EXTENSION CONNECTION: Timing is everything when controlling lawn weeds

Larry Williams | Special to the News Bulletin/USA TODAY NETWORK

CRESTVIEW — Hot summer months are not the time to be using most lawn herbicides.

One issue is the heat of summer. Most lawn herbicide labels include statements such as the following:

“Do not apply when temperature exceeds 90°F.” “Do not broadcast apply this product when air temperatures are above 90°F (85°F for St. Augustinegrass) unless temporary turf injury can be tolerated.”

Every year we’ll see lawns that are injured or killed because of lawn herbicides being applied when temperatures are too hot.

Mature, well established weeds like this crabgrass are much more difficult to control in summer than when they are small and not well established.

Summer is usually a rainy and windy time of the year. Many lawn herbicide labels include statements such as the following:

“Allow 12 hours after application before watering lawn for maximum effectives on listed weeds.” “Apply only when wind is no more than 10 mph.” “Applying this product in calm weather when rain is not predicted for the next 24 hours will help to ensure that wind or rain does not blow or wash pesticide off the treatment area.”

It is critical to read and follow the label directions and precautions for any pesticide you use. Pesticide labels, including herbicides, include the following statements.

“To the extent consistent with applicable law, the buyer assumes all risks of use, storage or handling of this product not in accordance with label directions.” “It is a violation of Federal law to use this product in a manner inconsistent with its labeling.”

Mature weeds

By the time summer arrives, many of the lawn weeds are mature, which means they are well established with extensive root systems.

These mature, well established weeds are much more difficult to control. They are more susceptible to herbicides when they are small, young and not well established. Also, these mature weeds have been allowed to produce countless numbers of seeds as they move into summer. Most weeds are prolific seed producers. For example, a single crabgrass plant (a common summer lawn weed) can produce 150,000 seeds.

Applying a preemergence lawn herbicide in February to help prevent summer annual weeds such as crabgrass or applying a postemergence lawn herbicide during spring while the weather is mild and before the weeds are out of control simply makes more sense than waiting until summer.

The best options now with lawn weed control involve continuing to follow good mowing practices, maybe hand removal of some weeds and just simply waiting it out until next February and spring to worry with the use of lawn herbicides.  

In the meantime, you may want to read the following UF/IFAS Extension publication on lawn weed control: https://edis.ifas.ufl.edu/pdf/EP/EP14100.pdf.

 Call 850-689-5850 to have a printed copy mailed to you.

Larry Williams

Larry Williams is an agent at the University of Florida's Institute of Food and Agricultural Sciences Extension office in Crestview.