Yard & Garden Line News
Volume 1 Number 9                                                               August 15, 1999
Features this issue:
 Focus on: the Soil Testing Lab
Growing Ground Covers
Crabgrass, Foxtail & Barnyard Grass
Order Spring-Flowering Bulbs to Plant This Fall
Keep Weeding Your Garden
Minnesota Apple Season is Here!
Yellowjacket Nests
Insect Damage to Apples
Fall Webworms
Spiders at the End of Summer
Foliar Diseases of Tomato
White Mold
Oak Wilt
The Development of New Garden Chrysanthemums
Editorial Notes

Focus on: the Soil Testing Lab!
Roger D. Eliason, Laboratory Manager, Soil Testing Laboratory

Removing a portion of 
prepared sample for testing.
Som Lekhakul
performs the Bray test for phosphorus.
pH Running the lime requirement test for acidic soils is done by Ruby Adams.
Samples drying. Samples need to dry before analysis.
K test Agnes Fulop analyses soil extract for potassium.
Photos: Soil Testing Lab
Why soil sample?
Fertilizers are a modern miracle and have revolutionized the plant growth industry. However, fertilizer in the wrong place can create water quality problems for our aquifers, lakes and streams. In our "Land of 10,000 Lakes", we want to enjoy the benefits and beauty of well-grown plants, without the negative consequences of water pollution. A soil test is a great way to start! With a soil test, we can apply only the fertilizer that is needed to nourish a healthy plant and avoid any unnecessary excess fertilizer that could become a pollutant.

What is the Soil Testing Laboratory at the University of Minnesota?
The University of Minnesota Soil Testing Laboratory is a service that provides soil analysis and fertilizer recommendations for farmers, nurseries, florists, turf managers, homeowners and gardeners. We analyze between 10,000-15,000 samples each year and support ourselves from the fees that we collect from our customers.

How do I get a Soil Testing Kit?
A kit can be obtained directly from the Soil Testing Laboratory at 612-625-3101 or from your local County Extension Office. The laboratory can also be reached from the Yard and Garden Line at (612) 624-4771. Select #4 from the main voice mail menu.

The kit contains an information sheet describing how to take a sample, the cost of analysis and where to send the sample. The kit will also contain two soil sample bags that you can use to transport the sample.

What will the test tell me (and not tell me)?
The tests provided by the Soil Testing Laboratory are for the purpose of evaluating the soil fertility and soil pH level (regular test), and/or problems due to excessive salts or fertilizer materials (soluble salt test). Based on these test results and the type of plants to be grown, you will be sent the appropriate fertilizer recommendations. Problems with plants may be caused by factors other than soil fertility, such as disease, insects, insufficient light, soil moisture or compaction, or climatic conditions. If soil fertility is not found to be a problem, then the other factors affecting plant growth should be evaluated to determine possible causes.

What is the regular series test?
A regular series test provides the customer with a test for phosphorus, potassium, pH, lime requirement (if necessary), organic matter, and texture estimate. The phosphorus and potassium tests give an index of the amount of nutrient that the soil can supply to the plants. With this information, it is possible to make fertilizer recommendations that will allow one to supplement the soil nutrient pool and avoid deficiencies of those nutrients. The soil pH will indicate whether the soil is acid or alkaline. For most situations, a slightly acid condition (pH=6-7) is best. If the pH is too acid, then the lime requirement test will indicate the amount of lime necessary to raise the pH to the optimum level. Fertilizer and lime recommendations are provided on the report mailed to the customer.

What about nitrogen?
A test for nitrogen is not conducted with the regular test. This does not mean that nitrogen is not important, but rather that we do not have a test available for nitrogen that can accurately predict the amount that the soil can supply over the course of the year. Nitrogen is mobile in soils and changes forms easily depending on the conditions. Thus any nitrogen form that is measured today may have changed to another form by next week.
As a result, the nitrogen recommendation is not based on a specific test. Rather, the nitrogen recommendation is often based on a number of factors including the organic matter level of the soil, the previous crop grown on the site, the amount of watering, and the removal of clippings.

How long does it take for an analysis?
Sometimes people think that with all the advancements in science, analysis can be completed in a matter of minutes. The fact is, in soil testing the sample requires special handling and preparation for proper analysis. This includes low temperature drying (95° F) and crushing and sieving of the sample. Proper sample handling provides for accurate results, which will mean better fertilizer recommendations for the plants. In general, a relatively dry sample arriving in the laboratory on Monday morning, will be prepared in the afternoon, dried overnight, analyzed on Tuesday, and a report mailed to the customer on Wednesday. Wet samples or special tests can extend this time by a day of two.

When do I take a soil sample?
You can take a soil sample at any time of year. However, the prime seasons are in the spring and fall. Fall is an especially good time to fertilize your lawn. At this time, the grass plants are producing energy to store for the winter season and much of the new growth will go into establishing a healthy root system. A lawn fertilized in the fall will stay green longer in the fall, green up faster in the spring, have higher energy reserves, and be less prone to disease the next season. Fall is also an excellent time to re-seed any bare spots or to establish a new or renovated lawn. A soil test can get your fertilizer program off to a good start with the proper level and application schedule.

How deep should the sample be?
The depth of the sample depends on the type of plants to be grown. In general, you want to take the sample from the slice of soil where the roots will be feeding. For established lawns this is 0-3", for gardens 0-6", for trees or shrubs 0-12". For new turf situations sample to a 0-6" depth because the P and K fertilizer will be worked into that depth of soil when the site is prepared.

What kind of fertilizer do I buy?
The soil test report will give a suggested ratio of nutrients that would be ideal for your soil. If you can match this ratio, that is great! However, sometimes this is not possible because a fertilizer with the exact ratio that you need is not available. This is particularly true of situations where phosphorus fertilizer is not recommended. Many stores do not carry a phosphorus free fertilizer. If you can not find a fertilizer that exactly matches the recommended ratio, it is best to buy a fertilizer that is as close as possible to the recommended ratio. Then apply the fertilizer at a rate that will supply the nitrogen needs called for in the soil test report. A chart and instructions are found on the backside of the Lawn and Garden report to help with this calculation.


