In the last issue, we alerted you that emerald ash borer was a mile away from the Minnesota border. On May 14, the Minnesota Department of Agriculture confirmed that the pest has been located in St. Paul, Minnesota. Keep up with the latest news on Extension's emerald ash borer response page.

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Downy Mildew, a potentially devastating fungal disease of roses has been found on several roses for sale in Minnesota. The disease has been identified on Double Knock Out®, Pink Knock Out® and Europeana®, but all rose cultivars are susceptible to Downy Mildew. This disease results in irregular purplish red leaf spots that eventually turn tan in the center. Infected leaves often turn yellow and fall off. Under very humid conditions gray fuzzy fungal growth may be seen on the underside of infected leaves. Downy Mildew also causes purplish black streaks on rose stems. Downy Mildew thrives under cool humid conditions. It spreads easily on the wind. If infected plants are brought into the garden, the disease could easily spread to other roses and raspberries in the area. Do not purchase roses with dark leaf spots!

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If you grow strawberries you are familiar with the spring and summer task of crawling through the rows pulling weeds. It’s a time consuming, arduous task, but a very necessary one. Weeds rob strawberries of valuable water and nutrients, resulting in reduced vigor and fewer, smaller berries. Hand weeding is just about the only way to remove weeds in a strawberry plot because mechanical removal can easily damage the low growing strawberry plants, and approved herbicides are declining in number and becoming more and more expensive. Additionally, consumer interest in local foods grown without such chemicals is rapidly increasing, leading growers to look for alternatives. So with few options other than growing strawberries with plastic mulch (which poses its own environmental problems), growers get on their hands and knees each year in an endless battle against the unrelenting weeds.

But now there is hope for the achy knees, sore backs, and tight schedules of strawberry growers. Wool mulch, cleverly named Woolch™, is marketed by the Minnesota Lamb and Wool Producers Association and has been studied for the past ten years at the University of Minnesota West Central Research and Outreach Center in Morris, and at several local farms. The results of 10 years of trials have shown overwhelming success of Woolch™ in reducing weeds in strawberry plots.

Woolch™ is a value-added product of the Minnesota lamb and wool industry. It is manufactured using short fiber waste wool from the carding process, in which raw wool is cleaned and separated before spinning. Similar short fiber waste wool is collected from the napping process of blanket-making at local woolen mills. These short fibers are combined with wood shavings from Minnesota timber mills through a heat and roller process, and the result is a lightweight felt-like mat that is completely natural and biodegradable.

Woolch™ works well with strawberries for several reasons. First, water and nutrients can move through it, daughter plants can root through it, but weeds neither grow up nor root down through it (except for quackgrass, which should be eliminated before planting). Second, it helps maintain soil moisture and moderates soil temperature. Third, it creates a barrier between the low growing strawberry and the soil which may harbor fungal diseases that can lead to reduced growth, poor yields and damaged fruit. In a similar vein, berries resting on Woolch™ remain cleaner and drier than those conventionally grown. Finally, Woolch™ breaks down over a couple of years, meaning it can then be tilled into the soil to add valuable nutrients.

Though not part of any research project, I can personally vouch for the success of Woolch™ in the home garden. Last season I planted vegetables and flowers in a veritable weed patch, and I expected to spend the summer battling the continual onslaught of weeds. Not this gardener! I ran a soaker hose throughout the beds to allow for direct and easy watering. I then cut pieces of Woolch™ to place around the plants, and cut slits to fit pieces around stems or rows of stems. I shoveled a bit of soil over the edges to keep the Woolch™ in place, and gave it a good watering from above to help it adhere to the soil. Throughout the season the soil remained moist and cool under the Woolch™, and the plants were vigorous and abundant. The only weeding I had to do was is in the paths between beds, which was quick and easy. This season Woolch™ will be used in a new edible landscape planting in the beds outside the Plant Growth Facility on the St. Paul Campus. Stop by and take a look at this innovative, effective, and totally natural product in action!

