Yard & Garden Line News Volume 2 Number 15                                                              September 1, 2000

Features this issue: Add Beauty to Your Landscape; Plant Evergreens Fall, An Excellent Time To Control Those Persistent Perennial Weeds Controlling Wasp Nests Aphids on Black-eyed Susan (Rudbeckia) Aster Leafhoppers Black Willow Aphids Tortoise Beetles in Gardens Editorial Notes

Add Beauty to Your Landscape; Plant Evergreens
Deborah Brown, Extension Horticulturist

Frosted pine. Photo credit: Beth Jarvis

Evergreen trees lend beauty and interest to the landscape year-round. It's always reassuring to see the soft, pale green "candles" of new needles develop and expand each spring. And in summer's heat, evergreens provide a cooling touch (and fragrance) of the north woods.

But it's during winter, when trees and shrubs are dormant and the only flowers we see are indoors, that evergreens really come into their own. The contrast of sparkling new snow on dark pine or spruce trees turns Minnesota landscapes into "living Christmas cards" and relieves the monotony of all that white and grey.

Take a walk around your yard to decide where you might add new evergreens or replace undesirable specimens.

Perhaps you could use a row of 'Techny' arborvitae to create a privacy fence or define a specific area within your yard. Or maybe you'd like to enjoy the bird song that's sure to follow when you plant a spruce within earshot of your bedroom window. (Colorado spruce and white spruce grow quite rapidly; Black Hills spruce are more compact and a little slower growing.)

Evergreens also form an excellent backdrop to a deep perennial bed. Their dark green provides a perfect foil to the brighter flower colors; they can also offer some shelter from prevailing winds and help trap snow in winter.

Be sure to determine the growth potential of evergreens before you buy them. Watch out not to plant evergreens that grow tall and dense too close to your home.

Sheared shrubs=high maintenance. Photo credit: Beth Jarvis

It's not unusual to see the front of an otherwise attractive older home practically obscured by enormous evergreens that were probably only two feet tall when they were planted. These huge trees not only keep out light, they may present a significant security risk to the home and it's occupants.

Consider, also, removing any evergreen foundation plantings that have outgrown their usefulness. It's not a crime to replace healthy arborvitae, yews or junipers that are growing up into the eaves of your house or sprawling out over your sidewalk, making it virtually impassable.

These are fast-growing shrubs. When you put in smaller versions of the same plants, they'll grow to the size you want within a few years. Prune them annually, once or twice in late spring and early summer, to keep them from growing out of bounds again so rapidly.

If you want to plant or replace evergreens in your landscape, now is the perfect time to visit your local nursery or garden center. There are many advantages to planting evergreens in fall. New, tender growth that developed in May and June is tougher by now, and less vulnerable to transplant stress. Longer, cooler nights and slowly declining daytime temperatures mean reduced moisture loss through their needles. This, in turn, creates less demand on the plants' limited root systems. And, there's usually ample rainfall in autumn.

Another advantage you shouldn't overlook: most nurseries offer a fine selection of trees and shrubs -- including evergreens -- at discounted prices this time of year. They prefer selling at a reduced price to carrying the plants over winter.

Mulched arborvitae. Photo credit: Jim Calkins

By mulching newly transplanted evergreens with three or four inches of shredded bark or wood chips you can extend the time before soil freezes. Spread the mulch over the root area as far as the branches reach or further, but don't mulch directly against the trunk. Leave a little space surrounding it to promote good air circulation.

While watering is certainly important, the combination of cooler temperatures and more frequent rains should reduce your need to water regularly in autumn. Any time we go a week without good rainfall, however, give the root ball and area around it a thorough soaking.... right up until the time the ground freezes. Because evergreens continue to lose moisture through their needles year-round, it's doubly important you don't allow them to go into winter stressed for moisture.

