Weeds and weed control

By Jennifer Fishburn, horticulture educator, University of Illinois Extension

[July 03, 2013]  This weekend, in between the rain showers, I finally had the opportunity to tend to my flower beds. While not the most enjoyable outdoor task, weeding is necessary. Remember the saying, "One year of seeds equals seven years of weeds." That is enough motivation for me to pull weeds in this heat, humidity and mud.

A weed is defined as "a plant out of place." Weeds compete with desirable plants for light, nutrients, space and water. Weeds also harbor insects (mosquitoes) and diseases. It is critical, especially at this time of year, to control weeds in the garden.

There are many weeds that develop at this time of year. Some of the kinds I had the pleasure of pulling were smartweed, lamb's-quarters, foxtail and red root pigweed. What gardeners dread and these weeds have in common are that they grow rapidly, flower quickly and produce thousands of seeds.

Proper identification of a weed and understanding its growth cycle are necessary to its control. It is helpful to know if the weed is an annual, biennial or perennial. Annual weeds, which include crabgrass, smartweed, foxtail, buttonweed and lamb's-quarters, come back from seed each year. Biennial weeds live two years, producing seed the second year. Burdock is one example of a biennial weed. Perennial weeds come back year after year from the same root. Dandelions, quack grass and creeping Charlie are dreaded examples of perennial weeds.

Weed control options include mulching, herbicides and the not-so-favorite hand pulling.

Mulch. Mulching is my favorite option for weed control. Mulches help to suppress seed germination, conserve soil moisture and keep the soil temperature more even. In vegetable gardens, mulch keeps the fruits off the ground. Most plants will benefit from a 2- to 3-inch layer of mulch applied around the plant. To avoid crown rot, keep mulch away from the base of a plant. Mulches control weeds by preventing light, which is needed for germination, from reaching the soil surface. Mulches can be organic or inorganic. Organic mulches include compost, shredded leaves, wood chips, dry grass clippings, newspaper and pine needles. Inorganic mulches include fabric weed barrier, black plastic and rock.

Ground covers. Bare patches of soil will invite weed seed germination, especially in sunny spots. To prevent weeds from taking over a bare soil area, plant a ground cover such as hosta or vinca in a shady area or a thyme or low-growing sedum in full sun.

Hand removal. This method of weed removal includes hoeing, tilling, mowing and hand pulling with a tool such as a garden knife. Cut off weeds just below the soil surface with a sharp hoe. Desirable plants roots are just below the soil surface and can be easily damaged. Ideal between vegetable garden rows (provided you have left ample space between rows) is shallow cultivation with a rotary tiller or manual-powered rotary cultivator. One rule of thumb: Weeds are easiest to remove when the soil is moist but not muddy. Hand removal is easy if you start when the weeds are small and tackle one small area at a time.

Herbicides. Pre-emergent herbicides keep the seed from emerging through the soil. A common pre-emergent herbicide for the home garden is trifluralin, sold as Preen. Post-emergent herbicides control a weed after it has emerged from the soil. 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. Herbicide usage is not recommended in vegetable gardens.

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

For more information on weed identification and control of common weeds, visit University of Illinois searchable websites at http://weeds.cropsci.illinois.edu/weedid.htm.

[By JENNIFER FISHBURN, horticulture educator, University of Illinois Extension, Logan-Menard-Sangamon Unit]