The Best Time to Treat Lawn Weeds in South Texas

Texas has four hardiness zones, with the lowest average temperatures starting at 10 degrees below zero. Add 40 degrees to that number and you get close to the average lows along the Gulf Coast. If you were moving from the panhandle town of Texline, Texas, to the most southern town of South Point, Texas, you could extend the growing season almost 10 weeks, adding one week for every 100 miles you traveled. The vast difference in the Texas growing season makes it difficult to know exactly when to treat lawn weeds in South Texas.

USDA hardiness zones 9a and 9b lie in the area of Texas, south of San Antonio and Houston to the Gulf Coast. The typical growing season for this South Texas zone is from mid-February through mid-December, with a summer interruption of about eight to 10 weeks of extreme heat. The zone's average lowest temperature reaches between 20 and 30 degrees Fahrenheit. The times to treat your lawn for invading weeds in the southern area of the state are going to be earlier and later than the rest of the state.

These weeds are treated during the late spring and early summer with MSMA, when the daytime temperatures average 90 degrees. For South Texas, the time period for these temperatures range from late April to late May. Grassy weeds include dallis grass, Johnson grass, crabgrass, grass burs, and winter grasses. You cannot use MSMA on St. Augustine or centipede lawn grasses.

Broadleaf weeds include dandelions, poison ivy, clover, henbit, ground ivy, chick weed, and dichondra. Apply most broadleaf weed killers with active ingredients such as, Isoxaben and Dimethoxybenzamide to a well established South Texas lawn when the average daytime temperatures reach 70 degrees Fahrenheit. For South Texas, these temperatures occur from late January to mid-February. There are other broadleaf weed killers that you can use during the summer and fall months, check the product's label before applying.

Use pre-emergence herbicides on the seeds of annual weeds. Annual weeds, such as crabgrass and grass burs die out each year, but before they do, they spread thousands of seeds that need killing before they germinate. Spread pre-emergence herbicides in the early spring, between mid-January to mid-February to catch the seeds before they start growing. Apply pre-emergence to your South Texas lawn once more during the late summer, from late October through mid-November, to kill the seeds that these weeds produced during the growing season.