Extension folder 1430, Choosing Landscape Evergreens, suggests the following evergreens for problem sites in the landscape:

Clay soil:	arborvitae, Austrian pine, ponderosa pine, white fir, Colorado spruce
Sandy soil:	jack pine, mugo pine, Norway pine, scotch pine, junipers
Wet Soil:	American arborvitae, balsam fir, black spruce
Partial Sun:	arborvitae, balsam fir, douglas fir
Shade:	Canada hemlock, Canada yew, Japanese yew
Exposed, sunny site:	Black Hills spruce, jack pine, mugo pine, ponderosa pine, Rocky Mountain junipers, Eastern red cedar
High pH (alkaline soil):	arborvitae, Black Hills spruce, Colorado spruce, mugo pine, ponderosa pine, junipers

Fall, An Excellent Time To Control Those Persistent Perennial Weeds
Roger Becker, Extension Agronomist-Weed Science

Dandelions. Photo credit: Beth Jarvis

Why Now?
Fall provides an excellent opportunity to control perennial weeds such as common dandelion or creeping Charlie. In the fall, perennial weeds translocate (move) the sugars produced in leaves to underground roots or rhizomes for the winter and to fuel next year's growth. This downward movement of sugars really kicks in the first two weeks of September in the southern half of Minnesota. In the northern half of the state, this activity peaks the last week of August through the first week of September. It continues as long as the plants are not killed by frost and 50 to 75% of their leaves are still green and actively growing.

Herbicides that are systemic (translocate within the plant) move very effectively with these plant sugars to the roots in the fall. Fall herbicide applications are generally more successful in killing weeds, roots and all, than either spring or summer applications.

Spring or summer applications of herbicides may damage the emerged leaves and sufficiently control the underground portions. During this time, plants are moving sugars up from the underground storage parts to produce new shoots. Herbicides do not move against this flow very well.

This upward movement of sugar continues until after flowering. Consequently, considerably less herbicide gets to the underground portions if applied in the spring or summer than the same amount applied in the fall. Without destroying the root system, perennial plants may still be able to regenerate.

These systemic herbicides are applied post-emergence, after vegetation has emerged. With most post-emergence herbicides, very little herbicide moves into the plant through root uptake from the soil.

Creeping Charlie. Photo credit: U of M Extension Svc.

Contact herbicides burn leaves that are sprayed but do not move to the roots so they do not control underground parts of perennial weeds. Contact herbicides such as those containing glufosinate (sold as Finale) may be used to burn off emerged vegetation in driveways, patios, sidewalks. Some of the organic nonselective sprays containing potassium salts of fatty acids can be used similarly. Repeated applications will be needed on perennial plants during the growing season.

Annual weeds like crab grass germinate from seed, flower and produce seed before winter kills the plant. They must start from a seed every year, and do not establish well in a competitive turf. Once the turf is well established, annual weeds should not persist unless disturbances occur to open up the canopy. Diseases, winter kill, vole damage, or drought are examples of disturbances. Annual weed problems in established turf indicate that management may need to be improved. Systemic or contact herbicides work well on annual weeds but will not kill seeds.

(Ed. Note: Control of crabgrass and other annual weeds will be discussed next spring.)

Biennial plants require two years to complete their life cycle. They store food reserves in leaves and roots the first year, and require a winter to flower, then produce seed the second year. Biennials must start from seed to begin this two-year cycle, and like annual weeds, do not establish well in competitive, well maintained turf. An occasional thistle like musk thistle can appear in lawns.

Once established, perennial turf weeds live for more than two years, with new shoots emerging in the spring from underground roots or rhizomes that survive the winter. Perennials such as common dandelions produce abundant seed, and may be present as a seedling behaving like an annual the first year. These seedling perennial weeds are relatively easy to control with herbicides.