Growing Ground Covers
Deborah Brown, Extension Horticulturist

snow on the mountain Snow on the mountain.
Photo credit: Deb Brown
Professor Don White, turf specialist at the University of Minnesota's St. Paul campus, considers Kentucky bluegrass not only the best, but the most easily maintained "ground cover" you can grow here. None-the-less, the use of non-grass ground covers is on the increase as people become more aware of how ground covers can perform in the landscape, and learn of the wide diversity of choices available to them. So if you're tired of mowing, give some thought to converting some of your yard to ground covers.

Why Use Ground Covers?
You can look at ground covers from two distinctly different perspectives. First is to consider using ground covers as a way of dealing with difficult landscape problems, creating labor-saving alternatives to growing or mowing the lawn.

For example, ground covers can eliminate having to deal with the safety hazards and pure drudgery of cutting grass on a steep hill. And many ground covers thrive in shady areas where lawns will never grow well. You can also plant them in small "remnant" areas that aren't large enough for gardens, yet would be a real pain to keep in grass.

The second way to think about ground covers is to consider their aesthetic attributes and the positive ways they may contribute to your landscape. They can add color, form, texture, and sometimes even fragrance to your landscape.... regardless of whether you have a specific maintenance problem to grapple with.

Creeping phlox, Phlox subulata, provides a two week burst of brilliant color when it blooms each spring, then stays green the rest of the growing season. Several cultivars of bugleweed, Ajuga reptans, have purple or metallic bronze-colored foliage, and common bishop's weed (also called goutweed or snow-on-the-mountain), Aegopodium podograria, adds a cooling touch with its soft white and green variegations. Lady's mantle, Alchemilla mollis, produces clusters of diminutive lime-colored blossoms held above its large, grass green leaves.

ajuga Ajuga
Photo credit: Beth Jarvis
Ground covers come in many forms and sizes, from soil huggers to three or four foot tall daylilies and suckering woody shrubs like sumac or bush honeysuckle (Diervilla lonicera.) Ferns appear delicate and lacy, while European ginger, (Asarum canadense) and fleeceflower, Polygonum cuspidatum compactum, are more coarsely textured. Large-leaved hostas are coarser, yet. Depending on location, each may have a role to play in a well-designed landscape.

How They Grow
It's obvious that to function well as a ground cover, plants must spread and cover the ground efficiently so weeds don't move into the area and so their roots can help stabilize the soil. The more aggressively they spread, the sooner the soil will be covered and better their roots will protect slopes and banks against erosion.

The downside of this aggressive spreading is that good ground covers don't always know enough to stay within the bounds you assign them. Creeping charlie is a "worst scenario" example of how a cultivated, introduced ground cover has run amok, causing nightmares -- and the wrath of neighbors -- when it's not controlled.

Most ground covers are more mannerly than creeping charlie, but not all. A few -- wild violets, bishop's weed (also called goutweed), fleeceflower, vigorous old-fashioned tawny daylilies, lilies-of-the-valley, and some ferns -- are commonly grown ground covers known to move out of their beds and into the lawn.

Clearly, not all ground covers are "problem spreaders." Individual hosta plants grow larger, and cover more territory each year, but they don't send out runners that result in new plants growing quite a way out from the original, nor do they produce sprawling stems that root down. The same is true for newer daylily cultivars. They may increase enough in size to warrant dividing every three or four years, but they don't spread the way the older "ditch lilies" do.

daylilies Tawny daylilies.
Photo credit: Beth Jarvis
Even aggressively spreading plants pose no problem when they're surrounded by sidewalks, driveways, buildings and walls. For others, metal plastic or brick edging is all that's needed to keep them in their place. It's only when they're allowed to "bleed" out into the lawn that people begin to question the wisdom of planting them in the first place.

The message? When choosing ground covers, make sure you're picking the best plants for your specific site. That means you need to take into consideration not only the amount of sun, shade and moisture they'll receive and the soil type where they'll be planted, but how much effort may possibly be needed to contain them.

Planting Ground Covers
The best time to plant ground covers is in spring, when soil is moist and temperatures are still cool. You could plant them now, but time is running out for them to become established in their new location before the ground freezes. (If you do plant in fall, be sure to mulch the ground covers for added winter protection.)

Before you plant any ground cover, it's important to clear the area of all weeds. They'll compete with the young plants for moisture and nutrients. Pay special attention to tenacious perennial weeds such as creeping charlie or quackgrass.

It's not a bad idea to concentrate on eliminating weeds this fall in anticipation of planting next spring. Once ground covers are in place it will be practically impossible to use any herbicide, and tedious to weed manually. Eventually, as they do their thing, your ground covers should shade out most weed seeds, relegating weed control to the status of a minor maintenance item.

Lady's mantle Lady's mantle.
Photo credit: Beth Jarvis
It's also a good idea to have your soil tested before planting. (It only takes a week or so to get results back from the U's Soil Testing Lb.) Then you can add recommended nutrients along with two or three inches of organic matter such as peat or compost when you rototill or turn the soil over prior to planting.

The final step before digging holes for your plants is spreading an organic mulch over the soil surface. Mulch will help conserve soil moisture by reducing surface evaporation and will also help insulate plant roots from fluctuating temperatures. As organic mulch decomposes it adds humus and, ultimately, some nutrients to the soil.

Bark chips, shredded bark or corn stalks, pecan or almond shells are among the many organic materials that work well for mulching. Be sure not to lay plastic or landscape fabric beneath the mulch, however. They would interfere with your ground cover's ability to push up new plants at the ends of underground runners, and would also prevent horizontal stems from rooting down into the soil.

Maintaining Ground Covers
Water young plants thoroughly once they're in the ground, then continue to water regularly until they've become established. After that, water them only when they show signs of needing the moisture. Thorough watering is always preferred to shallow sprinkling because it encourages plants to develop deep roots that will help them get through dry periods later on.

