August 18, 2004 at 4:15 p.m.
The stalk borers have a very broad host range, attacking over 200 species including vegetables such as tomatoes, peppers, potatoes, corn, eggplant, asparagus and beans. They also attack perennials including lilies, anemones, canna lilies, carnations, cosmos, daisies, gladiola, hollyhocks, iris, peonies, phlox and purple coneflower. Borers also attack fruits, such as currants, strawberries, gooseberries and cantaloupe. They have been known to attack grain crops and will even infest twigs of some trees.
Weeds are also attacked by the borers, even ragweed, goldenrod, lambs quarters and thistle. In other words, stalk borers will attack almost any plant.
The borers over winter as eggs on plant stems, or on the ground on fallen leaves. They will hatch sometime in May and usually attack grass stems first.
As the borers become older and larger, they outgrow the plant they are infesting and move at night to bore into a larger stemmed plants. During their larval stage, borers will move several times, depending on the availability of food. Stalk borers are aggressive and cannibalistic, so you will rarely find more than one larva per plant.
The larvae are a little over one inch long when fully developed. When they are fully grown, stalk borers have an orange head with most of the body being chocolate brown. There is a white stripe that runs over the top of the body from the head to the end of the abdomen, with another white stripe running along the sides of the body from the middle to end of the abdomen. A couple of short white stripes run on the side of the body near the head. Stalk borers' bodies are smooth with only a few hairs. The larva feed for two to three months before moving into the soil to pupate. They remain as pupae for about three weeks before emerging sometime in September as adult moths. The adults will lay eggs primarily in the folds and creases of grasses, where they will remain until the following spring. There is only one generation per year.
The first sign that you have stalk borers is wilting leaves. Sometimes, the plant may break off, especially after a strong wind. You may also see small holes where they entered the stalk. When you cut the stem, you'll find it is hollowed out, and possibly may even see the culprit still there.
Younger plants are killed when attacked by stalk borer. By the time you notice the problem, it is too late to save the plant, in most cases. Your best bet is to remove the plant and kill the borer, so they don't move to another plant.
Problems are most likely to occur in gardens next to weedy areas. Control weeds to help reduce the risk of infestation. If that isn't possible, keep the grass or weeds cut short, especially in the spring when the borers are looking for feeding sites as well as during the summer when the adults are laying eggs. Insecticides are not recommended as a treatment, since the problems are too sporadic, which makes it difficult (if not impossible) to predict which plant will be attacked, and when.
There are three remote drop off sites for samples in the county: Mannions Greenhouse and Floral in Rush City, North Branch Floral and Federated Coop (Cenex) on Highway 8 in Chisago City. There will not be a Master Gardener on site, but these businesses have agreed to hold the samples for pickup. There will be Master Gardeners on site to answer your questions Thursday evenings from 6-8 p.m. at the Chisago County Hazardous Waste facility in North Branch.
The Lindstrom Farmers Market is now open. There is a Master Gardener there from 8 a.m.-noon every Saturday.
Other ways to access information: www.extension.umn.edu/county/chisago Check out the “Hot Topics” box in the middle of the page for current Chisago County Master Gardener news and events.
You can also click on “Ask a Master Gardener” next to the cute little flower on the right hand side of the page. Here you can search 1000s of answers from Master Gardeners around the state. If you don’t find your answer you can submit a question online or search for University publications.
Bell Museum of Natural History ? For information about snakes, skunks, raccoons or other wildlife around your yard, call the wildlife information line at (612) 624-1374 or www.bellmuseum.org.
Master Gardener voice mail is 651-237-3080, leave a message and a Master Gardener will call you back within a couple of days.
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