Yard & Garden Line News Volume 2 Number 4                                                              April 1, 2000

Features this issue: The Scoop on Vermiculite for Potting Mixes and Garden Beds Effect of Mild Winter Weather on Insect Numbers Spring Bulb Basics Weed Control in Gardens Iris Borers Are Active in April Be Prepared for Spring Diseases - Monitor the Weather Ladybird Beetles and Asthma Stop Pruning Your Oak Trees! Apple Scab Reminder Diagnosing Lawn Diseases Editorial Notes

The Scoop on Vermiculite for Potting Mixes and Garden Beds
Carl Rosen, Extension Soil Scientist
Department of Soil, Water, and Climate

Vermiculite Photo credit:  U of MN Extension Service

Recent publicity about asbestos-contaminated vermiculite from the Libby mine in Montana has caused concern among those who have used this amendment for potting mixes and garden beds. While the major heath risks associated with asbestos-contaminated vermiculite are more likely from attic insulation uses, questions about garden uses are also being asked. The most frequently asked questions are: 1) what should be done with garden beds where the contaminated vermiculite was used? and 2) is the vermiculite available for potting mixes today safe to use? To help answer these questions a brief review of what vermiculite is, where it comes from, what it is used for, and how some sources became contaminated will be addressed in this article.

Commercial vermiculite is a naturally occurring mica mineral (technically biotite and iron bearing phlogopite) that is mined in various locations around the world. When exposed to high temperatures the vermiculite expands to about 15 times its natural size. The resulting product has a very low density making it suitable for a variety of uses including insulation, packing material, potting soil, fireproofing, and cement mixes.

In potting mixes, vermiculite provides porosity to the mixture while at the same time retains water making it an ideal amendment for growing plants in containers. Usually the potting mix contains 5 to 50% vermiculite by volume, with peat, perlite, sand, or soil comprising the rest of the mixture in various proportions. Vermiculite can also be used in garden beds to loosen up clay soils. Over time however, the vermiculite tends to compact and will lose its desirable properties. The difference between potting mix vermiculite and insulation vermiculite is primarily particle size - with smaller size particles used for the potting mixes.

Petunias are just a one of the bedding plants grown in vermiculite mix. Photo credit: Beth  Jarvis

Up until 1990, about 70 to 80% of the vermiculite used in the U.S. was mined in Libby, Montana. The processed vermiculite from Libby was often sold under the trade name "Zonolite". W.R. Grace was the company that owned the mine from 1963 - 1990. A problem specific to the Libby mine was that the vermiculite deposit was also associated with tremolite asbestos, a rare naturally-occurring mineral. Health problems associated with asbestos have been known for many years; however, it is uncertain just how long the health problems have been known at the Libby plant. Due to the high amount of asbestosis, lung cancer, and mesotheloioma related deaths among workers and family members associated with the Libby plant, the mine was closed down in 1990. Because ten years have passed since the closing of the mine, it is unlikely that any of the vermiculite used today comes from the Libby, Montana mine.

Vermiculite is currently mined in South Carolina and Virginia as well in South Africa, Brazil, China, Egypt, India, Japan and Russia. The largest mine today is located in South Africa. No asbestos related disorders have been reported in any of the major vermiculite mines except for the Libby, Montana mine. Testing done by EPA and the Ontario Research Foundation found that no asbestos could be detected in the vermiculite from the South Africa mine. Based on these reports, it can be reasonably assumed that vermiculite used today does not contain significant amounts of asbestos.

When using vermiculite, as well as any other material that inherently contains dust sized particles, it is recommended that dust control measures be adopted and/or personal protective equipment (dust masks) be used to protect against dust inhalation. Keeping the vermiculite moist will greatly reduce dust problems.

If it is known that Libby vermiculite was used in a garden bed, health risks can be reduced by simply covering the area with sod or mulch to ensure that dust from the area is kept to a minium. As a last resort the area can be excavated by professionals and sent off to a landfill.

