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Vol. 19, No. 2, May 7, 2004 In
this Issue Next issue May 14 |
Black walnut and allelopathy |
Every so often I get a call or an e-mail asking, "What can I plant near my black walnut?" or, "We just took out a black walnut in our yard, can I plant anything in that spot?" Black walnut trees are one of the best-known examples of plants that produce allelopathic chemicals. These are compounds that are toxic to other plants when their roots contact them or may inhibit the germination of seeds of other plants. This is an adaptive trait that allows plants to colonize an area and out-compete their neighbors for space. Black walnut trees produce a compound called juglone, which was named for the walnut genus Juglans. Other members of the genus such as Persian walnuts and butternut produce juglone, but not in the quantities of black walnut. Juglone occurs throughout the tree, but concentrations are highest in nut husks and roots. The compound is poorly soluble in water and may not leach readily from the soil. Therefore, the soil zone around a black walnut may not be suitable for certain plants for up to five years after the tree has been removed. Although there is some disagreement as to whether walnut leaves should be composted, some reports indicate most of the juglone is leached out of composted leaves in about six months. Avoid composting the nut hulls, which are high in juglone. Gardeners and homeowners often observe that many
garden and landscape plants will not grow near walnut trees, while
others are relatively unaffected. While it is clear that plants
vary in tolerance or susceptibility to juglone, most of this information
is observational rather than based on systematic investigation.
For example, thin grass under a black walnut may be due to shading
rather than allelopathy. Here is a brief list of common plants and
their observed tolerance to growing near black walnut trees. A more
complete list may be found on the Internet at: Observed to be tolerant
Observed to be susceptible
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Managing fire blight in the nursery |
Fire blight, caused by the bacterium Erwinia amylovora, can be a serious disease in nursery production of woody plants. Recent frosts and heavy winds injured succulent new growth on material in some nurseries, making them more susceptible to infection. Fire blight can affect the following plants: cotoneaster, flowering crabapple, flowering pear, hawthorn, photinia, pyracantha and mountainash. In the nursery, the pathogen is commonly spread by insects and splashing rain or irrigation. Infected plants have a scorched appearance with young shoots wilting and turning brown. The shepherd-crook shaped dead tips are a good diagnostic symptom of this disease. Samples of live, symptomatic tissue can be submitted to Diagnostic Services at MSU for confirmation. The disease is favored by excessive nitrogen fertilizing and heavy pruning, which both lead to more succulent growth on nursery plants. Tolerant or resistant cultivars of some the above-mentioned plants are available. Results of studies on resistant species across the United States are inconsistent, therefore, nursery growers need to do some cultivar evaluations to determine the best ones for their area. To manage this disease in the nursery "sanitation" is the best strategy. If your nursery is located near old pear, apple or quince trees, these abandoned trees can be a reservoir for the inoculum. Consider removing them. Copper-based bactericides like Phyton or Kocide may be helpful. These materials limit the amount of bacteria on the plant surface but should not be relied upon as the sole management strategy. Where low levels of infection occur the infected tissue should be pruned out. Make pruning cuts several inches below the edge of the infected area. If pruning is not possible, affected plants should be removed from the nursery and destroyed. Sterilize pruning tools/shears between cuts with either 10 percent household bleach or 70 percent alcohol. |
Species diversity in turf |
Depending on your perspective, species diversity in your turf may be OK or may cause you to look for various elimination strategies to clean up the turf. It just depends if you relate to that TV commercial that has people spinning around in a circle in their lawn and claiming how Uncle Bob is a good human being for not having crabgrass in his lawn. Don't get me wrong, there's nothing wrong with that perspective, but I think that in most cases when it comes to home lawn appearance there is nothing wrong with you if there is an occasional dandelion adding a little color to your front lawn. No matter your perspective, here's some musings on species diversity in turf and control tactics if you're an eliminator. Tall fescue If you want to get rid of these clumps of fescue there are a couple choices. Since the tall fescue is usually in very distinct clumps, it is possible to simple dig/cut it out of the bluegrass and then reseed the area. A non-selective herbicide such as RoundUp could also be used, but even after death occurs you're still going to have to dig up the area to make it receptive to reseeding. Dandelions make an appearance An occasional dandelion here and there in the lawn does not justify a blanket herbicide application to the entire area. Spot spray or get down on your hands and knees and pull them out. If pulling is your gig, make sure to get that taproot or else you'll just be pulling again. Now that we've passed the first big flush of dandelions, the second flush is just around the corner. Applications made at that time should yield good results. Most commercially available three-way ready to use herbicides - you know the ones you get in the convenient hand spray bottles - will provide effective control of dandelion. "Other" weeds |