Ground covers are not totally maintenance free, they just don't require intensive maintenance. Once they're established you'll need to fertilize each spring, water periodically, and keep on top of any weeds that show up. Some plants will have to be cut down first thing each spring, or in fall after their foliage has been frost-damaged. But when you think of all they add to the landscape, it's not a large price to pay.

wild ginger Wild ginger.
Photo credit: Beth Jarvis
To Learn More About Ground Covers:
The best, most comprehensive book on ground covers suited to this area is Ground Covers for the Midwest by Voight, Hamilton and Giles. It is a large, clearly written regional Extension publication, illustrated with line drawings and several pages of color photographs. You can order this book ($14) by calling the Yard & Garden Line toll free at (612) 624-4771. Select "2" for publications, then "3" for Distribution Center. Ask for BU-5777.

There is also a one page Minnesota fact sheet, Covers for Rough Sites, FS-1114, that focuses specifically on ground cover choices for problem areas.

Crabgrass, Foxtail & Barnyard Grass
Deborah Brown, Extension Horticulturist

foxtail Foxtail
barnyardgrass Barnyardgrass.
Photo credits: Dowelanco
Many people are plagued with huge patches of annual, grassy weeds in their lawns; weeds such as crabgrass, foxtail and barnyard grass. These weeds started to become obvious in mid-July, and will continue to thrive until they eventually succumb to freezing temperatures. Though plants die over winter, they leave a legacy of seeds on the ground that will remain viable for years.

There's no point in spraying them with "crabicide" or post-emergent herbicide once they're big and tough. The only time these products are very effective is when the weeds are still young and tender... at the two to three leaf stage. By the time they're real apparent in the lawn, it's too late.

Instead, apply a pre-emergent herbicide in early May. This should prevent seeds from sprouting next year provided you get good coverage and you water the product into the soil, then leave the soil undisturbed.

To reseed these weedy areas this fall, mow the weeds close to the ground, then use a dethatching rake or rent a power rake to remove as many of them as possible. Seed in late August or early September. Grass seed planted in fall should come through the winter thicker and stronger than before, and you can use a standard pre-emergent herbicide on it next May.


Order Spring-Flowering Bulbs to Plant This Fall
Deborah Brown, Extension Horticulturist

spring bulbs Spring bulbs
Photo credit: Netherlands Flower Bulb Assn.
In the midst of enjoying summer lilies, phlox, dahlias and daisies, it's probably unlikely that you're thinking much about tulips and daffodils. But whether you plan to order bulbs from Holland or a mail-order nursery in the US, now's the time to figure out what you need. If you wait too long, you may not get the varieties you prefer. Worse yet, they may come too late to be of much value.

Choose the largest size bulbs available; they'll produce bigger flowers and will be more likely to bloom for several years before they have to be replaced. Order enough of each variety to plant a cluster of identical flowers; you'll get much more visual impact than stringing them out in a row.

Early and mid-season tulips usually work best in Minnesota. By the time late season varieties bloom, our weather can be hot enough to significantly shorten the bloom time for each blossom. They may open one day, then be past their prime the next.

Watch out for large collections of bulbs. Sometimes they include plants that aren't reliably hardy here. For example, Dutch iris (from bulbs) can't take our winters and the delicate little Iris reticulata is extremely marginal. Showy anemones (Anemone 'de Caen') and freesias are also poor choices for Minnesota gardens.

Keep Weeding Your Garden
Deborah Brown, Extension Horticulturist

sq. ft. gardening Closely planted vegetables crowd out weeds.
Photo credit: Deb Brown
Even though weeding the garden can get pretty tiresome by late summer or early autumn, don't give up. Along with competing for moisture and nutrients, weeds can harbor insects that carry diseases from plant to plant. And, of course, they bloom and set seeds that will come back to haunt you next year and for years to come.

Many weeds can be pulled easily out of garden soil after you've watered it. Others can be sliced off with a sharp flat hoe. If quackgrass is encroaching on your garden, though, you might be better off spot killing it by wiping individual plants with a sponge that's been dipped in glyphosate (Round Up).

Wear good rubber gloves or attach the sponge to a long handle (such as a ruler) so you don't come in direct contact with the herbicide. Use the weed-killer only on green, growing weeds. Once they yellow, the herbicide won't be taken in. As long as you don't touch parts of your flowering plants or vegetables, they will be unharmed by your use of the herbicide.

If you aren't presently using mulch in the garden, remember to put some down next spring. Even a simple mulch such as two to three inches of grass clippings will help in suppressing annual weeds.

Minnesota Apple Season is Here!
Doug Foulk, Extension Educator, Ramsey County
Oriole 'Oriole" apples.
Photo credit: Dave Hanson, U of M Extension  Service
Although most people think of apples as a fall crop, several cultivated varieties (or 'cultivars') ripen in late summer, as early as the first week in August in some years. These early apples are a great kick-off to our annual apple season.

The first cultivars to ripen in Minnesota are 'Mantet,' 'Oriole' and 'Duchess.' 'Mantet' and 'Oriole' are both suitable for fresh eating, pie and sauce, while 'Duchess,' due to its tart flavor, is generally considered a pie and sauce apple only. 'Oriole' (figure 1) is an attractive and aromatic apple that makes a flavorful, albeit soft, pie filling that rivals the taste of later apples.

Other extra-early apples you may find offered in Minnesota orchards include 'Julyred,' 'Viking' and 'Lodi.' Always purchase small quantities of the extra-early cultivars as they keep for only about a week, even under the best of storage conditions.

sta fair 'State Fair' apples.
Photo credit: Dave Hanson, U of M Extension Service
By mid-to-late August 'State Fair,' 'Paulared' and 'Beacon' all become available. These cultivars are easier to find than the earliest August types and last somewhat longer in storage. 'State Fair' (figure 2) in particular is a standout. Juicy and aromatic, with an old-fashioned apple flavor, 'State Fair' is equally at home baked in a pie or fresh in your hand. 'State Fair,' 'Paulared' and 'Beacon' will store for two or three weeks loosely covered in your refrigerator.

Should you grow these early apples in your home garden? Because they ripen so early, you may find that they require fewer pesticide sprays than later cultivars. However, because they do not store well, you may find it difficult to use all the apples you produce. For home production, grow an early apple cultivar on a dwarfing rootstock, such as M26 or Bud 9. Remember that you need at least two different apple cultivars within 100 feet of each other to produce fruit. However, the two cultivars do not need to ripen at the same time of year for pollination to occur, and in fact, even a flowering crab works just fine.

