they
prefer to lay eggs).
It is common for rose chafers to suddenly appear in a garden in large numbers. They feed on
the leaves of a wide variety of flowers, fruits, and vegetables. They skeletonize leaves (feeding
on one layer of leaf tissue, except for the veins) giving foliage a transparent and lacey
appearance. Later, damaged areas turn brown. They also love to chew ragged holes on flower
blossoms, especially peonies and roses, and can be found feeding on the fruit of grapes,
strawberries, and raspberries.
You can keep rose chafers away from your plants by setting up a cheesecloth barrier around
your garden, making it taller than the plants. Rose chafers fly over the barrier but do not land
inside. If you don't use a barrier, try handpicking and destroying small numbers of rose
chafers. If you find too many to handpick, try an insecticide, such as acephate (Orthene),
permethrin, carbaryl (Sevin), or malathion. Most rose chafers should be done feeding by the
end of June.
Expect Apple Maggots Now
Jeff Hahn, Assistant Extension Entomologist
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Apple maggot damage on apple
Photo credit:
Dept. of Entomology |
People who grow apples should prepare for apple maggots. This destructive pest of apples is
active from July through September. Adults flies emerge from the soil to lay eggs in apples.
Apples can become misshappen and the flesh can turn brown and rot due to apple maggots.
There are several methods to manage apple maggots. The most effective control is regular
insecticide sprays once every ten to fourteen days starting July 1. However, you can reduce the
number of sprays and still obtain similar results by checking for the presence of apple maggots
around your trees. You can do this by placing one sticky sphere trap on the south side of each
tree. Spray the tree whenever there two to five apple maggots are found on the trap.
You can buy sticky sphere traps through gardening catalogs and garden centers. You can also
make them at home by using a ball about three inches in diameter, colored red or black and
coated with a sticky substance, such as Tangle Trap. It is not important what the ball is made
of, as long as it mimics apples in size, shape, and color.
Another spray schedule you can try is to treat apples two days after a rainfall or a watering of
1/2 inch or more (Do not treat before July 1 and do not spray more often than ten to fourteen
days). Apple maggots are more likely to emerge from the soil when the ground is wet. You
can reduce insecticide treatments by spraying at this rate, although your results will probably
not be as effective as regular calendar sprays.
Effective insecticides for managing apple maggots are phosment (Imidan),
diazinon, and carbaryl (Sevin). Always read pesticide label information carefully before buying pesticides and again.
If you choose to manage apple maggots without insecticides, you can try to trap them out with
sticky sphere traps in your trees. Place one trap for every 100 apples or about five traps in an
average standard tree. This can provide decent control, but it is unlikely to be as effective as
insecticides.
Watch for Squash Vine Borers in the Garden
Jeff Hahn, Assistant Extension Entomologist
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Squash vine borer damage
Photo credit:
Dept. of Entomology |
Squash vine borers love squash, pumpkins, gourds, cucumbers and muskmelons. If your
plants suddenly start to wilt, be suspicious of squash vine borers. You can verify their
presence by looking closely at the stem; if you notice an orangish or greenish sawdust-like
material oozing out you can confirm borers. The trick is to prevent the damage from getting
to this stage because once there, its most likely too late to effectively manage them.
Usually an insecticide application is necessary to protect plants from borers. Your best bet is
an application of carbaryl (Sevin) dust. Consider this especially if you've had trouble with
borers in the past. Treat developing vines weekly, starting when vines begin to run (about late
June or early July). Continue treatments until the end of July.
Because squash vine borers emerge the end of June or early July, you can try a second planting
of summer squash in early July. Squash vine borers are done laying eggs when the second
planting is vulnerable. An option to consider next year is planting resistant varieties, such as
`Waltham' butternut squash, to deter borers.
If your plants do become infested, you may be able to save your vegetables if damage is not too
severe. Slit the stem with a sharp knife and kill the borer. Try to encourage root development
by covering the stem with moist soil. This doesn't always work but you have nothing too lose.