For further information on vermiculite and health related issues please refer to the following web sites:

http://www.vermiculite.org
http://www.epa.gov/region01/qa.html
http://www.mcn.net/~vermiculite/overview.htm

Effect of Mild Winter Weather on Insect Numbers
Jeffrey Hahn, Assistant Extension Entomologist

What effect will our mild winter have on insect populations this year? Not as much as people think. Certainly, insects have had a greater chance of surviving this year's mild weather compared to a harsh winter, but the overall effect is most likely minimal. There may be some insects that benefit from the moderate temperatures but overall we are not likely to see noticeably large numbers of insects because of the mild January and February temperatures. However, our spring and summer weather will have a much larger impact on insect populations. For example, if we have a rainy spring, that will lead to large mosquito populations. A warm, dry spring encourages large wasp numbers. A hot, dry summer, is favorable for spider mites (an insect relative). Different types of weather will affect insects differently. It will be hard to predict these patterns until we get further into the spring.

Spring Bulb Basics
Deborah Brown, Extension Horticulturist

A cheery display of tulips. Photo credit: Deb Brown

Every year some gardeners are disappointed by the performance of their spring-flowering bulbs. Often, weather conditions such as our early spring warm up, followed by freezing cold this year are responsible for their poor showing. But not always. Sometimes the site or growing conditions after blooming contribute mightily to the problem.

Here are some of the common mistakes people make in caring for their spring bulbs:

* Planting where there isn't enough sunlight

Though daffodil foliage hangs around a long time, most spring bulb foliage is short-lived. That means they need to pick up plenty of sunlight for photosynthesis/food production in a relatively short period of time. The sunnier the location, the more food these plants can store for the following year.

* Planting in poorly-drained soil or low-lying areas where water puddles after heavy rainfall

Because bulbs are mostly fleshy stem tissue (roots form at the base of the bulb; the bulb itself is not a root), they are prone to rotting when kept too moist. Prepare your bulb bed by digging soil several inches deeper than where you intend to plant, then amending the soil with well-rotted compost.

You can also compensate to some degree by not planting bulbs as deeply in heavier soil, but if they're too shallow the bulbs will be more vulnerable to problems associated with winter cold and exposure.

* Removing foliage soon after blooming

Don't become obsessive or impatient in your quest to "tidy up" the garden or replant the area with annuals. The longer you can keep that bulb foliage healthy, the better your bulbs' prospects for the following year. In fact, it's a good idea to fertilize them, using a liquid or granular product -- whichever is easier -- while foliage is still green.

* Interplanting with moisture-demanding annuals

Unless your soil is very sandy, this can be a real problem. If you choose to interplant fading bulbs with flowering annuals, pick ones that have modest moisture demands. Marigolds, petunias, moss roses, vinca or creeping zinnia are a few possibilities. They like the same sunny growing conditions as your spring bulbs, and they don't demand as much moisture as some annuals, which means there's less likelihood your bulbs will rot.

* Expecting too much from them

Though hyacinths bloom beautifully here the first year, they rarely produce large flower clusters after that. Most tulips grow smaller and produce fewer flowers from year to year. Even daffodils can peter out after a few years unless they're growing in ideal circumstances. If your bulbs were sparse this year, don't expect them to come back better next spring. Instead, dig them up after the foliage dies back, and save only the largest bulbs for replanting next fall.

Weed Control in Gardens
Deborah Brown, Extension Horticulturist

No weed control needed at this house. Photo credit: Deb Brown

Controlling weeds can be a tricky business in gardens. The very substances that kill your weeds are also capable of killing your flowers or vegetables; they simply don't discriminate between "good" plants and "bad" ones. Let's look at cultural methods of managing garden weeds first:

* When starting a new garden, take extra time to get rid of all the perennial weeds in the area before you plant. Do whatever you have to, including using glyphosate (Roundup), to eliminate quack grass, thistles, and other tough weeds that survive our winters. Once your good plants are growing in the garden, it will never be as easy to go after those tough weeds.

* Mulch between plants as soon as soil warms sufficiently; even earlier where you grow "cool season" plants like peas, cabbage, broccoli, pansies, stocks, or calendulas. Mulch keeps needed sunlight from reaching many annual weed seeds, effectively stopping them from germinating. Those that do sprout may be pulled out easily because mulch prevents compaction and keeps soil loose and crumbly. Unfortunately, mulch will not stop most tougher perennial weeds.