Of course, the best time to plant an apple tree is in early spring. Now, however, is your chance to research available cultivars and decide which ones to grow in your own yard. With August apples like 'Oriole' and 'State Fair' here now and September apples like 'Chestnut Crab' and 'Honeycrisp' on the way, you'll want to be doing a great deal of research!

Yellowjacket Nests
Jeffrey D. Hahn, Assistant Extension Entomologist

hornet nest
Bald-faced hornet nest in winter.
hornets Yellowjackets' nest in building. Photos: Jeff Hahn
Yellowjacket populations are not as numerous as they were a year ago, but they still can be quite bothersome at the end of summer. When dealing with colonies around homes, you can ignore nests that are up high in trees or buildings or otherwise not close to where people spend much time. However when yellowjackets are nesting close enough that there is a risk of stings, then they should be eradicated.

Nests that are out in the open are fairly easy to deal with. Wait until evening when the yellowjackets are less active and treat the entrance to the nest with an aerosol insecticide. Just spray directly into the opening where yellowjackets have been flying back and forth. Choose a product that is registered for 'wasp and bee' control. Check the nest the next day for activity. If after a few days there are still live yellowjackets, repeat the treatment.

If you find a yellowjacket nest in the ground, you can control it by pouring soapy water into the nest entrance. If you wish to try an insecticide, try one of the following: carbaryl (Sevin), diazinon, acephate (Orthene) as a dust or liquid. Dusts are generally more effective than liquids.

The most challenging nest to deal with are those that are hidden in wall voids or other inaccessible areas. You won't see the nest but you will notice an opening where yellowjackets fly back and forth. Aerosol sprays are generally not effective because the nest is not necessarily near the opening. In fact an aerosol spray can irritate yellowjackets and cause them to enter the interior of a home. The same result can occur if you seal up the entrance; the yellowjackets will just look for another way out which often leads to the inside of your home.

The best method for eliminating yellowjacket nests in walls is to apply an insecticidal dust. Products containing either bendiocarb or chlorpyrifos (Dursban) are available to the public for use indoors, although they can be hard to come by. It probably is best in many cases to contact a experienced pest control service to dispatch those hard to reach nests.

Insect Damage to Apples
Jeffrey D. Hahn, Assistant Extension Entomologist
and
Jennifer Hinton, Entomology technician
apple damage
Insect feeding injury can distort fruit.
Photo credit:
Yard & Garden Line
As people are just starting to harvest apples, they are finding various types of injury due to insects. Two common apple pests whose injury is readily seen during harvest are plum curculio and codling moth.

Plum curculios overwinter as adults. In spring, they move to trees and lay eggs in apples, about the time trees are flowering. As the female weevils oviposit, they leave a crescent-shaped scar on the apple. Severely attacked apples can also become deformed. Larvae feed for about two weeks. Larvae exit from fallen apples and pupate in the soil. They emerge later in the summer and then hibernate. There is just one generation per year.

Codling moths overwinter as mature larvae. Moths start to appear in spring as the last petals fall from the apple blossom. Female moths lay eggs on fruit or nearby leaves, which hatch in 6 to 14 days, depending on temperature. Codling moths can damage apples in two ways. By burrowing through the apple into the core, either from the side or from the calyx end or by causing stings, i.e. where larvae started feeding but then stopped. After feeding for about three weeks, full grown larvae exit the fruit in late July and pupate on the trunk or larger branches of the tree. A second generation can occur starting in late July or August.

The best time to treat both of these insects is in the spring. Two applications are made, one at petal fall, i.e. when about 3/4 of the petals have fallen and a second application about ten days after the first treatment to maximize management. Use one of the following insecticides: phosmet (Imidan), diazinon, or malathion + methoxychlor. It is too late to treat plum curculio now. Although codling moth is just starting a second generation but it is probably unnecessary to spray for them now.

Fall Webworm
Jeffrey D. Hahn, Assistant Extension Entomologist

fall webworms
Fall webworms webbing branch
Photo credit:
Jeff Hahn
These caterpillars have been active since the end of July but will continue to be conspicuous through the end of summer. These caterpillars feed on the leaves of over 100 different species of trees and shrubs. They are yellowish or greenish with long, fine white hairs with two rows of black spots down their backs.

Soon after they hatch, they produce a silken webbing, covering the ends of branches (or the entire tree or shrub if it is small). The webworms feed gregariously, i.e. as a nonsocial group, inside the webbing. This webbing can be large, as much as two to three feet across. When threatened, fall webworms will jerk their bodies simultaneously in an attempt to scare away any enemies.

Although common, fall webworm normally does not have much impact on the health of vigorously growing, well-established trees. Fall webworms are just an eyesore due to the webs they construct. Management is usually unnecessary because feeding at the end of summer has little impact on plant health. Also, natural enemies usually help keep fall webworms in check, preventing serious outbreaks. You can ignore fall webworms and not worry about serious injury.

If you are would like to improve the appearance of your plant, try pulling the webbing and caterpillars off the branches. Although it may be difficult to remove the entire web, you may be able to damage it enough to eliminate the fall webworms. You can also prune out branches containing webs as along as removal is not excessive or leaves the tree or shrub unsightly. Do not attempt to burn webs; this is more harmful to the tree than any control that is achieved.

Fall webworms are vulnerable to insecticides but only for a relatively short time when young larvae are first constructing webs. Bacillus thuringiensis, a bacterial insecticide, is a selective product that is effective against fall webworm but is a very low risk to people, pets, and nontarget insects. Once webs are larger, sprays do not penetrate through the webbing very well.

Spiders at the End of Summer
Jeffrey D. Hahn, Assistant Extension Entomologist

Black and yellow argiope spider.
Photo credit:
Jeff Hahn
Some spiders become quite conspicuous around homes as we near the end of summer. People may notice large spiders, such as black and yellow argiope spiders (at type of orb spider). These spiders make round webs several feed off the ground in tall grass, flowers and other plants. These spiders are sometimes referred to as garden spiders. Other large spiders that may be encountered are wolf and fishing spiders (both nonweb-builders).