Common turf weeds:

Perennials (Best controlled in the fall)
Broadleaves:
Plantain (several)	Mouseear chickweed	White clover
Canada thistle	Common dandelion	Oxalis
Creeping Charlie
Grasses
Quackgrass

Biennials
Plumeless thistle	Musk thistle

Annuals (best controlled in the spring or early summer before flowering occurs)
Broadleaves
Common chickweed	Prostrate knotweed	Black medic
Spotted spurge	Prostrate spurge
Grasses*
Barnyardgrass	Large and small crabgrass	Foxtail species
*Best controlled in early spring with a pre-emergence herbicide

Preventing Weeds

Plantain in thin turf. Photo credit: Beth Jarvis

There is no substitute for good turf management to control weeds. Proper management to prevent weed establishment includes appropriate fertilizer application, watering, mowing frequency and height, and adapted turf species. Proper management improves the competitiveness of desirable turfgrass and prevents weeds from establishing or if established, minimizes their spread. Mowing can be an effective cultural practice to control annual and biennial weeds by reducing seed production, but weeds often adapt and grow low to the ground under repeated mowing and still set seed.

If significant weed problems develop or persist, herbicide use may be necessary. As we discussed in the beginning of this article, now is the ideal time to control perennial weeds with systemic herbicides. Fall herbicide applications not only control established perennial plants, but have the additional bonus of controlling perennial seedlings that may have emerged this summer.

What to Use??
The broadleaf perennial weeds such as common dandelion are very susceptible this time of year to herbicides containing 2,4-D or mixtures with 2,4-D. Creeping Charlie and violets can be controlled with herbicides containing triclopyr. (Products containing triclopyr and labeled for broadleaf weed control may not be available in consumer sizes. You may need to hire a lawn care company to spray the lawn.)

Quackgrass is effectively controlled with herbicides containing glyphosate (eg: Round Up, Kleen Up, etc.) in the fall to renovate turf or to cleanup non-turf areas. Remember, glyphosate based herbicides are not selective so do not apply to desirable plants.

For information on particular weeds and control methods, click on:
Yard & Garden Briefs for information sheets on individual weeds.
Weed Control in Lawns and Other Turf

Controlling Wasp Nests
Jeffrey Hahn, Assistant Extension Entomologist

Yellowjackets nesting in tree cavity. Photo credit: Jeff Hahn

Wasps continue to be an important problem. Because of our early spring, their numbers are higher than normal. If you have a wasp nest that needs to be controlled, take care of it as soon as possible. In cases where wasps are living in places away from people, e.g. in the tops of large trees or in exposed sites high up on buildings, they are less likely to encounter people and it is not as important to eliminate these nests.

However, you should control nests that are near human traffic to reduce the chance of stings. When you find wasps nesting in the ground, first try pouring a sudsy soap and water solution into the entrance. If that doesn't work, sprinkle a dust, such as permethrin, into the opening or mix a liquid concentrate, such as acephate (Orthene), with water and pour it down the nest entrance. Plug the hole with dirt after all the wasps have been killed.

You can deal with nests hanging in exposed sites, such as in trees or on buildings, by spraying an insecticide labeled for wasps and hornets into the nest opening. Do this during late evening when the wasps are less active. If there are still wasps that are alive after a few days, repeat the spray.

The most challenging type of nest to eliminate are those that are concealed in voids behind walls or in attics. You don't actually see the nest, but you see where wasps fly back and forth through a crack or hole. As long as wasps are alive, do not plug that entrance. If the opening is sealed, wasps look for another way out and often end up inside the home. If the nest is not near the entrance, an aerosol insecticide sprayed into the opening will not work very well to control the colony. Instead, apply a small amount of insecticidal dust (such as bendiocarb, deltamethrin, or boric acid) through small holes (you will probably have to drill these holes). This may be a pest problem best handled by a reliable pest control service.

Some people choose to do nothing and just ignore nests in wall voids. The advantage is that wasps end up going away on their own without having to control them. However the risk is that even if you do nothing to annoy them, wasps may still invade your home as temperatures cool. Its a bit of gamble deciding what to do.

No matter what you do with any type of wasp nest, all wasps die by fall when we receive hard frosts. Only new queens, that have already left the nest and overwinter elsewhere, survive.