Woolch™ is available directly from the Minnesota Lamb and Wool Producers Association. For more information visit their website at http://www.mlwp.org/woolch.htm. You can support this local industry while benefiting your garden or small farming operation!

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Usually the middle to end of May is the prime time for putting down preemergence weed killer for crabgrass. In general early in the month is appropriate for the southern 1/3 of Minnesota while later in May is fine for middle to northern sections of the state. But what if I miss the prime window of application, how do I know if it’s too late to apply the product? That’s a good question. For all practical purposes, once the crabgrass seedlings have emerged from the ground it is too late for a preemergence product to effectively be put down. There is one notable exception and that is the preemergence weed killer known as dithiopyr. It is known in the trade by its product name Dimension. It is a common ingredient in many homeowner formulations. This product does provide some control of seedling crabgrass plants up until the 2 or 3 true leaf stage. That is still a pretty small plant. It is important to distinguish between tillers and leaves. Tillers are secondary shoots that also arise from the crown of the plant. See accompanying picture for a comparison of a two to three tiller stage compared to a two to three leaf stage. Applying dithiopyr at the two to three tiller stage is useless. It must applied prior to or at the two to three leaf stage to have any control effect. It should also be noted that dithiopyr will continue to have its preemergence effect once it’s applied as well as very early postemergence effect.

For creeping Charlie, second to fall treatment, spring time, at or during full bloom, is a very good time to apply postemergence herbicides to control this common lawn weed. However, rather than just simply reaching for an herbicide to kill the plant, stop and consider for a moment as to why this weed seems to be getting worse or expanding in your lawn. Creeping Charlie does best in a moist, partly shaded to fully shaded environment. As shade increases it becomes less and less favorable for sustaining a turfgrass cover and more and more favorable for weeds like creeping Charlie to encroach and take over. It might be that doing some pruning or other practices to get more light to the soil surface will improve growing conditions such that turfgrass can survive and thrive there. Then, if creeping Charlie is controlled with an herbicide you can come back and overseed with a shady lawn mix and expect it to be more competitive and vigorous thus helping to keep creeping Charlie from reestablishing. If the area is simply too shady to grow turfgrass, why fight it, consider other ground covers or a shade garden of perennial flowers. They are not necessarily less work than a lawn, but can provide a very attractive area in the landscape. If you are considering the use of an herbicide for controlling creeping Charlie, select one that contains the active ingredient triclopyr. Research has shown that the addition of this product to a broadleaf herbicide is more effective than those not containing it. You can even purchase products where triclopyr is the only ingredient. They are usually sold as a weed control products specifically for creeping Charlie, white clover, oxalis and other difficult weeds. For a listing of available home lawn and landscape weed control products, see the chart included in the update article in the May 15, 2008 Yard and Garden Newsletter.

Hot, dry periods during the latter half of May are not uncommon. Since spring is a very active period of growth for grass plants plus we are often putting down fertilizers and weed killers, it’s important to keep grass out of drought stress. Broadleaf weed killers such as those used for dandelions can injure or even kill lawn grasses that are under drought stress. A general rule of thumb for lawn watering is about 1 inch of water per week which includes what we receive through rainfall. Remember, it may be necessary to apply a couple of ½ inch applications on compacted soils, heavier clay soils and sandy soils rather than a single 1 inch application. In the compacted and heavier clay soils, too much water per application may cause ponding or water saturated conditions on the soil surface due to very slow water infiltration rates. This can damage or even cause dieback of roots in a matter of hours that are growing in the shallower regions of the soil. Sandy soils usually allow for rapid water infiltration and drainage; so much so that a significant amount of water can be lost down through the soil and unavailable to grass roots. Hence, for lawns growing on sandier soils a couple of ½ inch applications of water during the week may be more beneficial to the grass plants and less wasteful of the water applied. If you’re uncertain about how much water your sprinkler or sprinkler system is putting out, place a few flat bottom cans (tuna fish cans work well) in the water distribution area of the sprinkler. Leave the sprinkler on for about an hour or one cycle of an automated system then go measure the amount of water in the bottom of the can. That will give you the rate at which water is being applied either through a manual or automated system.