* Preemergence herbicides such as Preen or one of the all-natural corn gluten meal products will prevent annual weed seeds from sprouting in your garden. But before applying them, your desired seeds must be up and growing or the herbicide will stop them, right along with the weed seeds. Young transplants such as tomato or pepper plants must have spent a couple weeks in the garden so they have plenty roots, before it's safe to use a preemergent product nearby. Read product labels carefully for specific details.

Mulch prevents most annual weeds from sprouting. Photo credit:  U of MN Extension Service

By the time you can put down preemergence herbicides, early weeds have usually begun to sprout. You'll just have to remove these manually or with a sharp hoe before applying herbicide to the soil.

* There is a grass-killer made by Ortho, that can be safely used in a flower garden. When you spray, it will only kill grassy plants, not most flowering plants. Again, read the label carefully before applying it.

You can also wipe glyphosate onto individual plants you want to eliminate, as long as no chemical reaches nearby flowers or vegetables. Use a sponge on a stick or put on a thick rubber glove, then a cotton garden glove over it, and dip your gloved hand into a shallow container of the herbicide so you can wipe the weeds easily.

* And finally, stay vigilant all summer. So often people give up on weeds towards the end of the season when most vegetables are mature or have been harvested and flowers are growing vigorously. Heat, mosquitoes, alternate types of recreation, and just a general sense of winding down may mean that many weeds are allowed to grow and set seeds, unchecked, towards the end of August.

Unfortunately, those weed seeds will drop to the soil where they'll sprout next year and for years to come. It's really worth your while to keep removing them, right until freezing temperatures spell their demise until the following spring.

Iris Borers Are Active in April
Jeffrey Hahn, Assistant Extension Entomologist

Iris borer. Photo credit: Jeff Hahn

Protecting iris from iris borers is usually a challenging task for gardeners. These pests can be managed with an insecticide treatment but the correct timing is critical. During a normal spring, the overwintering eggs usually hatch sometime in April when new growth is about four to six inches tall. Because of our warm temperatures in early March, iris new growth may already be four to six inches tall. However, gardeners need to be careful this spring about using plant phenology to determine the proper time to spray iris borers. It is unlikely that iris borer eggs have hatched yet, especially with recent temperatures in the 30's and 40's (degrees Fahrenheit). Even though your iris may already have four to six inches of new growth, it is probably better to wait to spray until we are more consistently in the 50's (degrees Fahrenheit). The most effective insecticide against iris borer is Cygon 2E (dimethoate).

Be Prepared for Spring Diseases - Monitor the Weather
Chad Behrendt, Extension Plant Pathologist

Oak anthracnose on branch. Photo credit: Chad Behrendt.

People are always wondering what diseases are going to be severe this year, and how they can prepare for them. Unfortunately, there is no simple answer. Plant disease is best described by the plant disease triangle. As detailed in last month's Yard and Garden News, the disease triangle consists of three components: susceptible host, virulent pathogen, and conducive environment. All three components are required before disease can occur.

Since any plant can be considered a host and many virulent pathogens occur naturally in the landscape, it is the environment that regulates plant disease. Temperature and moisture are the two factors regulating disease with moisture being the most important. As a result, we usually see more plant disease when we receive heavy, frequent spring rains. Both fungi and bacteria require a minimum temperature in order to become active. Neither can germinate, infect, or reproduce without free moisture (rain), regardless of temperature. Therefore, one can predict the incidence and severity of many diseases by monitoring the amount of rainfall.

In 1998 the Twin Cities received 1.6 inches of rain during the month of April and 4.4 inches in May, while 3.4 and 6.6 inches fell in April and May of 1999. This correlates with the little plant disease observed in 1998 and the very high levels in 1999. Apple scab in 1998 caused only a few lesions to develop on the leaves of crabapple trees, while most of the leaves were infected in 1999. In addition, many of the infected leaves turned yellow and dropped from the trees in 1999. We also observed many unusual or uncommon diseases in 1999, such as willow scab, bacterial soft rot, and severe anthracnose.

To manage plant disease this year, begin monitoring rainfall this April. If we receive large amounts of rain or prolonged periods of rain are predicted, you may consider applying a preventative fungicide for those diseases that have been a problem in the past. Common diseases such as apple scab, anthracnose, powdery mildew, and fireblight often become severe with heavy spring rains. In addition, you can help reduce moisture levels by maintaining proper spacing and good airflow.