Aphids on Black-eyed Susan (Rudbeckia)
Jeffrey Hahn, Assistant Extension Entomologist

Aphids on black-eyed Susan. Photo: Jeff Hahn

Flowers often tolerate aphid feeding without any visible signs of injury.

However, this summer, reddish aphids (probably Macrosiphum sp.) have been common on some black-eyed Susan (Rudbeckia). Rudbeckia hirta, the common prairie species seems to be most susceptible to infestations.

Large aphid numbers cause discoloration of flower petals and leaves and result in general wilting. If you wish to control them, consider applying insecticidal soap to reduce aphid populations. This product is effective against aphids but has little effect on natural enemies, like ladybird beetles. However, this isn't necessary as even a severe infestation is not likely to kill the plant.

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

Aster Leafhoppers
Jeffrey Hahn, Assistant Extension Entomologist

Aster leafhopper nymph. Photo credit: Bill Hutchison

Aster yellows has been a conspicuous problem in home gardens this year particularly on purple coneflowers (see YGL June 15, 2000). This disease is vectored by the aster leafhopper, Macrosteles quadrilineatus. The following aster leafhopper biology is modified from a fact sheet written by Bill Hutchison. To view the original publication, go to Bill's VedgeEdge website: http://www.vegedge.umn.edu/vegpest/colecrop/aster.htm

The major source of aster leafhoppers in Minnesota is the spring migration of adults from the southern United States. Migration of aster leafhopper occurs via transport on northern jet streams. Several weeks after their arrival, a small number of aster leafhoppers hatch from overwintering eggs found in winter wheat or other grass species. Five nymphal stages are completed in about 2 weeks.

Important vegetables that serve as hosts include lettuce, celery, carrots, endice, and parsnip. During early to mid summer, as winter grasses senesce, newly emerged adult aster leafhoppers move to these crops, as well as more succulent spring grain, weed hosts, and susceptible vegetable, ornamental and field crops. Common weed hosts for aster yellows include: thistle, fleabane, wild lettuce, sow thistle, chicory, wild carrot, galinsoga, dandelion, plantain, cinquefoil and others. Susceptible flowers include aster, chrysanthemum, cockscomb, coreopsis, cosmos, daisy, dianthus, echinacea (coneflower), gladiolus, marigold, petunia, and phlox. Overall, 150 species of plants in 40 different families have been recorded as hosts of aster yellows vectored by the aster leafhopper.

Adult aster leafhopper. Photo credit: Bill Hutchison

To acquire and transmit the aster yellows mycoplasma, the aster leafhopper must feed for a prolonged period (at least two hours) on an infected host (either locally or in a southern state). Next, the pathogen must incubate within the leafhopper for about 3 weeks before it can be transmitted to another plant. Because of the extensive incubation period, the disease is rarely spread from plant to plant within a commercial field. Thus, the primary method for transmission of aster yellows to a host in Minnesota is by the migrant adults already carrying the pathogen.

Management in home gardens includes promptly destroying and discarding diseased plants to prevent further spread. Also remove weeds because they may act as reservoirs for the microorganism. Chemical sprays to control the leafhoppers in home gardens are not practical and are not recommended.

You can attempt to protect your garden plants by placing oat straw mulch or aluminum mulch around your plants. Oat straw is probably difficult to find for most people. If you decide to use aluminum you can use ordinary foil cut into strips. The idea for this is to have something that is light in color. Aster leafhoppers use UV light to help orient themselves to fly up when they first take off. They then look for green and dark surfaces to land. When they encounter a garden with light-colored mulch, the UV light repels and confuses them so they literally don't know if they coming or going.

The highest incidence of aster yellows occurs in the spring when aster leafhoppers first arrive in May so have mulch in place by then. Add new mulch as the old material ages and becomes darker (dark mulch is less effective in repelling leafhoppers). Using mulch is not a cure-all but it can help reduce the incidence of leafhoppers in the garden.