Gypsy moth is now in the process of egg hatch and dispersal in the Lower Peninsula |
You should have received your initial gypsy moth materials from the Michigan Department of Agriculture. If you have not received this information, call your regional office. Spray
windows The Upper Peninsula will be evaluated in one week, at which time there will be a determination of the pest's rate of development. Announcement of the opening of the spray window for the Upper Peninsula will be made at a later date. Growers are advised to use adequate volume and methods to obtain optimum spray coverage of plant material. Proper application of any product is essential for control to be effective. Remember, Dimilin is effective only on early instars of the gypsy moth caterpillars. Since gypsy moth development will vary by location, you will need to monitor development around your farm. Weather conditions will affect caterpillar development and the end date of the spray window. |
Insects to be on the lookout for in Christmas trees |
In the Upper Peninsula, growers can still treat for Christmas tree early insects such as Zimmerman pine moth on Scotch pine, white pine weevil on spruce, white pine and Scotch pine. In the Northern Lower part of Michigan, insects such as balsam twig aphid on balsam and Fraser fir, Cooley spruce gall adelgid on spruce and Douglas-fir and eastern spruce gall adelgid on white and Norway spruce can be found. In the Southern Lower Peninsula, look for pine needle scale and Jack pine budworm on Scotch pine, and pine root collar weevil adults on Scotch and red pine. Cooley's and Eastern spruce gall adelgids are the sap-feeding insects that cause galls to form on the shoots of Colorado blue spruce (Cooley's adelgid) and white spruce (Eastern adelgid). Time is running out if you need to control Cooley spruce gall adelgid or eastern spruce gall adelgids on your trees. If you had lots of galls on your spruce trees last year, the best time to apply an insecticide is when the buds are swollen, and the buds have not broken. New galls usually appear around 200 to 300 GDD50. Once the new galls are present, insecticides will not be effective. Make sure you get good coverage - these adelgids are very small. Cooley spruce gall adelgids also feed on Douglas fir needles. They do not cause galls to form on Douglas fir, but they do cause the needles to become distorted, and at high densities, will reduce needle and shoot growth. You will usually find the adelgids on the undersides of the needles. They look like tiny, white cotton balls on the needles because the adelgids secrete white, waxy material as they feed. One stage of adelgid eggs often hatch in the spring, soon after buds break. The new nymphs will move onto the tender, succulent young needles. It often looks like someone has sprinkled black pepper on the new needles. If you need to apply an insecticide, this is a good time to do it. Keep an eye out for pine needle scale crawlers. They should be hatching any time now, in the southern half of the Lower Peninsula. This usually happens around the time that lilacs are at full bloom. Look for the tiny, red crawlers moving about on the needles. If populations are high and you plan to sell the trees within one to two years, you can apply a horticultural oil (2%) or an insecticide. The best time to spray trees is after all the eggs have hatched, and the crawlers have begun feeding. Once the crawlers insert their mouth into the needles and start to feed, they cease to move around. They go from a red color to a pinkish-opaque, almost yellow color, but they have not yet started to produce the hard white armor. This is called the hyaline stage and this is the best time to control the scales with a spray. On the other hand.be real sure that applying a spray is necessary. Look closely at the white scales on the needles. Do you see lots of scales with a round hole or a hole with jagged edges? That is evidence that parasitoids (round holes) and predators (jagged holes) have attacked the scales. You can also check to see if there are viable eggs below the hard white scale armor. Carefully flip off the white armor and see if you see the little reddish eggs. If you don't find eggs under most scales, then you may not need to worry about spraying. There's an even easier way to check out egg viability, too. Clip off some shoots heavily loaded up with white scales from a few trees. Put a white sheet of paper into a plastic bag, and then put the infested shoot into the bag. Leave the bagged shoots inside. If there are viable eggs under the scales, they will hatch very soon and you will see the red crawlers moving about on the white paper. For pine shoot beetle, destroy cull trees by May 20. Don't forget, if you are in the Pine Shoot Beetle Compliance Program, you must have your trap logs and piles of cull trees collected and destroyed by May 20. Also be sure your stumps are cut low or sprayed to prevent any new beetles from completing development and emerging. |
Clover mites and solitary bees: It's a matter of turf |