Ladybird Beetles and Asthma
Jeffrey Hahn, Assistant Extension Entomologist

Multicolored Asian Ladybird Beetle Photo credit: Jeff Hahn

Multicolored Asian ladybird beetles are a nuisance because they overwinter in and around structures. With the onset of mild February and March weather, this species of ladybug has emerged from their overwintering sites and have become trapped indoors. Even though these insects are annoying, they are considered harmless.

However, there have been a recent case that links multicolored Asian ladybird beetles with asthma. According to Dr. Hobert Pence, a Louisville, Kentucky allergist, a man in southern Indiana was found to have elevated levels of allergic antibody in his blood to ladybug proteins. He did not suffer asthma symptoms until his house was infested with thousands of ladybugs. His symptoms were severe enough to require medication.

It remains to be seen whether this will become anything more than a rare problem. However, it would be reasonable to assume that the frequency of cases will at least increase somewhat as people are increasingly exposed to ladybugs. Live ladybugs, as well as accumulations of dead ones, will help contribute to asthma problems.

If you have a problem with ladybugs in your home now, the best course of action is to vacuum them as you see them in your home. Insecticides are not necessary to control ladybugs in spring. You can minimize a ladybug problem next fall by sealing cracks, spaces, and gaps around the exterior of your home by the end of summer. You can supplement this with an insecticide application around your home's exterior when these insects first start to appear in October.

Test your diagnostic savvy monthly with Disease Watch at: http://www.extension.umn.edu/projects/yardandgarden/Plpa.htm
Stop Pruning Your Oak Trees!
Chad Behrendt, Extension Plant Pathologist

Oak wilt mat and beetles. Photo credit: Dept. of Entomology

Reminder Photo: MDA

Every April the Yard and Garden Clinic receives numerous calls from home-owners, asking if they can still prune their oak trees. The answer is NO. Oak trees can be pruned only from July - March, with the optimum time or 'No Risk Period' being November - March. From July - October pruning is allowable if necessary, but there is still a small risk of oak wilt infection during those months. The new oak wilt guidelines now divide the year into High Risk (April - June), Low Risk (July - October), and No Risk (November - March) periods. For more information on pruning guidelines see the Oak Wilt in Minnesota Publication (http://www.extension.umn.edu/distribution/naturalresources/DD3174.html).

Although these recommendations provide a time frame for pruning, it is important to remember that they are only guidelines. In other words, the chance or risk of infection increases as we approach April and decreases as we approach July. One should always consider current conditions in addition to the general guidelines. This year, for example, both the Nitidulid beetles, vectors of the oak wilt fungus, and the oak wilt fungal mats became active in mid to late March. However, beetle and fungal spore populations will not maximize until April or May.

If oak trees are accidentally wounded or pruning is unavoidable, paint the wound immediately with a water-based paint or shellac. This coating acts as a barrier to prevent the introduction of fungal spores, but does not help the tree to heal.

Apple Scab Reminder
Chad Behrendt, Extension Plant Pathologist

Photo credits: Plant Disease Clinic

If you are following a preventative fungicide spray program for apple scab, you should be applying your first spray when the new growth is ½ inch in length. (This stage is called ½ inch green tip.) The second spray should be applied when the flower buds begin to emerge and show color. For more information see the Home fruit Spray Guide (http://www.extension.umn.edu/distribution/horticulture/DG0675.html).

To minimize fungicide applications, monitor the weather forecast. If no rain is predicted at the time of your scheduled spray, you can delay or skip that spray, until rain is predicted. In addition, summer sprays can be discontinued if no scab lesions are observed by the end of June.

Diagnosing Lawn Diseases
By Crystal Floyd, Plant Pathology technician

Rings in turf. Photo credits: Plant Disease Clinic

Diagnosing a problem in the lawn can be difficult. Problems may be caused by disease, but may also be due to abiotic (non-infectious) factors such as drought, inadequate light, dog urine, herbicide spills, or fertilizer burns. Before trying to diagnose your lawn disease, try to eliminate these other causes.