Black Willow Aphids
Jeffrey Hahn, Assistant Extension Entomologist

Weeping willow. Photo credit: Beth Jarvis

Black aphids with orangish or brownish legs and cornicles (the tail pipes of an aphid) on willow are black willow aphids. They are large for an aphid, reaching up to 3/16th inch in length. They can be quite abundant in August and September. These aphids are common on willows and may also be found occasionally on poplars and silver maples.

Black willow aphids secrete honeydew, a sticky sugary substance which will coat any object underneath an infestation. Yellowjackets may be attracted to infested trees because of the honeydew. In addition to being a problem in trees, these aphids sometimes have an annoying habit of dropping to the ground and collecting around buildings and nearby objects. If their bodies are crushed, they can stain siding and other objects a blue-purple color.

Despite their abundance, they do little if any lasting harm to established, vigorously growing trees. Their presence is just a nuisance. Tolerate these aphids as much as possible. If you wish to reduce their numbers, try washing them off as many branches as you can reach with a hard spray of water. A less toxic insecticide option would be treat them with insecticidal soap. If nothing is done, their numbers will diminish on their own by the end of the month.

Tortoise Beetles in Gardens
Jeffrey Hahn, Assistant Extension Entomologist

Plagiometriona clavata feeding on Chinese lantern Photo: Y & GL

Tortoise beetles are small (about 1/4 inch long), round, turtle-like insects. They have thin margins that extend out from their body as well as a shield-like structure that covers their head. Tortoise beetles vary in color, some are dark while others have bright metallic colors. Tortoise beetles are one of the few insects that can change their metallic colors. Their larvae are interesting because they glue caste skins, debris, and excrement together and hold it over their back like an umbrella. They stick this material at potential predators to protect themselves.

Tortoise beetles are a type of leaf beetle and feed on the foliage of various plants. Although their can feeding can be potentially severe, they are seldom reported as a problem in gardens here in Minnesota. The tortoise beetle, Plagiometriona clavata has been reported recently on Chinese lantern. It is also reported in the literature to feed on jimson weed, Datura stramonium and (presumably) other members of the Solanaceae. They chew round holes in the leaves, although submitted samples showed only minor to moderate damage. There have been other reports of tortoise beetles this summer on various garden plants. Different species are known to feed on plants in the morning glory family (Convolvulaceae).

For the most, this damage is not important, especially this late in the summer. Tortoise beetles damage is rare in Minnesota gardens. If it's necessary, hand pick small number of these beetles. If large numbers are present and control is desired, use a residual insecticide (e.g. permethrin, acephate, carbaryl)

Editorial Notes

Clematis seedheads. Photo credit: Beth Jarvis

It's hard to believe it's September already! Labor Day weekend is a great time to be out doing those lawn care chores. I hope you found Roger Becker's piece on fall herbicides inspiring and informative. Next spring, he'll write about how to keep annual weeds from coming up at all. Later, he'll write about how various common herbicides work.

Some time soon, I'll have a piece by Terri Port, from Duluth about a shoreline restoration project she worked on. Oct. 1, Jon Powell, turf pathologist, will return discuss fall and lawn diseases.

In future issues:
*An update on the apple bagging project, a non-chemical apple production method for homeowners.
*Soluble salts on soil tests--what's mean?
*Growing grapes in Mn.
*Conservation biocontrol--what is it?
*Does treated lumber leach arsenic?

I rely on your comments and questions for ideas for future articles. Please, keep the story ideas coming! We really try to be responsive to your needs.

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
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Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator

Websites
Sustainable Urban Landscape Information Series. This site contains everything from landscape design planning and lawncare to both herbaceous and woody plant selection databases. The URL is:http://www.sustland.umn.edu


For pesticide info, for both home owner and professionals, check out:

http://www.crc.agri.umn.edu/~mnhelps/

There's also some very interesting reading at Forest Products website. To get there from here, click on: http://www.cnr.umn.edu/FR/extension/
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