Herbicides in the phenoxy class of chemicals are widely used to destroy broadleaf weeds. They include herbicides such as Weed B Gone, Aqua Kleen, Salvo, Spectraclean, Green Sweep, Ultrastop and Weedone. According to a report by consumer health advocacy group Beyond Pesticides, this class of chemical is linked to cancer, reproductive toxicity, brain damage and toxicity to wildlife. Plants exhibit symptoms of injury from herbicide misuse.
Herbicides are divided into two categories; selective and non-selective. Selective herbicides are intended to destroy particular types of weeds, such as broadleaf or grasses. Non-selective weed killers destroy all plant tissue they come into contact with. Selective herbicides can become non-selective if they are misused, causing unwanted damage to cultivated plants near weeds.
Leaf chlorosis, or yellowing, is a common symptom of herbicide damage. The chemicals in many herbicides disrupt the plant process of storing energy (light) from the sun, causing plants to yellow, wither and die. Herbicide-induced chlorosis causes bright yellow leaf coloring. Foliar spotting may result from herbicide spray drift, causing burn spots. Both leaf chlorosis and foliar spotting can result in overall tissue death of the plant.
Twisted, cupped or otherwise distorted stems and foliage is a damage symptom of phenoxy herbicides. Damaging chemicals of this type are absorbed through plant roots and shoots. Dandelions and other nearby plants exhibit distorted growth patterns soon after the broadleaf weed killer is applied to a turf area. Woody plants such as grape and azalea are sensitive to phenoxy herbicide damage.
Whole Plant Symptoms
Some trees show a spiral pattern of damage of abnormal or dead growth from base to the top when there is herbicide damage. Toxic chemicals are absorbed through the root system, causing pervasive trunk and foliage injury. Herbicide spray drift often causes damage symptoms on half a plant or tree. Herbicide chemical damage can also mimic pathogen, vascular or insect damage. Professional diagnosis by a horticulturist is recommended.
Oklahoma State University Extension website recommends reading labels carefully and to "choose correct herbicides that least affect the plants and surrounding environment." Non-chemical weed control techniques include hand-pulling weeds, using thick mulch and planting cover crops. A 3- to 4-inch-thick mulch of straw, dry leaves, aged compost or newspaper prevents sunlight from reaching weed seeds, which prevents germination. Cover crops such as rye and vetch prevent weed growth and provide nutrients to soil.