Fall weed control for your north Florida lawn

By Larry Williams, UF/IFAS Extension Agent, Okaloosa County

The cycle of life is ending and beginning for many lawn weeds during the fall here in North Florida.

Warm season or summer annual weeds like crabgrass, spurge and knotweed have completed about eighty five to ninety percent of their lifetime as we begin the month of October. By now they’re the dominant weeds in many yards. They have already done almost all the damage they’re going to do. They have reached maturity and produced hundreds if not thousands of seeds. They’re just waiting for the first heavy frost of late fall or early winter to go to weed heaven or somewhere else. Most people wait too late to ask about controlling these weeds.

Basically, this late in the year, it’s too late to bother with herbicides to control these summer annual weeds.  

The best time to control weeds is while they’re young and tender and before they have had the opportunity to reproduce. This includes cool season or winter annual weeds that are about to germinate.

Even though you may have missed the best time to control the summer annual weeds for this year, you’re right on time for controlling winter annual weeds.

Timing of the herbicide application is of utmost importance in controlling winter weeds that are about to sprout in home lawns all over north Florida. Common winter weeds that germinate in the fall and early winter include annual bluegrass, chickweed, henbit, hop clover, lawn burweed and Carolina geranium.

These and other winter annual weeds germinate from seeds during fall as the soil temperature cools and the day length shortens. The little seedlings usually go unnoticed at this time but continue to slowly grow through the colder winter months. Approaching spring, as the day length becomes longer and the soil temperature warms, all of these previously inconspicuous weeds put on a growth spurt.

Control measures should be attempted before the weeds go to seed.

If you intend to use a preemergence herbicide, apply it during October when nighttime temperatures drop to 55° to 60°F for several consecutive days. This will be just before the weeds emerge. Proper timing is very important. 

For season-long weed control and based on what the product’s label reads, a second application may be required about nine weeks after the initial application. To activate some products, irrigation or rain may be necessary following application. Because many preemergence products may interfere with lawngrass seed germination, delay reseeding six to sixteen weeks after application. This applies to overseeding a lawn with ryegrass seed, also.

Make sure to follow all label directions and precautions when using any weed killer.

Originally published Sept., 2007