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Ornamentals and Turf |
Ambrosia beetles never die, or so it seems. Samples with and questions about ambrosia beetles continue to arrive. While it is a bit late to do anything now, Ornamental and Turf Insect Note No. 111 provides a review of their biology and control. Of most concern is that some growers and landscapers continue to use systemic insecticides for ambrosia beetle control, which is completely ineffective and should not be done. Remember that these insects cultivate their own food (the ambrosia fungus) and do not consume plant material.
This week the larvae of the rosy maple moth on maple trees are popular. The greenstriped mapleworm is one of the more common caterpillars on maples although it is usually not a widespread pest. Occasionally greenstriped mapleworms become locally abundant. This may be one of those years. When fully grown, the caterpillars dig into soil to pupate. A few weeks later, the pupae molt into beautiful pink and yellow moths called rosy maple moths. These moths then lay masses of bright yellow eggs from which hatch a second generation of greenstriped mapleworms. Every few decades, these caterpillars become abundant enough to cause significant damage to maples. Because the caterpillars are gregarious, knocking them out of the tree is a viable solution for a small tree. If the foliage is being severely stripped, Sevin or some other contact insecticide should provide adequate control. Bacillus thuringiensis should provide adequate control, especially if it is applied when the mapleworms are small.
Iris borer damage begins in the foliage and you may start to see it now. Most of the time, the evidence of iris borer is its damage to iris rhizomes discovered when people dig the rhizomes to transplant them during the summer. The moths emerge in late summer to mate and lay eggs on the oldest, roughest, dead and bleached iris leaves or on plants nearby. The eggs hatch the following spring. The tiny caterpillars first feed on the new foliage and sometimes cause the margins of the leaves to be ragged. The holes caused by the young caterpillars bleed causing deposits of sap on the leaves. The caterpillars then mine in the leaves for a time before working downward toward the rhizomes. The caterpillars are about half grown by the time they reach the rhizome. There they feed on the edge or on the underside of the rhizome, sometimes boring in. Often a single caterpillar may devour completely the insides of a rhizome before migrating to others. The mature caterpillars are pale yellow/pink to pink in color with brown heads.
To control the iris borer, it is important to remove all old iris leaves and other plant rubbish from the beds in early spring before new growth emerges. If the borers are discovered later in the spring, it may be possible to crush the caterpillars with the thumb and finger inside the leaf. By holding the injured leaf so that the sun shines on the far side, the silhouette of the small caterpillar should be easily visible through the leaf. John Weidhaas at Virginia Tech University has determined that Sevin and malathion give good control of the iris borer when these pesticides are applied early while the caterpillars are feeding on the outside of the leaves (we may be beyond this stage now).
Dimethoate (Cygon 2E) is mostly no longer available for homeowners and Orthene (acephate) is on the way out, though still on shelves. Imidacloprid (Merit 75 WP) is also a systemic and effective insecticide. Studies at the University of Maryland show that entomopathogenic nematodes, Steinernema carpocapsae and Heterorhabditis bacteriophora, were as effective as chemicals against iris borers when applied correctly. Applications were made after soil temperatures reached 50 degrees F. Enough water was applied (1 quart per square foot) to allow nematodes to move in the soil. It helps if the borers are still in the larval stage, which is the most susceptible to the nematodes.
Control measures include sanitation, early pesticide application, destruction of the insects in the mine, and systemic insecticide application.
In the past few weeks I have received several samples of quackgrass for identification. In the past 7 years, I have only once before received a sample of quackgrass for identification. Is it becoming more of a problem? I don't think so, but perhaps there is just more quackgrass being introduced in field grown ornamental plants produced in the northern states.
Quackgrass is a perennial grass with gray to blue-green foliage. It is easily distinguished from other grasses by the presence of clasping auricles and rhizomes. Good photographs of quackgrass are available on the following web site: http://www.agf.gov.bc.ca/cropprot/weedguid/quackg.htm.
Quackgrass is about as difficult to control as bermudagrass. But, in broadleaf ornamentals and conifers it can be selectively controlled with Fusilade II or Envoy. Vantage is less effective. See the article Postemergence Grass Control in Landscapes and Nurseries in the May 14, 2004 issue of the North Carolina Pest News for more information on postemergence control of weedy grasses in landscape plantings.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on June 21, 2004 by Stephen J. Toth, Jr.