Some people are tempted to think they have run into some exotic, dangerous spider (like the movie "Arachnophobia"). However, these spiders are actually common, even if people claim they have never seen them before. Despite their size, these spiders are not aggressive to people and are basically harmless. If you discover such a spider, just ignore it; you don't need to take any action against it.

It is also typical at this time to see increased numbers of spiders in and around homes as populations peak. This is particularly true for people that live in suburban and rural areas, especially near water. Spiders will be found where they can readily find food and aquatic areas provide an ample food source (from insects).

To control spiders, start outside. Clean up or move further away from homes brush piles, wood piles and other accumulations of materials that can be potential hiding areas for spiders. Also keep long grass and weeds near buildings cut down. The less conducive it is for spiders, the fewer there will be.

Check around the outside of the house and seal any obvious opening or spaces that may allow pests indoors. Knock down any spider webs that are found and crush any eggs sacs that are discovered.

In cases of high numbers, you can supplement these nonchemical efforts with an Insecticide application, such as permethrin, chlorpyrifos (Dursban) or diazinon. Spray especially into nooks and crannies where spiders may hide.

To control spiders inside, clean up areas where papers, boxes, and other objects have accumulated. Remove spider webs and crush eggs sacs that are found. Unwelcomed spiders can be easily killed with brooms or rolled up newspapers. You can use an aerosol insecticide (anything labeled for ants and roaches), as a supplement to your nonchemical efforts. Apply an insecticide around baseboards, corners and other areas where spiders are found.

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

Foliar Diseases of Tomato
Crystal Floyd, Plant Pathology technician

Septoria
Septoria leaf spot.
Photo credit:
Plant Disease Clinic
bacterial leaf spot
Bacterial leaf spot.
Photo credit:
Chad Behrendt
Late blight-leaves
Late blight on potato leaves
early blight
Early blight on potato
Photos: Plant Disease Clinic
Foliar diseases commonly occur on tomatoes in home gardens throughout the summer. Septoria, bacterial leaf spots, early blight, and late blight occur in Minnesota and may cause lesions on tomato leaves and fruit.

Septoria leaf spot, probably the most common leaf spot, usually occurs after fruit set. Numerous small, brown spots with tan centers develop on the lower leaves and progress upward on the plant. Leaves of severely affected plants may turn yellow and drop. Exposed fruit, due to defoliation, will be susceptible to sunscald. Septoria rarely infects the fruit.

Leaf spots caused by bacteria look similar to and are often confused with Septoria leaf spots. Bacterial leaf spots in contrast to Septoria leaf spots are generally smaller in size, uniformly dark colored, and surrounded by a yellow halo. Numerous spots can occur on leaves and green fruit.

The most distinguishing features of early blight are the leaf, stem, and fruit lesions. These lesions consist of concentric rings forming a target-like pattern. With early blight, there are typically fewer spots on each leaf than with Septoria or bacterial leaf spots. Heavily infected plants may defoliate and drop infected fruit.

Late blight differs from other foliar diseases in that it causes large, angular blotches. A white, fluffy growth may be present on the underside of the leaf below these blotches. Infected leaves shrivel and die. Fruit may become infected, displaying dark colored, greasy spots that may envelop the whole fruit.

Regardless of the foliar disease your tomatoes have this season, many cultural practices will help prevent or limit disease next year. Clean up and dispose of all plant material at the end of the season. Rotate crops and plant resistant varieties when available. Mulch and water around the base of plants to prevent dispersal of spores by water splash. Monitor plants for disease throughout the growing season. If disease is detected early enough, fungicides may be used to protect unaffected leaves and fruit.

White Mold
Chad Behrendt, Extension Plant Pathologist

white mold
White mold on salvia stem.
white mold/bean
White mold on bean stem.
Photos:
Plant Disease Clinic
White mold is a fairly common disease occurring on a variety of vegetables and ornamental plants. This disease, caused by the fungus Sclerotinia sclerotiorum, persists in the soil for many years as small black structures called sclerotia. In the spring, germinating sclerotia produce reproductive structures called apothecia, which produce spores that infect young stems or senescing plant parts such as blossoms.

Infection is most severe in densely planted stands that have complete canopy closure. These conditions increase the moisture level near the base of the plant, stimulating spore production and infection. Infected plants typically produce a white, moldy growth on the lower portion of the stem. This growth can also appear on the other portions of the plant. Eventually, sclerotia form within the infected issue.

Controlling white mold is difficult since the fungus persists in the soil. Carefully remove infected material and destroy it. Do not allow sclerotia to fall to the soil. Properly space plants during planting. Rotate plants whenever possible and plant non-susceptible varieties. Mulch plants to reduce spore dispersal and water plants early in the day at ground level. Avoid over-watering plants and improve soil drainage, when possible. Fungicides may be applied as a soil drench or as a preventative during the flowering stage. Two fungicides labeled for Sclerotinia sp. include thiophanate-methyl and chlorothalonil.


Oak Wilt
Chad Behrendt, Extension Plant Pathologist

oak wilt-tree
Oak wilt-tree
Photo credit:
Robert Blanchette
oak wilt leaf
Oak wilt-leaf
Photo credit:
Plant Disease Clinic
Oak wilt is a common and devastating disease of oak trees. Sap-feeding picnic beetles (Nitidulid beetles) carrying the oak wilt fungus initially infect trees as they feed and interact with fresh wounds. Once the tree is infected, the fungus moves through below-ground root grafts to adjacent healthy trees.

As the oak wilt fungus infects the tree, the tree tries to defend itself by producing inhibitory defense compounds. These compounds plug the water-conducting tissue causing the tree to wilt. Oak wilt typically causes yellowing, wilting, or browning of the leaves in the upper canopy. Eventually, these leaves fall from the tree. As the disease continues to infect the tree, wilt symptoms continue to move down towards the base of the tree. Individual leaves may also appear wilted with the margin of the leaf turning yellow, brown, or olive-green while the base of the leaf remains healthy and green.