Since spring is a very active period of grass growth, there is greater demand for nutrients, particularly nitrogen (N), to sustain that growth. However, it is equally important to not be over zealous with the application of lawn fertilizers, especially N, in the spring. Remember that most of the growth emphasis of mature grass shoots (which will be most of the lawn) is to produce a flowering stem and then die. Most of us see little of the actual grass flowers because we are always mowing them off. Nonetheless, a light application of nitrogen fertilizer can be beneficial. In most cases this means about ¾ to 1.0 pound of actual N per application. If possible, about half the fertilizer should contain ‘slow release’ nitrogen along with some that is readily available. Once water is applied, the nutrients dissolve and move into the soil where they can be taken up by the grass roots. The slow release fraction provides an additional supply of N over a longer period of time. Very high application rates of nitrogen fertilizers can cause too much top growth at the expense of root growth. Weakened and stressed root systems are less able to supply shoots with the necessary nutrients and water creating even more stress in the grass plant. This also sets up the plant to be even more vulnerable to injury from mid-summer heat and drought stresses likely to come.

If you have been mowing your lawn a little shorter during the early spring period, now is the time to increase mowing heights prior to the onset of summer stresses. This helps encourage a more robust and deeper root system allowing the plant to access a greater volume of soil and therefore larger soil water and nutrient reserves. Higher mowing heights in combination with good turfgrass density can sufficiently shade the soil surface such that weed seeds won’t receive the necessary sunlight to begin germination. Even though other factors such as moisture and nutrients may be favorable for weeds to grow, the reduced sunlight prevents those seeds from germinating and beginning to grow. Mowing should follow the “1/3” rule which states that no more than 1/3 of the turfgrass height be removed at any one mowing. Since growing back that 1/3 will take more time at a higher height of cut, mowing frequency can also be reduced. In other words, if the desired mowing height is two inches, it will take longer for a grass plant to grow from 2 inches to 3 inches, than it will from a mowing height of 1.0 inch to 1.5 inches; both of which are increases of 1/3 in grass plant height.

While there are many other competing interests in the yard and garden during this time of year, regular attention to basic lawn care should still allow ample time for the flower and vegetable garden activities that many of us also enjoy.

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Whether you are looking for tomato transplants, annuals for a front garden bed or a new tree or shrub, one of the most important things you can do to ensure the future success of the plant is to start out with a healthy disease free plant.

Some plant pathogens live in our gardens in plant debris or soil, waiting for the right plant and the right environmental conditions to come along. Other plant pathogens come into the garden on wind, rain, or are carried by insects. Unfortunately many plant pathogens can be brought into the garden on infected plant material.

This later group of plant pathogens can be avoided by a disease management strategy known as exclusion. Exclusion is a strict ‘no pests allowed’ policy. For gardeners, this is one of the simplest pest management strategies to implement.

First, purchase plants from a reputable nursery or seed company. In Minnesota, the Nursery Law (MN statutes, Chapter 18H) protects consumers, by requiring that all perennial nursery plants be inspected annually and certified pest free before being sold. This includes perennial flowering plants, trees, shrubs and other perennial landscape plants. Anyone selling perennial nursery plants in Minnesota must have a nursery certificate. You can verify any vendor’s certificate status at the Minnesota Department of Agriculture’s website.
Although you may find a great deal on plants on e-bay, Craig’s list or at a garage sale, remember these plants have not been inspected and many gardeners have found that their bargain plant came with a free plant pathogen. These unwanted pathogens can harm the new plant and potentially spread to other established plants in the garden.

