Weed Control

Gardens come in many shapes and sizes but one thing they have in common are weeds. For many gardeners, trying to control weeds is a never-ending struggle.

One reason for controlling weeds is that they spoil the appearance of gardens. Another is that if they are not controlled early, they increase and spread, and are more difficult to control later. Probably the most important reason, yet one that is often overlooked, is that they reduce the growth of neighboring plants, mainly through competition for water and nutrients. Even trees and shrubs, especially during their early years, are sensitive to competition. Because all growing plants remove water and nutrients from the soil, even lawn grasses and ground-cover plants can be considered "weeds" if they are too close to trees and shrubs.

Hand-hoeing is still the best method for the home gardener. It is inexpensive, quite selective, accurate, effective, and for some people, even enjoyable. A great deal of emotional satisfaction can come from leaning on a hoe handle while viewing a clean, freshly?hoed row where weeds grew only minutes before. When hoeing, a fair amount of hand pulling is usually necessary if weeds are growing close to the base of the desirable plants. A fair amount of damage may occur to vegetables if weeds are allowed to get big before being pulled. Other alternatives are mulching and using herbicides.

Mulching controls weeds by keeping light away from seedlings and providing a mechanical barrier to emergence. It works best against weeds that come up from seed each year. Weeds that do come through the mulch are easily spotted for removal and are easily pulled from the moist soil.

Good mulching materials include compost, straw, leaves, hay, sawdust, wood shavings, bark, paper and plastic sheeting. The most popular synthetic material presently in use is 1 and 1-1/2 mil. black polyethylene film. Clear plastic may be unsatisfactory since it allows light to enter, encouraging weed growth under the plastic. Black plastic will heat soils faster. All plastic mulches should be removed when hot summer days begin since they can actually overheat soils. A good source of plastic mulch is garbage bags that have been split on one side so that they cover the planting bed. Plants are planted in holes made in the plastic covered beds. Organic mulches form a barrier which will not allow soil temperatures to change rapidly. This is a benefit in the hot summer since the soil remains cooler but can cause plant injury from frosts in the early spring because there is no release of soil heat.

Herbicides provide new opportunities in weed control. They can prevent weeds from emerging, kill weeds growing near to garden plants and control deep-rooted perennials without disturbing the soil around desirable plants.

One of the available herbicides is glyphosate, sold as Roundup, Kleen-up, Doomsday and Weed?and?Grass Killer. check the label for the term "glyphosate." There are some grasses and weeds, such as bermuda grass and Johnson grass, which resist pulling and hoeing. They actually grow better the more you cut, pull and hoe! When used as directed, glyphosate-containing herbicides effectively control many weeds that other herbicides cannot control, and have no adverse effects on cropping systems or the environment. The "active" ingredient in these herbicides is the isopropylamine (IPA) salt of glyphosate (N?(phosphonomethyl) glycine). The nutrient transport system of the plant is utilized for translocation from the plant foliage to the underground root or rhizome system. Symptoms of activity develop slowly, and weed damage may not be obvious for 4 to 6 days for annual plant species and up to 10 days or longer for perennials. Visible effects are a gradual wilting and yellowing, which advances to complete browning and deterioration of plant tissue.

Glyphosate-containing herbicides are most effective when applied to the foliage of actively growing annual and perennial weeds or brush. Control of perennial weed species is most effective when applications are made at, or beyond, the early head or early bud stage of growth.

Mowing or tillage operations should not be done prior to, or immediately after application, since sufficient time (3 to 7 days) must be allowed for translocation. If weed foliage is removed, it must be allowed to regenerate sufficient size to permit uptake and movement through the plant.

Upon contact with the soil, glyphosate is inactivated. The herbicide is tightly bound by the soil particles, preventing glyphosate uptake from soil by plant roots. This binding also prevents leaching and lateral movement through the soil. When applied to the soil at test rates 30 times the normal use rate, glyphosate-containing herbicides did not affect the growth of crops planted immediately after treatment.

Seeding of crops should be delayed until the treated vegetation dies. The success observed with this delay may be related to: (1) improved soil moisture conditions, (2) insects and soil biota, (e.g., slugs, snails) that feed on emerging seedlings, leaving the dead vegetation, and (3) dissipation of toxic substances produced by some types of dying vegetation. Since glyphosate has no residual soil activity, it will not control weeds that emerge after application.

For maximum weed control with glyphosate-containing herbicides, good application conditions are important. Application is not recommended when winds favor physical drift of spray solution, or when rain is expected within 6 hours. The weed foliage should be dry and free of visible dust cover that could interfere with proper absorption of the herbicide. The formulation is non-volatile and will not damage any plant not contacted during application. If a non-target plant is accidentally sprayed, immediately wash or rinse the foliage with water to avoid uptake and later damage or death.

Proper translocation occurs only in actively growing weeds. Reduced control may result when treated weeds are not actively growing due to stress caused by drought, insect damage or disease. Although extremely cool or cloudy weather may delay visual symptoms of control, weed control is not reduced.

There is a "natural" herbicide that is recommended by some people. Malcolm Beck, founder of Gardenville Products in San Antonio writes: "Corn gluten meal is a high protein that makes it about 10 percent nitrogen. Apply it as you would a fertilizer, about 20 pounds per square feet, to the top of the soil. You may scratch it in lightly, then water enough to sprout seeds and hope it doesn't rain. It needs to stay dry. The seeds sprout, but for some reason the roots do not develop. If your timing is too early for the weed seeds and there was continuous moisture, such as rainy spell, the microbes eat the meal before it can do it's thing to the weed roots, and then you got the healthiest weeds you ever saw. The trick is, knowing when the native weed seeds are about to sprout. Once a root is established, the meal has no effect. This is an excellent fertilizer for perennials such as strawberries, blackberries, lawns and such. This is an organic weed and feed. It is a win, win or just a win situation. Either way you win."

Most annual weeds can be controlled by cultivation! Annual broadleaf weeds are easily removed while they are in the seedling stage. Cultivations should be made to control each flush of weeds that emerges, usually within a few days after a rain. At this time, weed seedlings are easily uprooted even with hand?pushed garden plows, hoes and other hand tools.

If weeds are allowed to get very large before control measures are taken, their root systems will develop to such an extent that removal with a garden plow or hoe will be difficult, if not impossible. The old saying, "nip it in the bud," certainly applies to weed control in the garden.

The first few weeks after vegetables are planted is the most important time to control weeds. After the vegetables get well established and start shading the ground, they become competitive and do a good job of preventing new weeds from becoming established.

By following good cultural practices and using mulches along with the timely cultivations and hand hoeing, most annual weeds can be controlled in home gardens without excessive "back?breaking labor." In fact, if done in time the exercise required to control weeds in home gardens would be beneficial to most of us. If nothing else, it should stimulate our appetites and make us appreciate those delicious vegetables being produced.

No one method of weed control is best for all situations or problems. Personal preference, size of garden and the time available are just some of the factors to be considered.