Problems with ground-nesting solitary bees and clover mites are often related to lawn problems. Solitary bees dig their nest burrows in areas of the lawn where the turf is sparse. Clover mite invasions into homes usually occur when lawns are planted right up to the foundation of the house. Both problems can be managed, if not eliminated, by making some adjustments to the lawn. Clover mites, Bryobia praetiosa, are among the smallest home invaders we have in Michigan. They belong to the spider mite family Tetranychidae and, as the name implies, they feed on clovers and grasses. People often mistake clover mites for minute six-legged insects because their front legs are considerably longer than the others, and they are projected forward giving them the appearance of antennae (mites do not have antennae). Lush growing, well-fertilized lawns tend to produce the largest number of clover mites. For whatever reason, newly established lawns also seem to harbor large numbers of clover mites. When conditions are right, clover mites can invade homes by the thousands. This normally happens in the spring, but fall invasions also occur. They are small enough to crawl right through window screens and through cracks around windows, doors and other external openings. If they are crushed during attempts to wipe them up, they leave tiny red stains. Clover mites are usually a temporary nuisance. They appear suddenly and are generally gone a few days later. Household aerosol insecticides can be used to kill the mites indoors, if deemed necessary, but a soapy rag or wet sponge work just as well on indoor surfaces. A vacuum cleaner equipped with a hose and a soft brush attachment will also work. Wipe or brush carefully to avoid crushing the mites and causing stains. Mites can be removed from the outside of buildings with a garden house. An insecticidal soap can be concocted by using regular liquid dishwashing soap mixed at the rate of two tablespoons per gallon of water. These water-based treatments will not provide any residual control. A more aggressive approach would be a perimeter treatment of a persistent insecticide along the outside walls and extending about 10 feet out from the foundation. Be sure to read and follow all instructions and safety precautions found on the label before using any pesticide. The best long-term method for reducing persistent clover mite invasions is by providing a grass-free band, 18 to 24 inches wide, around the house. This can easily be accomplished by open areas of course sand or pea stone, or by installing a plant bed. Removing clovers and other groundcovers from the lawn may also help prevent mite numbers from building up in lawns. Solitary bees nesting in yards are another problem that has been increasing over the past few years. Their increase may be related to the decline of honeybee populations and they, no doubt, serve an important role as pollinators. There are 100's of species of bees that live in Michigan and the vast majority of these species is solitary. Most belong to the bee families Colletidae, Andrenidae, Halictidae and Megachilidae. Solitary bees construct individual nest tubes each with its own opening. Ground-nesting yellow jackets are social insects, and a colony of several hundred wasps typically uses a single nest opening. Solitary bees range in size from 0.5 to 0.75 inches and come in a variety of colors such as blue, green, copper or metallic red. Females dig nesting tubes during the evening hours that may reach six or more inches in depth. Some species line the tubes with a secretion that helps to protect the nest from moisture. Solitary bees often nest in large congregations with many nesting holes arranged very closely together. The reason for this is not clear. Some suggest that quality nesting sites are in such short supply in urban environments that the bees crowd up when one is located. Or, they may simply like one another's company. During the day, the female bees collect pollen and nectar to carry back to their nest. A single egg is laid on the pollen ball in April and May. After hatching, the larva feeds on the pollen and develops within the tube until it reaches adult stage in the fall. The new adult remains in the tube throughout the winter until it emerges from the ground the following spring. Male bees typically emerge first and ambush the females as they emerge from the opening. Mating takes place, males soon die off (talk about bad karma) and the females resume the nesting cycle. Although these bees feed on nectar, they do not produce honey. Ground nesting bees are reported to prefer nesting in areas with morning sun exposure and well-drained soils. Tunnels are excavated in areas of bare ground or sparse vegetation. Damage to lawns and turf is usually minimal but most people I talk to tend to be threatened by the bees and wish to rid their yards of them. Solitary bees rarely sting. Their venom is relatively weak and there is no mass attack one may experience with honeybees and yellowjackets. Outdoor activities, including lawn mowing, can often be continued with no problem. Nesting areas in out of the way locations can simply be avoided for 4-6 weeks while nesting activity is underway. Controlling solitary bees in yards is best accomplished by establishing dense turf in the area(s) that the bees favor. Another cultural method that can be employed is heavy watering or irrigation with a lawn sprinkler during the nest-building period to discourage nesting behavior. If the soil or location will not produce dense turf, then ground covers or heavy mulches will provide an alternative solution. The most aggressive control strategy is using insecticides to kill the bees. If the nest area is small, then Sevin Garden Dust can be applied to nest openings. Larger nest areas may be easier to treat with a small, hand-held sprayer using liquid Sevin or cyfluthrin. Please keep in mind that ground-nesting bees play a vital role in pollination of crops and wild plants. They should be preserved whenever possible. |
Prepare for a cicada invasion |
