When good lawn chemicals go bad
Herbicides are chemicals used to eliminate weeds from your lawn turf. Lawn herbicides are available in pre-emergent types that prevent weeds from sprouting, and post-emergent types, which kill them after they have sprouted.
Homeowners should research carefully before using weed killers. Some products can cause severe damage to grass and landscape plants when used improperly.
SIGNS OF INJURY
You may see signs of herbicide damage shortly after applying the product to your lawn areas. The grass may become yellowed, a condition called chlorosis, or it may appear striped with colorless areas.
Grass plants may brown and die. Wilting and curling of leaves can also occur. Herbicides should not be used on newly planted grass, which can brown and die in large patches.
THE RIGHT HERBICIDE
Weed killers come in a variety of types. Some of these are “selective” in that they only kill some types of weed plants. Others are “non-selective,” which means they will kill any type of growing plant, so they must be used with care.
Glysophate, marketed under the brand name Roundup, is one of these non-selective weed-killers used to kill weeds on driveways and sidewalks. It can kill your lawn grass if used incorrectly.
Homeowners should identify the type of turfgrass used in their lawns so they can choose the right herbicide product. St. Augustine, a grass used in warm climates, cannot tolerate many herbicide compounds.
Always read labels carefully to determine if the herbicide is safe for your type of grass. When in doubt, contact your local agricultural extension service for advice.
REPAIRING DAMAGE
If you see damage on your lawn soon after applying an herbicide, you may be able to save the grass by employing a few techniques.
First, water the lawn liberally to wash the herbicide off the grass plants. This method will not help herbicides that are soil active. It will merely wash the compound further into the soil. You can, however, dig a slight trench around damaged areas to cut the roots of the grass plants to prevent the weed killer from being taken up into plant cells.
If damage is severe, you may have to re-seed or re-sod areas of your lawn with the most injury. After repairing your lawn, do not use herbicides for at least six weeks after re-seeding or re-sodding to allow the new grass to develop a strong root system.
PREVENTING INJURY
The best way to avoid expensive grass and plant injury from herbicides is to prevent it from happening. Follow label directions whenever you apply weed-killing products. Use only the amount recommended by the manufacturer.
Don’t mix chemicals together. Avoid drift problems by refraining from applying herbicide when it is windy. Use only the amine or low-volatile forms of 2, 4-D herbicide. Do not use soil active herbicides where run-off can carry it to non-target areas.
Be careful when applying soil, manure or other amendments to your property. They may contain herbicides to kill weeds. Know the source of the materials. Herbicide injury often occurs when you apply herbicides in hot weather. Only apply herbicide when the temperature is below 80 degrees Fahrenheit, or as directed on the bottle.
WEED AND FEED
Weed-and-feed combination products that combine an herbicide with fertilizer can be damaging to turf grass and landscape plants.
The main problem with these products is that fertilizer generally needs to be watered into the soil, but herbicides need to be left on the leaves in order to work properly.
Also, if you need to re-apply weed-killer, you will also be re-applying fertilizer, which is unnecessary and can find its way into local waterways. It’s generally best to weed and feed in separate operations.