At the nursery or garden center, carefully inspect every plant prior to purchase. Look at the upper and lower leaf surfaces for spots, discoloration, unusual growth or other signs of disease. Examine the stem. Are there any open wounds, excessive sap, discolored or soft mushy areas? These could all indicate a disease problem. Either in the store or prior to planting, examine the roots. They should be firm and light colored. Dark mushy areas may be infected with a root rotting pathogen. Reject any plants showing symptoms of disease. If many plants in a group appear diseased, do not purchase any of the plants within the group. Nursery plants are often grown close together and share many maintenance practices like pruning, watering and fertilizing. If there are infected plants within a group, it is easy for the plant pathogen to move from one plant to another in a nursery setting.

Read over the plant tag. Is this plant hardy in your area? Will the plant thrive in the conditions of your garden? Plants stressed by cold, drought, too much sun or shade or other environmental problems often are more susceptible to disease problems in addition to environmental stress.

Whenever possible purchase plants that are bred to be disease resistant. Many common disease problems like apple scab on crab apple, powdery mildew on phlox and Verticillium wilt on tomato can be avoided altogether by growing disease resistant varieties. Disease resistance is often listed on the plant label.

In addition, some plants like roses and hostas are screened by some nurseries to verify that they are free of viruses like Rose Mosaic Virus and Hosta Virus X. Ask at the nursery if these plants have been screened or ‘indexed’ for virus prior to purchase.

Careful selection of plants early in the season can help gardeners avoid future disease problems.

Splitting and sharing perennial plants is a tradition as old as gardening itself and can be a cost effective way to grow your garden while connecting to friends in the gardening community. If you are receiving plants from a split perennial, accept plants from someone you know and trust. Volunteer to help dig and split plants. This will allow you to see the mother plant. Select vigorously growing plants for division. Examine the plant carefully for any disease signs or symptoms. Look for spots, discoloration, unusual growth, or rot on all plant parts. Reject plants that appear to be infected with a disease. Healthy looking, vigorously growing plants can be split and shared. Gardeners may choose to take extra precautions against introducing a disease problem by isolating the new plant in an area away from the main garden bed for a year to watch for potential problems. This way, if a problem does come up, the plant is easily removed and it is less likely to spread to your other well established perennials.

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Flea beetles are active on crucifers now. These insects are about 1/16 - 1/8 inch long and an iridescent black violet (flea beetles on other plants are the same size and can vary in color). They overwinter as adults and are active in the spring, feeding on the leaves. They chew small, shallow pits and holes into the leaves. A heavily infested plant looks like it got shot with a BB gun.

Plants are most susceptible to damage in spring - seedlings are more vulnerable than transplants. If your plants are suffering 10 % - 30 % damage, you should treat plants to protect them from flea beetle damage. Apply a garden insecticide, such as permethrin, spinosad, or carbaryl. Different flea beetle species also attack potatoes, spinach, beans, squash, corn, and other plants so be on the watch for feeding injury on these plants as well. More information on flea beetles is available at this link (http://www.extension.umn.edu/distribution/horticulture/M1210.html).

An interesting insect was found on rhubarb recently. At first glance, this very small (1/16th inch long), orange insect appeared to be an aphid. However upon closer inspection, the insects were quite mobile and apparently not feeding. The shape was also not quite right, this insect was more globular than the typical pear-shape you find with aphids. In fact the insect we found was a springtail, more specifically a sminthurid springtail.

Springtails are an extremely abundant group of insects but because of their small size and the fact they are most common in the soil and leaf litter, they are infrequently noticed by people. Springtails are considered beneficial insects because they feed on decaying plant material, helping in the decomposing process. However, infrequently they are found on plants and can actually be found chewing on them. No damage was found on the rhubarb that was inspected. At worst we would not expect anything more than minor feeding. Management for springtails is not necessary.