Some parts of Michigan and surrounding states will have a major hatch of 17-year cicadas in May and June. This year's brood (Brood X) is the largest of the 17-year cicada broods, and encompasses parts of 15 states (including southern counties of Michigan). Entomologists like myself get pretty excited by such occurrences - it's kind of like the Olympics for us, except it's every 17 years. However, given past experience with cicada hatches, the Region 5 EPA Office in Chicago suggests "preparing for the emergency" in case homeowners, businesses and schools "panic." So to prepare you against the panic, here are some web sites for additional information. The University of Michigan site is very good and includes a map for Brood X. University of Michigan: http://www.ummz.lsa.umich.edu/magicicada/Periodical/Index.html Cicada Mania: http://www.dancentury.com/cicada/cicadalinks.html News articles: http://www.freep.com/news/statewire/sw94367_20040311.htm http://www.centredaily.com/mld/centredaily/news/local/8163648.htm |
Climatological last freeze dates |
A common question this time of year in the Agricultural Weather Office is, "When can I expect the last freeze of the season this spring?" Given more than 50 years of climatological data to ponder, the answer statistically is relatively straightforward but depends greatly on your location. Figures 1 and 2 depict the normal and record latest dates of last freezing temperature (32°F or lower) of the spring season, respectively. Most areas of the state experience last freeze during May, although the records indicate that it is possible for many spots to see freezing temperatures well into June. One can see the strong dependence on proximity to the Great Lakes with significantly earlier last freezes in areas near the lakes versus those further inland. Interestingly, the record latest "spring" freeze for the state for this period is at Vanderbilt, on July 30. This station also recorded a freezing minimum temperature on August 2 the same year (1972). Because of this, the defining limits of the last "spring" freeze and first "fall" freeze in Michigan (this could also be interpreted as a two-day growing season!) had to be arbitrarily set at July 31 (with the beginning of the fall as August 1). As is the case in the fall with the first freezing temperatures of the season, it is nearly impossible to project very far in advance when the last spring freeze may occur with any accuracy. Meteorologically, however, at this point in the season, about the only way to experience a widespread frost/freeze in central and southern parts of the state is through the passage of a "Hudson Bay" high-pressure area through the region. These air masses occasionally move southwards from their source region along the western edge of Hudson Bay into the Great Lakes during the spring with a large area of abnormally cold, dry air (dewpoint temperatures typically in the 20's or even teens) on northeasterly winds. This synoptic situation is responsible for the majority of widespread late spring freezes in Michigan. As a result, one can monitor weather maps and forecasts, especially the medium-range forecasts, for any signs of this pattern. For those interested in the absolute earliest freeze, last freeze with a temperature other than 32°F (such as 28°F), or more statistical detail, this information is available on the State Climatologist's web site at: http://climate.geo.msu.edu/ (proceed to "Michigan Map," then click on the desired region followed by the station of interest, which will bring up statistical tables for that station, including last spring freeze information) or by calling or writing the Ag. Weather/State Climatologist's Office (Both have the same phone number, 517-355-0231.). |
Weather news |
Widespread rains fell over much of the state last weekend, complicating spring fieldwork operations but easing abnormally dry conditions across southern sections of the state. In the wake of the precipitation, relatively clear, calm nights, dry air, and strong radiational cooling resulted in widespread frost and freezing temperatures across much of the state on the mornings of May 3 and 4. The first week in May marks the average date(s) of last freezing temperatures of the spring season across many sections of the Lower Peninsula. In western Michigan along the lakeshore it is earlier, in northern interior areas of the state, it is later (See accompanying story on last spring freezes.). Looking ahead, a very active weather pattern is expected across the region into next week. On Saturday (May 8), a warm front will approach Michigan from the south, the next of a series of several frontal passages likely to affect the state during the next several days. This will result in the likelihood of showers and a few thundershowers statewide Friday night into Saturday. For the remainder of the weekend this frontal boundary is expected to waver near Michigan, serving as a focusing mechanism for more periods of showers and thunderstorms. Best chances for rainfall, some of it heavy, will be in southern sections of the state. Temperatures will depend greatly on the exact position of the frontal boundary with daytime readings reaching the 70's and low 80's to the south of the front, with 40's, 50's and 60's to the north. Low temperatures will range from 30's and 40's north to the 40's and 50's in the south. Medium-range forecast guidance is consistent with the emerging weather pattern mentioned above with an upper air trough over the western US (This should bring some relief to those battling wildfires in CA.), and a broad upper air ridge across the central and eastern US. An active storm track is expected on the northern edge of the ridge from the central Great Plains northeastward into the Great Lakes region. For Michigan, both the 6-10 day outlook (covering May 11-15) and 8-14 day outlooks (covering May 14-20) call for near normal temperatures. Precipitation is expected to be above normal state- and region-wide. |