All species of oak trees are susceptible to oak wilt with trees in the red oak group, including red and pin oaks, being highly susceptible. These trees usually die within a few weeks to one month. However, trees in the white oak group, including white and bur oaks, are more resistant and may survive for one or more years following infection.

The wilt-like symptoms produced by oak wilt are often confused with other stress-related factors such as construction damage, drought stress, or insect colonization (two-lined chestnut borer). In addition, oak wilt is often confused with the common springtime disease anthracnose. In contrast to oak wilt, anthracnose causes spotting, curling, and browning of the leaves in the lower canopy. Oak wilt may also cause brown streaking of the inner sapwood. This streaking is a good diagnostic symptom for detecting infected trees.

To prevent infection, avoid wounding trees during April, May, and June when the vectoring Nitidulid beetles are active. If trees are wounded during these months, prevent beetles from interacting with fresh wounds by painting them. Apply a water-based paint or shellac within minutes. These materials act as a protective barrier; they do not help the tree heal. Since the chance for infection still exists during July, August, September, and October, the optimum time for pruning trees is during dormancy.

To manage existing infections, use a vibratory plow with a five-foot blade to sever below ground root grafts and remove infected trees. Infected trees should be destroyed, or covered with heavy plastic through June of the following year. The systemic fungicide Alamo can be used as a preventative treatment in highly valued red and white oaks, and as a curative treatment in white oaks.
Test your diagnostic savvy monthly with Disease Watch at: http://www.extension.umn.edu/projects/yardandgarden/Plpa.htm


The Development of New Garden Chrysanthemums
Neil O. Anderson, Flower Breeder/Geneticist

Roseblush
'Rose Blush'
Photo credit: Dave Hanson,
U of M Extension Service
Background. The University of Minnesota Garden Chrysanthemum breeding project began in the 1930’s as an ornamental breeding program under the direction of Dr. Louis Longley. The breeding program has been in continuous operation since its inception, having released >70 cultivars to the marketplace. The program is now one of the few herbaceous ornamental breeding programs remaining at a public institution.

The rich history of the program, spanning more than six decades of research and development, is a fascinating record of breeding, selection, and the domestication of garden chrysanthemums for northern gardens. Initially, Dr. Longley began breeding greenhouse "mums". This was before the concept of photoperiodism had been documented and no one was aware what controlled flowering in mums. Photoperiodism is a physiological mechanism in plants that regulates whether they flower or remain vegetative (nonflowering). Plants can perceive the duration of darkness or the length of the night as a means of switching from vegetative to flowering. Originally, it was thought that it was the light or day period that was critical. Thus, plants were called short day or long day plants. Mums are classic short day plants, meaning that they perceive long night periods to initiate and development flowers. This is why mums normally flower in the fall, when the days become increasingly shorter and the night or dark periods become correspondingly longer. Dr. Longley released several greenhouse mums for northern growers (see Table).

Inca
'Inca'
Photo credit: Dave Hanson, U of M Extension  Service
Subsequently, the mum breeding emphasis changed objectives to concentrate on the development of garden mums. At that time, the only chrysanthemums being grown in North America were greenhouse cultivars that were restricted to indoor use. If a Minnesotan had wanted to grow a fall mum outside the only choice would be to take a greenhouse cultivar and plant it outside. These early greenhouse cultivars took a long time to flower since they had a long number of short days to initiate flowers, e.g. in some cases it took an exposure period of 84+ days of long nights (short days) before they would flower. A mum planted outdoors in Minnesota would not begin to perceive the "long nights" until late in the summer and into the autumn which meant that these greenhouse cultivars would not flower outside before a killing frost! Dr. Longley was a visionary and focused on the eventual domestication of garden mums as a separate class of chrysanthemums, distinct from greenhouse cultivars. He amassed a collection of wild species that served as the genetic base. For many decades, he bred, selected, reselected, trialed, and then released many garden mum cultivars (see Table). The initial releases flowered, although they were somewhat late in the fall. As the years passed, the breeding and selection resulted in earlier and earlier flowering garden mums. This germplasm, as well that from other mum breeding programs in public (Nebraska, Morden [Canada], etc.) and private (Yoder Brothers, Barberton, Ohio) institutions, served as the basis for the domestication of a separate class of mums that we refer to as "garden mums". It is the direct result of Dr. Longley’s efforts that we can grow garden mums in Minnesota and enjoy their flowers long before a frost arrives. In fact, some cultivars have frost tolerance and may flower until a freeze.

There are currently several hundred cultivars of garden mums available. The quantity of garden mums sold in 1997 was 46.9 million, compared with sales of pot mums of 27.6 million, and 12.1 million cut mums. Both potted and cut mums are known as "greenhouse" mums. The value of garden mums sold was $73.2 million. The production of garden mums has increased by 17% from 1993 to 1997, whereas the production of potted and cut mums have decreased by 16% and 63%, respectively. The wholesale value of garden mums has increased at a faster rate than total production has increased, due to the tendency of growers to market mums in larger container sizes for which consumers are willing to pay higher prices. The total dollar value of potted mums sold is greater than that of garden mums because potted mums are sold for prices two to three times that charged for garden mums in the same pot sizes.

mumbreeders
Neil Anderson and Peter Ascher evaluate field trials.
Photo credit: Dave Hanson, U of M Extension  Service
Later breeding objectives focused on improving the plant habit, shape, flower size and color. Dr. Richard Widmer directed the breeding program when Dr. Longley retired. Dr. Widmer and his research team of graduate students and a technician contributed many significant findings to the breeding efforts, including the release of a series of cushion mums known as the "Minns", optimal temperatures and nutrition for enhanced seed production. Dr. Widmer released many cultivars and was the first to apply for a plant patent. ‘Minngopher’ was patented and grown commercially for many years by the floricultural trade. Dr. Peter Ascher joined with Dr. Widmer to focus additional research on pollination biology, genetics, the development of inbred parents, and seed-propagated F1 hybrids. After Dr. Widmer’s retirement, Dr. Ascher continued the breeding program.