Get the low down on this month's insect pests at Insects http://www.extension.umn.edu/projects/yardandgarden/Ent.htm
Yellow Patch of Turf
Crystal Floyd, Plant Pathology Technician
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Yellow patch on lawns
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Yellow patch, also called cool-season brown patch, is a turf disease which occurs during cool, wet periods in the spring and fall. This fungal disease, caused by Rhizoctonia cerealis, is not common but may be seen frequently during wet years. Rhizoctonia survives winter on plant debris in the soil. During wet periods, the fungus becomes active and is transported by water movement to healthy areas of the lawn. The fungus infects healthy roots causing them to turn brown. Eventually, the blades of infected grass whither and turn yellow or brown in color. The most noticeable symptom of yellow patch is the resulting yellow to brown circular patch of grass. Yellow patch is a difficult disease to diagnose because it looks similar to many other diseases. Laboratory examination is necessary for correct diagnosis.
The best way to prevent yellow patch is through proper cultural practices. Mow grass regularly to maintain a height of 2½ to 3½ inches. Aerate compacted soil in the spring or fall. Dethatch lawns in the spring or fall. The thatch layer should not exceed one-half inch. Water during dry periods and fertilize as needed. Excess nitrogen can increase the severity of yellow patch and other diseases. Fungicide application may be used in conjunction with cultural practices. Thiophanate-methyl (Cleary’s 3336) and chlorothalonil (Daconil 2787) are registered for control of yellow patch. Carefully read and follow all label instructions.
Gray Mold of Strawberries and Raspberries
Chad Behrendt, Extension Plant Pathologist
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| Strawberry botrytis |
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Raspberry botrytis
Photo credit:
Dept. of Plant Pathology
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As our delightful strawberries and raspberries continue to develop and ripen, fungi are diligently working to rot them. Gray mold, one of the most common fruit rot fungi, appears as a gray velvety growth on the infected fruit. Berries in contact with the ground or other berries are usually the most commonly infected.
Gray mold survives the winter on dead plant material and becomes active in the spring. This disease tends to be at its worst during frequent rains or in plantings with high humidity and poor air circulation. As a result of the frequent rains this year, gray mold may appear more often.
Although gray mold infects berries while they are on the plant, it can also rot berries in transit, at the market, or in storage. Therefore, berries appearing normal at the time of harvest may end up rotten only a few days later.
If you are picking or buying strawberries or raspberries handle them carefully, since gray mold readily infects bruised berries. To help prevent gray mold, avoid bruising berries while handling, discard moldy berries, and avoid picking berries that appear to be discolored. Refrigerate berries soon after picking to slow the growth of potential gray mold fungi.
If you are growing raspberries or strawberries you can help prevent infection and reduce fruit rot by thinning overcrowded plants, controlling weeds, fertilizing properly, mulching to create a barrier between the fruit and soil, and watering plants at ground level early in the day. At the end of the season remove and destroy all infected debris to reduce winter survival. Although it may be too late to apply some of these control measures this year, they can and should be applied at the beginning of next season.
Wilting Elms
Chad Behrendt, Extension Plant Pathologist
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Flagging of elm
Photo credit: Robert Blanchett
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Every year, yellowing leaves and dying elm trees plague homeowners and city foresters. Even though Dutch elm disease is not native to the United States, it is a well-recognized disease that has devastated many beautiful urban streets. People may have the idea that this disease is becoming less severe, but Dutch elm disease continues to infect and kill elms. This year is no exception; there are more elms marked for removal in Minneapolis this year than there were last year at this time. However, the continued loss of elms is not a reason to discontinue city programs and management practices.
Dutch elm disease is a fatal vascular wilt disease of elm trees. New infections begin each year in spring to early summer as fungi are dispersed from infected trees to healthy trees by bark beetles carrying the fungus or through root to root contact. Once the tree is infected it tries to defend itself by producing inhibitory defense compounds in the vascular (xylem) tissue. These compounds plug the tissue and block the flow of water, causing the tree to wilt.
Symptoms initially appear in the upper canopy of the tree as wilting, yellowing, and/or browning leaves. Wilted leaves eventually fall from the tree. However, leaves may sometimes wilt, shrivel, and brown without turning yellow. To conduct a quick on-site diagnosis of Dutch elm disease, examine the inner bark for brown streaking. Laboratory analysis can be performed on questionable trees.
