Research Update

Practice safe management Where should I look for information on environmentally safe horticulture, especially the use of pesticides on golf courses?-Address unknown (via the internet)

If you really want to take an honest look at pesticide issues, be careful to whom you listen. Much of the information available to the public is misleading and comes from activists who openly admit that their aim is to eliminate pesticides. This makes them less-than-credible sources. A useful discussion of environmental issues as they pertain to golf courses-and one that relies on scientific research-is found in Golf Course Management & Construction: Environmental Issues (Lewis Publishers, Chelsea, Mich.), edited by James C. Balogh and William J. Walker. This reference is available through the U.S. Golf Association. You can order it by calling the USGA at (800) 336-4446.

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The core of the matter I have a customer with 1 to 2 inches of thatch in his lawn. I am recommending dethatching and slice-seeding. But I have always wondered if I also should core-aerate when I seed.-Ohio (via the internet)

Core aeration definitely aids seedling establishment by creating voids in the existing turf stand. This reduces competition for seedlings that germinate in those spots. However, this practice is most often used on golf courses for specific purposes, such as variety conversions on greens.

For residential lawns, dethatching with a vertical mower or a power rake satisfactorily accomplishes similar goals: thinning the turf (which aids seedlings by opening up the turf canopy) and reducing the thatch layer (thatch layers can cause significant problems for seedlings). It also exposes the soil surface, creating favorable sites for seedlings to germinate. Slit-seeding further increases seed-to-soil contact, which is critical for seedling establishment. Achieving these objectives should result in adequate seedling establishment, provided other factors such as moisture and fertility are favorable. Therefore, core aeration isn't really necessary and could even result in a tufted, non-uniform appearance if seeds become concentrated in the aeration holes.

Many operators simply vertical mow, overseed and then make one more pass with the vertical mower to ensure good seed-to-soil contact, rather than slit-seeding.

COMBATING disease with cultivar resistance Plant diseases will always be a problem for landscapes and, therefore, so will the need for chemical and cultural control strategies. However, innate resistance to pathogens has long been recognized as the most desirable approach to disease control. The trouble is that you can't always locate varieties with the desired resistance traits.

Dutch elm disease (DED) is one example. Researchers have long sought resistant American elms, but progress has been slow. As a result, this otherwise-desirable species has long been absent from lists of recommended tree species, and researchers were forced to rely on long-term breeding projects. Finally, however, breeding programs are yielding cultivars with the admired traits of the American elm as well as resistance to DED.

Since 1984, The Elm Research Institute (Harrisville, N.H.) has distributed the 'Liberty' elm, a true American elm with DED resistance. More recently, the U.S. National Arboretum has released the 'Valley Forge' elm, one of several DED-resistant hybrid elms they've developed. 'Valley Forge' is similar in appearance to the American elm and exhibits no susceptibility to DED. The 'Accolade' elm, developed at the Morton Arboretum (Lisle, Ill.), is another recently released elm and resists the beetles that vector DED.

Other approaches to DED are gaining attention, too. A British researcher currently is working with "d-factors"-small, virus-like particles that kill the DED fungus and could provide a viable biological control for the disease. Dutch Trig, essentially a tree-injected vaccine, was developed by Dutch scientists. Researchers are testing it in the United States and, though not yet approved for commercial distribution, it could be available as early as next year. Treatments such as these offer hope for preserving the remaining stands of mature American elm.

The tide also may be turning on a different, more-recent epidemic. Dogwood anthracnose, first described in the United States in 1980, has reduced the popularity of flowering dogwood (both Cornus florida and C. nuttallii) in many areas of the country because of the rapid spread of this often-lethal disease. Until recently, resistant trees eluded researchers. However, in 1990 a group of Tennessee researchers located a few such individuals growing in native forest in Maryland. After successful disease-resistance trials, the researchers and propagators are readying 'Appalachian Spring' for release. This cultivar is not absolutely immune to dogwood anthracnose and may show foliar symptoms. However, under heavy disease pressure, it survives while virtually all other varieties perish. 'Appalachian Spring' is still a few years from public availability but offers hope of restoring interest in flowering dogwood-long one of our most attractive flowering trees.

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