Herbicides, commonly known as weed killers, are natural or chemical products that destroy or inhibit the growth of unwanted plant life. Sprayed chemical herbicides easily drift onto nearby vegetable plants. Chemical residue may remain in the soil and leach into water supplies. It is illegal to use herbicides without following the label directions correctly. There are several preventative weed control techniques to use in the vegetable garden to replace the use of chemical herbicides.
Herbicides are classified according to their action on plants. Non-selective herbicides destroy or prevent plant life regardless of species. Selective herbicides are more toxic to some plants than to others. Broadleaf weeds and grassy plants are targeted by two different types of herbicide. Non-selective herbicides damage vegetables as well as the weeds that surround them.
The difference between non-selective and selective herbicides is not necessarily the formula, but the weed killer's concentration and when it is applied, according to University of Nevada Extension horticulturist Dr. Angela M. O'Callaghan. A selective-type herbicide may destroy nearby ornamental plants and vegetables because of wind drift. Vegetables may be affected by weed killer used on the lawn.
Younger vegetable plants are more susceptible to damage caused by contact herbicides. Herbaceous (non-woody) plants such as zucchini and tomato are more permeable to systemic and contact toxins because of their fibrous, fleshy stems and leaves. Systemic herbicides such as Roundup are translocated from the point of entry to other areas in the plant system.
Typical symptoms of herbicide damage to vegetables include stunted growth, red or purple veins, yellow leaf tissue, twisted leaves and dead leaves. Symptoms of herbicide injury may be similar to symptoms of other types of damage such as drought, excessive soil compaction and nutrient deficiencies. Consult the local county extension service for additional advice on distinguishing plant problems.
Preventative weed control techniques such as mulching minimize the need for herbicides in the vegetable garden. Straw, shredded bark, dry leaves, newspaper and compost are mulch materials that are used in a 3- to 4-inch layer around vegetable plants. Corn gluten is a pre-emergent herbicide that prevents some weed seeds from germinating. Cover crops such as vetch are used in sustainable agriculture farms to prevent weed growth.