Although this disease is fatal to elm trees, it can be successfully managed and controlled through a combination of practices. These practices include surveying and inspecting healthy trees for new infections, sanitation and removal of infected trees, disruption of the below-ground root grafts with a vibratory plow, preventative and curative chemical injections, and the use of resistant cultivars.
Monitoring healthy trees for new infections is one of the most important and effective management practices available. Early detection allows time for therapeutic pruning and curative chemical treatments. In addition, early detection allows for prompt removal and disposal of infected elms, which helps prevent large populations of bark beetles and overland transmission of the fungus. To identify newly wilted trees, look for yellowing leaves in the upper canopy of the tree daily. As the symptoms progress leaves will turn brown and fall from the tree.
If you wish to prevent your valuable tree from becoming infected, you may have your tree chemically injected. Two chemicals are listed for control, Arbotect and Alamo. Arbotect is proven effective, while Alamo is still experimental.
Finally, the best hope for tomorrow is to plant a resistant elm. There have been a number of resistant cultivars developed and several of them are available. However, some of these cultivars are marginally hardy in northern climates, so choose cultivars known to be hardy in your region. Some of the resistant cultivars include ‘Sapporo Autumn Gold’ (University of Wisconsin), ‘New Horizon’ (University of Wisconsin), ‘Valley Forge’ (U. S. National Arboretum), ‘New Harmony’ (U. S. National Arboretum), and ‘Accolade’ (Morton Arboretum). For more information on form, resistance, hardiness, and availability contact the University of Wisconsin, U.S. National Arboretum, the Morton Arboretum, or the University of Minnesota.
Unusual or infrequent diseases observed this June:
Ash Rust: Ash rust is a fungal disease that infects the leaves, petioles, or stems of ash trees causing a orange powdery mass to appear on infected tissue.
Phomopsis canker on dogwood: Phomopsis is a fungal pathogen that causes death and decline of the dogwood. This disease forms a sunken, grayish canker, which girdles the branches or main stem causing wilting and death of the associated foliage.
Test your diagnostic savvy monthly with Disease Watch at: http://www.extension.umn.edu/projects/yardandgarden/Plpa.htm
Editorial Notes
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Daylilies in bloom
Photo credit: Beth Jarvis
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The daylilies are intended to add nothing more than a touch of color.
This issue wound up with a strong fruit focus, at least strawberries and raspberries. While even the late producing strawberries are past their peak here in the Twin Cities, the strawberry harvest is in full swing in greater Minnesota. In my yard, the raspberries and blueberries are in full production and the gooseberries are ripening.
Deb Brown will be the regularly scheduled guest on Minnesota Public Radio's MPR) "Midmorning" program on the first Thursday of every month. Katherine Lanpher hosts the program that is broadcast on KNOW 91.1 FM, and available state-wide on the MPR news radio stations. Although she's been a guest at MPR numerous times, she'll start as a regularly scheduled guest on July 2.
In upcoming issues, our guest authors will be writing about using low maintenance grass mixes, care and maintenance of marginal hardy trees and shrubs, selecting the right root stock for apple trees, and the Minnesota Mum Project. Watch for them! If you have suggestions for
other topics, please let me know!
Back issues Yard & Garden Line News are on the Yard & Garden Line home page at www.extension.umn.edu/projects/yardandgarden/. Our newly revised 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.
If you have gardening questions, please call the Yard & Garden Line at (612) 624-4771.
We publish the Yard & Garden Line News twice a month during the gardening season, on
the 1st of the month and the 15th of the month.
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.
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:
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Happy gardening!
Beth Jarvis
Yard & Garden Line Project Coordinator
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Home strawberry planting after foliage has been removed. All plants outside staked area will be rototilled to reduce row width.
Picnic beetle on raspberry.
Virus symptoms on raspberry.
Bleached drupelets on raspberry.
Block planting of sweet corn.
Time to re-pot?
Photo credit: Deb Brown