I was a graduate student with Drs. Ascher and Widmer and received my MS and PhD working on garden mums. After receiving my PhD, I worked in the breeding program focusing on new product development, release of additional new cultivars, and seed-propagated F1’s. At that time, Dr. Ascher and I worked with wild chrysanthemum species to further enhance and modify the garden mum characteristics. Of particular interest was the improvement of winter hardiness. Many consumers assume that garden mums are "hardy mums" when that has rarely been the case. Early work by Dr. Longley did produce winter hardy mums but subsequent breeding objectives did not always include this important trait. The commercial breeders have not used winter hardiness as a selection criteria, since the annual sale of garden mum cuttings keeps consumer demand high. Sale of winter hardy or perennial mums would significantly reduce the market potential for garden mums.

Betty Lou
'Betty Lou' Maxi-Mum
Photo credit: Dave Hanson, U of M Extension  Service
As a means of improving winter hardiness, we screened many different wild chrysanthemum species that had different growth habits. Some were also very winter hardy. A gardening friend happened to be growing a wild species that year and had some garden mums growing nearby. She noticed that seed was being produced on the wild species and wondered whether or not chance hybridization with the garden mum had occurred. We received the seeds from her that fall and grew them out the next year for evaluation. To our surprise we saw many different interspecies hybrid plants that looked very different from anything we had ever seen. Out of these plants we developed a new series of mums, known as "Maxi-Mumsä ", that have unusual growth characteristics. These are vigorous, winter hardy mums that have large plant growth in the second and subsequent years after planting. They can achieve a height of 3-4 feet and a single plant can have a diameter of 3-5 feet; flowering into the late fall as some have frost tolerance.

This year I assumed the directorship of the mum breeding program; Dr. Ascher will continue to advise with the project until his retirement. I will continue the breeding efforts to expand the genetic base of garden mums for northern gardening conditions. Our research will continue releasing cultivars for the existing series, especially Maxi-Mumsä , as well as development in new directions.

Recent Introductions. Some of the recent releases from the University of Minnesota breeding program include ‘Betty Lou’, ‘Inca’, ‘Rose Blush’, and ‘Snowscape’ (see photos). ‘Rose Blush’ was released in 1993 and has a mauve-colored flower. ‘Inca’ is a light bronze button type that fade pleasantly as each flower ages, giving the appearance of hammered bronze. ‘Snowscape’ has white flower petals tipped with purple. It tends to have a plant habit that resembles drifts of snow in the winter when the sunshine rays add tinges of pinks and purple. ‘Betty Lou’ is the first Maxi-Mumä to be released. It has maroon button-type flowers.

Ask for these Minnesota garden mums are your local garden center. If they do not carry them, the garden center can contact the following Minnesota mum propagators:



Snowscape
'Snowscape'
Photo credit: Dave Hanson, U of M Extension  Service
The Breeding, Development, and Release of New Introductions. Many gardeners are unaware of the complicated series of events involved with the breeding, selection, and release of new flowers for their gardens. Flower breeding, especially when working with herbaceous perennials, is a lengthy process. It may take 5-10 years to release a garden mum after the initial cross was made that produced the hybrid plant. For more complicated plant growth types, such as Maxi-Mumsä , more time may be required.

The breeding process starts with clear breeding objectives or directives. For example, early flowering mums was Dr. Longley’s primary breeding objective. He amassed a wide diversity of mum germplasm and flowered it outside in field trials to select the earliest flowering material that he could find. In the fall, he then intercrossed these early selections among themselves, as well as with wild species to create a set of F1 hybrids. Seeds from these crosses were planted the following spring in flats, transplanted into the fields in St. Paul, and then grown for fall flowering. He examined these that next fall to see which set of hybrids had any early flowering individuals. Eventually, after several years of selecting, recrossing, and evaluating hybrids he found what he was looking for. These early selections became the base for continued breeding.

After an initial selection has been made that meets the breeding objective(s), it must be rooted as a cutting to increase the number of available plants (clones) of that selection. If they root successfully, 10-24 cuttings will be planted in the field for evaluation that year. If the plants appear free of disease, flower uniformly, and have good plant shapes, this is selected for additional years’ trialing both in St. Paul and other locations. The breeding program also evaluates selections at the various agricultural experiment stations across the states, including Morris, Grand Rapids, Waseca, Crookston, Lamberton. A selection may be trialed for 3-4 years at all sites where they are all rated yearly for flowering and winter survival before a decision is made regarding release.

Upon release, publications are issued for each new garden mum by the Minnesota Agricultural Experiment Station. These are available as Distribution Center Publications, known as Minnesota Reports. From there, it is anticipated that commercial propagators and distributors will license a new release and sell it on the market. Part of the license agreement stipulates that royalties monies flow back to the breeding program to ensure the continued release of new cultivars in the future. If a release is patented to protect it from being stolen, royalty money also reverts back to the program from the sale of the patented cultivar. This royalty money is useful for the breeding program to continue operating.

Next time you look at your garden mums that you have growing in your garden or in containers on your deck or patio, think of the many steps involved in the creation of that one unique cultivar. Be sure to watch your garden center for the next releases from the University of Minnesota releases, especially new Maxi-Mumsä !

University of Minnesota Chrysanthemums (garden types)

(chronological order)

'Duluth’

1939

2-inch, lemon-yellow, semi-double flowers

'Boreas’

1941

2-inch, white double flowers

'Harmony’

1941

2.25-inch, yellow to red double flowers

'Moonglow’

1941

l.75-inch, lemon-chrome double flowers

'Redwing’

1941

l.75-inch, red, semi-double flowers

'Welcome’

1941

l.75-inch, mallow-purple semi-double flowers

'Chippewa’

1942

2.75-inch, purple semi-double flowers

'Purple Star’

1942

2-inch, purple double flowers

'Redgold’

1942

2-inch, scarlet pompon flowers

'Sunred’

1942

3-inch, Brazil red semi-double flowers

'Pipestone’

1943

2.75-inch, Brazil-red semi-double flowers

'Waterlily’

1943

3-inch, raspberry double flowers

'Butterball’

1944

2.5-inch, lemon-chrome pompon flowers

'Glacier’

1944

early, 3-inch, white decorative flowers

'Redhawk’

1944

2-inch, red quilled flowers

'Redwood’

