By Bev Sandlin, Master Gardener Fillmore County
Recently I was sitting at the county fair volunteering with other master gardeners when the subject turned to grass control in bulb flower beds. One of the ladies knew of an herbicide called POAST that kills only grasses! Since I had never heard of such a product, and this fascinated me as a perennial flower gardener. When I looked up Poast on the Web, I ran across this article on weed control in the garden. I think it has a few valuable tips for the beginning gardener and although I prefer a totally organic food garden, it does have a primer on the basic herbicides as well – when all else fails, chemicals are an option.
Weeds (plants growing out of place) are a serious garden problem. They rob vegetable plants of sunlight, water, and nutrients. They also provide hiding places for insects and serve as a source of vegetable diseases.
Weeds can kill a gardener’s enthusiasm, which can cause them to abandon the garden in midsummer. It is important to control weeds while they are small and before they get out of control.
Since any plant growing out of place can be considered a weed, a sweet corn plant (from a carelessly dropped seed) growing in a row of bush snap beans is technically a weed; but the most common garden weeds are crabgrass, yellow and purple nutsedge, morning glories, bermudagrass, and pigweed.
Most weeds can be controlled and kept from becoming serious problems in the garden. Methods of control include hand-pulling, cultivation, mulching, chemicals – and of course the popular and always useful weed eater.
Hand-pulling is not an effective way to control weeds in a large garden, but it can be effective under certain circumstances. Hand-pull weeds that appear in the row with vegetable plants, as well as those that grow in the planting holes of a plastic mulch.
Weeds that grow between closely spaced rows of vegetables in wide rows, raised beds, or small gardens also may require hand-pulling. Weeds growing in containers used for vegetables should be hand-pulled. Extremely small weeds are difficult to pull by hand but do not wait until the weeds get so large that pulling them destroys adjacent vegetable plants. Thinning seedlings spaced too closely together and hand-weeding frequently can be done at the same time.
Cultivation is the most widely used method of garden weed control. It is not a one-time chore, for with each rain, irrigation, and stirring of the soil, weed seedlings emerge.
A variety of hand and power equipment is used for cultivation, but the most commonly used tools are the hoe and garden tiller.
A sharpened hoe blade is an excellent tool for cutting the roots of weeds. The severed plants dry in the sun and die.
A garden tiller and other soil-disturbing tools, the hoe included, are used to disturb the soil around the weed plant’s roots. On a hot day, the weeds die when their roots dry and the plants are unable to get water. Small weeds die more quickly than large weeds, so cultivation should be frequent enough to prevent weed seedlings from becoming established. Cultivation should also be shallow so you do not disturb or injure vegetable plant roots.
Deep cultivation, in addition to destroying weeds, injures vegetable plant roots and brings more weed seeds to the surface, where they germinate. “Hoe blight,” the wilting and death of vegetable plants after cultivation, often results from careless cultivation.
Take a perennial weed, such as bermudagrass, out of the garden following cultivation because pieces of the plant that have no roots can form roots and make the bermudagrass problem worse.
Mulching is an effective way to control garden weeds. Natural and plastic mulches properly applied to weed-free garden soil prevent most weeds from becoming established in the mulched area. Bermudagrass and nutsedge are difficult to control completely with mulches. Weeds that appear in the planting holes of plastic mulch should be pulled by hand.
Commercial vegetable growers have a fairly wide choice of chemical weed killers (herbicides) to prevent or control weed problems. Gardeners, however, have a much smaller choice of herbicides.
Don’t expect to control all weeds in a garden of mixed vegetables with one herbicide. First, no single herbicide controls all weeds. Secondly, some vegetables are also sensitive to the herbicide, and if the wrong herbicide is used, the vegetable is injured along with the weeds.
Herbicides applied to the soil before vegetables are planted and before weeds have emerged are called preemergence herbicides. Some preemergence herbicides can be applied immediately after the vegetable seeds or plants are planted but before the weed seeds germinate. Postemergence herbicides are applied after weeds have emerged.
Herbicides used in the garden may be in the form of granules, wettable powders, or liquids. The equipment needed for application depends on the formulation used. Use a pump-up pressure sprayer for applying liquids and wettable powders. Since most garden sprayers are equipped with a cone-type nozzle, use a 50-mesh screen and a 8003 E or equivalent fan nozzle attached to the sprayer for applying herbicides.
Chemical herbicides used in the vegetable garden can be washed from the sprayer, but some of those used on the lawn cannot. Therefore, a wise gardener will keep two sprayers: one for lawn herbicides and the other for garden herbicides. When spraying herbicides approved for application over the tops of vegetable plants, do not use a sprayer that has been used with lawn herbicides.
Before using a herbicide in your garden, read the product label for a listing of vegetables it can be used on, the recommended rate of application, and the method of application. Never use a product that is not labeled, and do not exceed the recommended rate.
Dacthal—Several brand names are available. Dacthal can be used on a wide variety of vegetable plants. Applied correctly, Dacthal gives good control of most grasses and a few broadleaf weeds. This herbicide controls weeds as their seeds germinate. Therefore, before applying Dacthal, remove existing weed plants.
Trifluralin—Several brand names are available. Trifluralin is a preemergence herbicide used to control grass problems in the garden. Some planning of the garden to group trifluralin-labeled vegetables in one area is helpful when you use this herbicide. To obtain good weed control, mix trifluralin with garden soil. Cultivate soil to eliminate clods. Broadcast the recommended amount of either the granules or the liquid formulation. Granules are easier for most gardeners to use. After application, mix the herbicide in the top 2 inches of the soil. Two very shallow cultivations provide good mixing with the soil. Trifluralin is labeled for use before planting seeds of several vegetables and before setting transplants of others. Read the package label for a list of approved vegetables.
Poast is a postemergence herbicide that selectively controls grass weeds in several vegetables. Apply Poast to most grasses before plants reach 8 inches high. One application controls most annual grasses, but several applications may be required to control perennial grasses like bermudagrass. Mix a crop oil concentrate in the spray solution before application. Read the Poast label for specific instructions and approved vegetable crops.
Glyphosate—Formulations of this popular nonselective, postemergence herbicide are approved for limited use in the vegetable garden site. Most applications are for eliminating existing weed problems before vegetable seedling emergence and before vegetable plants are in the garden. Read the label for specific application instructions and limitations.