For easier diagnosis, lawn diseases generally fit into three different categories: Ring spot diseases - bleached, brown, or dead rings of grass Patch diseases - round to irregular-shaped bleached, brown, or dead areas of grass Leaf diseases - thinning areas with spotted grass blades or visible fungal growth on the blades

Ring spot diseases include fairy rings, necrotic ring spot, and yellow patch. Fairy rings are large rings up to thirty feet in diameter. Mushrooms often appear around the dead rings of grass. Necrotic ring spot and yellow patch cause smaller rings, usually less than one foot in diameter. Rings often coalesce forming large irregular patches of grass. Necrotic ring spot and yellow patch cannot be differentiated without microscopic examination.

Patch diseases include snow mold, brown patch, summer patch, and Pythium blight. In addition, necrotic ring spot and yellow patch often form irregular patches when ring spots coalesce. Snow mold appears after snow melt in the spring. The patches are matted and colored white, pink, or gray. The rest of the patch diseases occur at various times from late spring to late summer. They are difficult to differentiate and require microscopic examination.

Leaf diseases are some of the easiest to identify. They include leaf spot/melting out, red thread, rust, powdery mildew, and slime molds. Leaf spot and melting out produce characteristic tan, circular leaf spots with dark purple to brown margins. Red thread is identified by red, thread-like fungal growth, often resembling miniature tufts of cotton candy, protruding from the tips of leaf blades. Rusts produce pustules on grass blades filled with orange, powdery spores. These spores are often apparent as an orange coating on shoes or lawn mowers. Powdery mildew causes a fine, white, powdery coating on grass blades. This coating can easily be rubbed off with your fingers. Slime molds are fungi that occasionally occur on grass blades, but are not pathogenic. Slime molds may appear as white or colored jelly-like masses that later turn dry and crusty.

Closeup. Photo credits: Plant Disease Clinic

The diseases mentioned above are those that are most commonly seen in Minnesota. Other diseases may occur in lawns. Regardless of what disease your lawn has, proper cultural practices are the most important management strategy. Properly water and fertilize lawns. Too much or too little can predispose your lawn to disease or increase its severity. Dethatch the lawn as needed. A thick thatch layer can contribute to disease. Fungicide applications may be necessary for certain diseases. A correct diagnosis of the disease is necessary. Fungicides are only effective when applied at the proper rate and time. Fungicides should always be used in conjunction with proper cultural practices.

If your lawn has some of the symptoms described above, or if you have eliminated abiotic causes and suspect you have a lawn disease, you may wish to submit a lawn sample to the Yard and Garden Clinic for diagnosis. Samples are most easily diagnosed while the grass is actively growing. The piece of turf submitted must be from the edge of the diseased area. This area is often referred to as the zone of transition. For example, if ring spots are visible in the lawn, cut out a piece of the ring showing the dead ring and the green healthy grass next to it. The piece should be approximately 4" x 8". Dig down about 6" to include the grass roots. A shoebox works well for delivering a sample. Take pictures of the lawn showing the symptoms and include at least one close-up of the diseased grass. The sample and photos can be brought in or sent to the clinic. There is a $5.00 fee for this service. For more information, refer to Submitting a Plant Specimen. at: http://www3.extension.umn.edu/projects/yardandgarden/Intake.htm)

Editorial Notes

Crocus, some of the first to bloom. Photo credits: Beth Jarvis

Such weather! It's been a theater of seasons all in one month from 70 above to snow!

Now down to the serious business at hand. Getting the garden planted. While it's still too chilly to plant outdoors, seed starting indoors is great fun. Many seeds should be started 6 weeks before last average frost date, so now is the time, here in the Twin Cities.

Speaking of seeds, Vince Fritz, our commercial vegetable expert, will write about seed germination for the April 15th issue. I also plan to have the long promised potato article. (If you have any questions you'd like me to add to my list, e-mail me before April 10th.)

Mary Blickenderfer, shoreline vegetation and landscaping specialist, will be sharing some ideas on landscaping around ponds in another issue.

I'm always looking for article ideas and have received some intriguing story suggestions. So, don't be shy!! Your story suggestions are most welcome!

We've just been told that the Water Line, a selection on the Yard & Garden Line has successfully concluded its mission and will be closed April 15. Information on water issues is available on-line from the Extension home page (www.extension.umn.edu) and county offices.

Here are some websites that you may find interesting.

The first one is the 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/

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.

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
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Happy gardening!

Beth Jarvis
Yard & Garden Line Project Coordinator

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