1944

2-inch, carmine semi-double flowers

'Snowball’

1944

2.5-inch, white double flowers

'Aurora’

1945

2.25 -inch, blood-red double flowers

'Maroon'n Gold’

1945

3.5-inch red to maroon double flowers

'Dee Dee Arens’

1946

2-inch, white double flowers

'Violet’

1946

3-inch, purple double flowers

'Brilliant’

1947

cushion, 2.5-inch, Brazil-red, double flowers

'Silver Pink’

1947

2.5-inch, pink with silvery sheen, double flowers

'Bountiful’

1948

2.5-inch, carmine double flowers

'Dr. Longley’

1949

3-inch, rose-pink decorative flowers

'Moonlight’

1949

3-inch, pale yellow reflexed flowers

'Harvest Bronze’

1952

3-inch, apricot-bronze double flowers

'Prairie Sunset’

1952

2.5-inch, rose-pink double flowers

'Wenonah’

1954

2.25-inch, lavender double flowers

'Mesabi’

1955

2-inch, copper-red double flowers

'Vulcan’

1955

2.5 inch, dark red decorative flowers

'Wanda’

1956

3-inch, raspberry double flowers

'Golden Fantasy’

1957

2-inch, golden yellow decorative flowers

'Minnbronze’

1957

Cushion, 1. 5-inch, bronze double flowers

'Minnpink’

1957

Cushion, 1. 5-inch, rose-pink decorative flowers

'Princess’

1957

2-inch, rose and gold flowers

'Minnehaha’

1958

2.5-inch, salmon double flowers

'Prairie Moon’

1959

4-inch, creamy-white double flowers

'Tonka’

1959

3-inch, yellow double flowers

'Wayzata’

1961

3-inch, bright yellow decorative flowers

'Minnautumn’

1962

Cushion, 2.5-inch reddish bronze decorative flowers

'Tenstrike’

1963

l.5-inch, bright lavender pompon flowers

'Gold Strike'

1964

2-inch, golden yellow pompon flowers

'Zonta’

1964

2.5-inch, apricot-bronze pompon flowers

'Superior’

1965

3-inch, bronze-orange decorative flowers

'Creamtop’

1966

3 -inch, white flowers with yellow centers

'Minnrose’

1966

Cushion, 1. 5-inch, rose-pink pompon flowers

'Minnwhite’

1968

Cushion, 2-inch, white decorative flowers

'Sunny Glow’

1968

2.5-inch, orange-gold decorative flowers

'Royal Pomp’

1969

2" pompon-spicy fragrance, bright purple flowers

'Yellow Glow’

1969

2.75-inch, rich yellow decorative flowers

'Golden Jubilee’

1971

3-inch, deep gold decorative flowers

'Minneglow’

1972

Cushion, 2.25-inch, lemon-yellow decorative flowers

'Minnyellow’

1972

Cushion, 2-inch, lemon-yellow decorative flowers

'Lindy’

1974

4 1/2" lavender-pink, quilled incurve flowers, tall

'Minnruby’

1974

Cushion, 2.25-inch, ruby-red decorative flowers

'Wendy Ann’

1974

4-inch, fawn yellow semi-spoon flowers

'Autumn Fire’

1977

large, double, burnt orange flowers

'Golden Star’

1977

yellow, spoon-petalled flowers

'Minngopher’

1977

Cushion, 2.0-2.5-inch. ruby-red decorative flowers

'Minnqueen’

1979

Cushion, 3-inch, rose-pink decorative flowers

'Royal Knight’

1979

Burgundy, silver underside, 3 1/2" reflexed decorative

'Centerpiece’

1982

4" rose-lavender with gold center, quilled flowers, tall

'Gold Country’

1983

4 inch, peachy yellow, fully double decorative flowers

'Mellow Moon’

1983

Cream, 4 1/2" semi-incurved, fully double, decorative

'Centennial Sun’

1985

golden yellow, 1.5" double decorative, early

'Rosy Glow’

1987

deep rosy pink, 4" decorative incurved

'Burnt Copper’

1988

orange bronze, 3" double pompon, tall, midseason

'Grape Glow’

1988

bright rosy purple, 3 1/2" flat decorative

'Lemonsota’

1988

lemon yellow, 1" pompon, low

'Maroon Pride’

1989

dark red, 3 1/2" flat, decorative, early

'Snowsota’

1989

white with cream centers, 1 1/2" pompon

'Rose Blush’

1993

mauve, 2-3" decorative

'Betty Lou’ Maxi-Mumä

1996

red, button, 30 inch spread

'Inca'ä

1996

light bronze, 2" double button, low

'Snowscape'ä

1996

white with purple tips, 3" semi-double, decorative flowers

Chrysanthemums (greenhouse types; few descriptions available, chronological order)

'Daisy mum’

1940

Single, white starlike flowers

'Hiawatha’

1934

  

'Fawn’

1935

  

'Northstar’

1935

  

'Snowflake’

1935

single, rays aster-purple, twisted

'Sioux’

1940

  

'Winona’

1940

single, lemon-chrome flowers

Editorial Notes

gertens
Gertens Garden Center, Inver Grove Hts.
Photo credit: Beth Jarvis
Sorry for being a bit late with this issue; t'was a minor technical difficulty.

Coming next issue: Mike Zins, from the Arboretum, is going to write about overwintering marginally hardy plants. In future issues: preventing winter injury in trees and shrubs, is it worthwhile to know your apple's rootstock?, mycorhhizae, and what's new in the blueberry patch?

I'm still collecting suggestions for articles for the near future or even for next year. Drop me a note if you have ideas.

Deb Brown is a regularly scheduled guest 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.

I put up a small webpage with the Yard & Garden Line promotional items that are available, at no charge, of course. It's at: http://www.extension.umn.edu/projects/yardandgarden/YGLpromos.html.

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, the Water Line, INFO U and the Soil Testing Lab. You'll also find links to the current issue of the Plant Health Care Update and back issue archives. Plant Health Care Update is a newsletter written by Master Gardeners for Master Gardeners. The authors have completed advanced training to earn the designation Plant Health Care Advisors.

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: 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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