When to Apply Pre-Emergent to Bermuda Grass in Upstate South Carolina?

Bermuda Grass and Weeds

• Bermuda grass (Cynodon dactylon) grows best in climates with hot summers and mild winters, preferring USDA zones 7 through 10. Upstate South Carolina falls in USDA zone 7. Bermuda grass thrives in a variety of soil conditions, forming a thick lawn that holds up well to foot traffic and drought. The dense growth helps this grass choke out weeds, but does not eliminate all weed problems. For weeds that are already established, post-emergent herbicides or hand-pulling are the two main options. To prevent future growth of weeds, especially annual weeds, pre-emergent herbicides can be effective.

About Pre-Emergent Herbicides

• Pre-emergent herbicides prevent weed seeds from germinating. For this reason, they are particularly effective against annual weeds, such as crabgrass and common chickweed, which reseed themselves each year. Because they prevent seeds from sprouting, pre-emergent herbicides should not be applied when seeding a new lawn.

  To control crabgrass, prostrate knotweed (Polygonum aviculare), hardy in USDA zones 5 through 10 and other annual weeds that grow during South Carolina's summers, pre-emergents should be applied in the spring, before the seeds germinate. For winter weeds such as annual bluegrass (Poa annua) and chickweed, pre-emergents will need to be applied in the fall.

Applying Pre-Emergents in the Spring

• For upstate South Carolina, you can begin applying pre-emergent herbicides in mid-March before weed seeds germinate. With crabgrass, the seed germinates when the temperature in the soil reaches 52 degrees Fahrenheit. Test soil temperature with a soil thermometer, or make sure you apply the pre-emergent before the first frost-free date of the year. In upstate South Carolina, the last frost date is generally in April. The specific date will vary based on your location. For example, there is only a 10 percent chance of frost in Anderson by April 15.

  A typical pre-emergent herbicide containing the chemical Dimension can be applied in granular form at a rate of 1.9 to 4.3 pounds per 1,000 square feet. Herbicides containing the chemical pendimethalin can be applied at 2 pounds per 1,000 square feet. Read usage instructions on the label, as rates vary depending on the brand and type of herbicide.

Applying Pre-Emergents in the Fall

• Winter weeds thrive in cool conditions, and can take over a yard or garden during the colder months of the year. These seeds germinate in the fall, and will not be stopped by spring applications of pre-emergent herbicides. To control winter weeds, herbicides should be applied in late summer or early fall.

  For upstate South Carolina, the time to apply pre-emergent herbicides for winter weed control is mid-September, while the temperature is still above 50 F. If you are over-seeding the lawn for winter color, do not apply pre-emergents, as they will prevent the grass seeds from germinating.