If you are interested in controlling annual bluegrass, rescuegrass, henbit and chickweed (winter annual weeds) in your lawn, apply pre-emergent herbicide in early September.
If you are interested in controlling sandbur, goosegrass and crabgrass (summer annual weeds), apply pre-emergent herbicide in early February.
If you would like information on pre-emergent herbicides, contact the county Extension office.
Apply these products like a fertilizer according to the directions using a rotary spreader. Uniform coverage (apply in two perpendicular directions) is very important to prevent weed escapes. Some of these products will stain concrete, so make sure you blow it off your driveway when you are finished. It may also stain your pant leg and spreader. The product needs to be watered in with a 1/2-inch of water (run the irrigation until several tuna cans laid out randomly in the lawn are half-full).
The product will control winter annual weeds when applied in September and summer annual weeds like field sandbur when applied in February before the weed seeds germinate. It will not control perennial weeds like dandelion that come back from vegetative structures. The costs for these products will be around $26 per 12,000 feet.
Be careful putting herbicides on St. Augustine grass. The fewer herbicides placed on St. Augustine, the better. Even if St. Augustine is on the label, it may still be stunted for a month or more. Fall pre-emergent herbicide applications for winter annual weed control (henbit, chickweed, annual bluegrass) are safer on St. Augustine than spring applications, but they control different weed spectrums. One can use the rest of the bag the next season. The active ingredient can stunt root growth.
Do not apply the product anywhere you plan to plant seeds like vegetables or flowers or have wildflowers. You may need to apply again in July, but hopefully, a dense, aggressive turf will prevent sunlight from reaching the soil and stimulating summer annual weed seeds to germinate and a second application will not be necessary.
It’s too early for nitrogen fertilizers, so don’t apply a pre-emergent herbicide on a nitrogen fertilizer carrier. A good winterizer is high in potassium and iron with little nitrogen (5-0-31). Apply the nitrogen once a month starting in April. May would be better if you can be patient. You may just be fertilizing winter annual weeds. The more nitrogen fertilizer one adds, the more often one should mow. If one cannot mow more often than once a week, then use nitrogen fertilizer more sparingly. Always maximize the amount of slow release nitrogen and iron in the fertilizers for lawns. More is not better.
The most effective change in management most homeowners can make is to raise the height of their mower to the highest setting and mow regularly (only cut 1/3 of the blade off). Turf mowed regularly at a high setting will have longer roots and a closed canopy which will shade the soil, save water and not stimulate weed seeds to germinate.
For information, call the Wise County Extension office at 940-627-3341.
Todd Vineyard is a Wise County Extension agent.