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Thursday, July 31, 2003 02:20 pm

W-e-e-d

That four-letter word

art380

Tip of the week

To view the best free garden display in central Illinois, drive through the Illinois State Fairgrounds in the next couple of days.

The other day I almost lost my one-year-old daughter--she had walked into the garden where the weeds were tall. I had to face up to the chore I'd put off for weeks. Who wants to weed in this heat and humidity?

A weed is defined as "a plant out of place," competing with other, desirable plants for light, nutrients, space, and water. It's critical, especially at this time of year, to control weeds in the garden.

Outside my window are lambsquarter, foxtail, and red-root pigweed forming seedheads. These weeds all grow rapidly, flower quickly, and produce thousands of seeds.

Don't let weeds go to seed. One year of seeds can result in several years of weeding. Some seeds may lay dormant in the ground for decades.

Proper identification of a weed is necessary to control it. It helps to know whether the weed is an annual, biennial, or perennial. Annual weeds--which include crabgrass, foxtail, buttonweed, and lambsquarter--come back from seed each year. Biennial weeds live two years, producing seeds the second year. Burdock is a biennial weed. Perennial weeds come back year after year from the same root. Dandelions, quackgrass, and creeping charlie are dreaded examples of perennial weeds.

How to control them? There are several options to consider.

• Mulch. This is my favorite option for weed control. Mulches help to suppress seed germination, conserve soil moisture, and moderate soil temperature. Most plants will benefit from a two- to three-inch layer of mulch. To avoid crown rot, keep it away from the base of the plant. Mulches control weeds by shielding the soil from sunlight, which is needed for germination. Organic mulches include compost, shredded leaves, wood chips, dry grass clippings, newspaper, and pine needles. Inorganic mulches include black plastic and rock.

• Ground covers. Plant ground cover--such as lamium in the shade or a low-growing sedum in full sun--to prevent weeds from taking over bare patches of soil.

• Hand removal. This method of weed removal can also include hoeing, tilling, mowing, and pulling with a garden knife. Cut off weeds just below the soil surface with a sharp hoe. The roots of desirable plants are just below the soil's surface and can be easily damaged. Hand pulling is ideal between vegetable rows (provided you have left ample space between them). One rule of thumb: weeds are easiest to remove when the soil is moist.

Hand removal is easy if you start when the weeds are small and tackle one small area at a time. A friend of mine gardens in three-by-three raised beds. To break up one huge task into smaller ones, she weeds them one at a time. Avoid what I did as a child--wait until the weeds get two feet tall and then try to weed the family's 800-square-foot garden in one day.

• Herbicides. Some can keep the seed from emerging through the soil. A common pre-emergent herbicide for the home garden is trifluralin, sold as Treflan or Preen. Other herbicides take care of weeds that have already seen the light of day. Glyphosate, sold as Roundup or Kleenup, is a nonselective herbicide for controlling perennial weeds. Nonselective means it will kill any plant. To protect your desirable plants, use a foam paintbrush to apply the glyphosate.

When using any chemical, it's important to read and follow all label directions. And pay attention to the appropriate time to apply the chemical or you may have wasted your time and money.

For more information on weed identification and the control of common weeds, check out the University of Illinois' searchable Web site (web.aces.uiuc.edu/weedid/index.html) or Midwestern Turfgrass Weed Identification and Control (www.turf.uiuc.edu/weed_web/index.htm).

Critter of the week

Have you noticed bare branches on trees and shrubs, especially on blue spruces? It's probably due to bagworms.

In the winter you may see two-inch-long silk bags camouflaged by bits of foliage, bark or other debris. The young caterpillars or larvae emerge in June. Bagworms attack a wide range of trees and shrubs, including spruce, arborvitae, juniper, pine, maple, crabapple, and linden.

Recommended insecticides include Bacillus thuringiensis kurstaki (Dipel or Thuricide), cyfluthrin (Tempo), trichlorfon (Dylox), and spinosad (Conserve). Older larvae (three-quarters to one-inch long) consume entire needles or leaves and are more difficult to control. Cyfluthrin and trichlorfon are recommended for larger larvae. Thorough spraying of all plant parts is essential, especially the tops of trees.

Though bagworms are susceptible to natural enemies, including the ichneumon parasitic wasps (Itoplectis conquisitor and Chirotica thryrifopteryx) that attack the pupae, bagworms are generally present at damaging levels before the wasps are effective.

Around mid-August, bagworms will lay eggs. In the fall and winter, hand picking is effective.

For more information on bagworms, visit the Ohio State University on-line fact sheet at ohioline.osu.edu/hyg-fact/2000/2149.ht

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