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A couple of caterpillars were noticed recently. Eastern tent caterpillar is a common insect on apple, crab apple, cherry, and other fruit trees. They have a dark colored, hairy body with a yellow stripe down their back and grow to almost 2 inches in length. They overwinter as eggs on branches and emerge in the early spring. They construct webbing in the forks of branches which is where they rest at night and during cloudy, rainy days.

Cankerworms have also just emerged recently. A type of inchworm, they are yellowish green with a smooth body and grow up to 1 inch long. Cankerworms skeletonize leaves, i.e. they feed between the major veins. When they first start to attack leaves, this damage will begin as small oval holes between veins. As the caterpillars become larger, entire areas between the veins are consumed. Cankerworms feed on a variety of trees, including apple, linden, elm, ash, and hackberry.

Mature, healthy, well established trees can tolerate caterpillar feeding, even when it is severe. Young trees or those that are stressed are less able to tolerate feeding and should be protected from caterpillars. A non-chemical method to eliminate eastern tent caterpillars is to wait until they have retreated to their webbing and then pull the webbing out along with the caterpillars. You can then destroy them by crushing or burning them. You can also treat the leaves with a variety of insecticides. Less toxic choices include Bacillus thuringiensis, insecticidal soap, and spinosad.

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We are well into the beginning of tick season. There are two ticks that are of particular importance to people, the American dog tick, commonly called wood tick, and blacklegged tick, formerly called deer tick. Both ticks commonly bite humans. However while the American dog tick is basically just a nuisance and essentially does not transmit disease to people, the blacklegged tick is a known vector of Lyme disease as well as human anaplasmosis (formerly known as human granulocytic ehrlichiosis) and babesiosis.

Both ticks are found in hardwood forests and fields and other grassy, weedy areas, especially along trails and paths. If you are out in areas where ticks are found, take the proper precautions to avoid them. Stick to trails when you are walking and try to avoid moving through grassy areas. Wear protective clothing, such as long-sleeved shirts and pants. You can maximize your protection by tucking your pants into your socks.

Use a repellant for the most effective protection. Products that contain DEET (N,N-diethyl-meta-toluamide) can be applied to your clothes and exposed skin. It is not necessary to use high concentrations of DEET — there is no evidence that increased percentages are more effective. Do not use products containing more than 15% DEET on children. Another effective repellent is permethrin. Apply this repellent only to clothing. Do not overapply any repellent!

Lastly, be sure to check yourself for ticks after you have been outside in areas where ticks occur so you can promptly remove them. This is particularly important because of the risk of disease. Remember if a tick is on you but is not attached and biting, it can not transmit disease to you. Also, there is only one tick, blacklegged ticks, that can transmit disease. They not only need to be biting but they need to be attached for about 36 hours to be able to pass on disease organisms. The more quickly you discover and remove ticks, the lower your risk for contracting disease. Because ticks can be challenging to identify, be sure to have unknown ticks identified by an expert.

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Three picnic shelters at the Minnesota Landscape Arboretum are in the beginning phase of a transformation as the arboretum prepares for its 2009 summer exhibition called Waterosity.  When complete, the picnic shelters will be a new permanent display called Harvest Your Rain.  Each shelter is being modified to show three different ways of managing stormwater runoff from your property’s impervious surfaces such as rooftops, driveways, and sidewalks.  During rain storms and snow melt, rain barrels, rain gardens, and green roofs all “harvest your rain” decreasing the amount of runoff and non-point pollution that would otherwise pour over these impervious surfaces and into sewers and adjoining water bodies such as lakes, rivers, and wetlands.  Below are articles on rain gardens and rain barrels.  In June look for more Waterosity-related articles on green roofs, the new Cutting Edge on Lawns display at the Minnesota Landscape Arboretum, porous paving, and water-wise irrigation tips.

Rain Barrels: A Way of Collecting and using Rainwater

Have you ever watched a river of rainwater run down your driveway into the lake or storm sewer? Or even worse, seep into your basement? Collecting roof runoff in rain barrels is a good solution to these problems and it also helps alleviate stressed water systems and conserve limited resources. Although rain barrels have been around for thousands of years, people are now encouraged more than ever to use them as a way to protect our lakes and rivers while saving money on water bills.

For the rest of the article on rain barrels please see: www.extension.umn.edu/environment/00023.pdf

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Whether you live in the city or reside on a lake or river shore, managing stormwater runoff is worth considering for your landscape. Rooftops, roads, driveways and sidewalks create hard impervious surfaces which rainwater and melting snow cannot penetrate through to soak into the soil. Additional runoff created by impervious surfaces often is channeled into depressions on your property, often eroding soil along the way. The additional runoff also increases the amount of nutrients and sediment that are carried into lakes, rivers, and wetlands.

Simply put, a rain garden is a shallow depression filled with plants designed to collect rainwater runoff and allow it to filter into the soil, removing nutrients, sediments and other pollutants before reaching the groundwater. Small shrubs, flowering plants and ornamental grasses within a rain garden absorb nutrients, and the sediments settle to the bottom. Rain gardens add beauty to the landscape and may attract butterflies and birds.

Rain garden designs can be simple or elaborate, depending on your gardening interest and experience. When designing a rain garden consider placement, soil type, size, desired shape, and plant species. To insure satisfaction, sketch a design before you start.

Rain Garden Placement

Rain gardens should be placed 10’ or more away from buildings to prevent water from the rain garden from entering basements and damaging foundations. They should also be 35’ or more from septic system drain fields, 50’ or more from drinking water wells and well away from underground utility lines. Call Digger’s Hotline (800) 242-8511to locate electrical, gas or telephone lines before designing your rain garden.

Test Your Soil

Of utmost importance is the soil in which a rain garden is constructed. The purpose of rain gardens is to infiltrate runoff water, so the soils need to be porous enough to quickly soak up water, ideally emptying within 48 hours. Forty-eight hours is the standard because most plants can survive inundation for this amount of time and it prevents a rain garden from becoming a mosquito breeding area. A simple test of a soil’s ability to infiltrate water is to dig a wide hole 10” deep and fill it with water; if the water disappears within 48 hours, the site is suitable for a rain garden. For clay soils mix in organic matter before planting.

Rain arden Size and Shape

Often several rain gardens are designed into the home landscape. For roof top runoff each down spout usually drains to one rain garden. Each rain garden should be about one-third the size of the roof area being drained. Rain gardens typically range from 100 to 300 square feet in size. Applying these same concepts, rain gardens may be built to capture runoff from other impervious surfaces such as driveways and sidewalks.

Rain gardens can be designed in any shape - crescent or kidney shapes are attractive. A long and narrow rain garden may be better suited to fitting between closely spaced buildings, sidewalks and roads.

Select Plants

Choose plants that are suitable for your soil type and will tolerate standing water for up to 48 hours. Many native plant species are well suited for rain gardens. If locating a rain garden near a lakeshore or riverbank it is recommended to use native plants, it may even be a requirement, so be sure to check with your local Soil and Water Conservation District or County Environmental Department.

Install the Rain Garden

Once the size, shape and location of the rain garden have been decided, construction can begin. Lay out a rope or garden hose in the shape desired as a guide for digging. On a slope the soil from digging may be used to create a berm on the downhill side of the rain garden. Otherwise, excess soil should be removed from the site. The depth of the depression may vary from 4” to 8”. For best infiltration the bottom of the rain garden should be flat and level. Finally, use plastic pipes, installed above or below ground, or a rock lined spillway to connect a downspout or other source of runoff to your rain garden.  

For more information:
Downloadable “how to” manual by the University of Wisconsin Extension: http://learningstore.uwex.edu/pdf/GWQ037.pdf

Blue Thumb: http://www.bluethumb.org

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Happy gardening!

David C. Zlesak, Ph.D.
Editor
Extension Educator