Winter weed control starts now
BY THERESA FRIDAY Extension Agent Santa Rosa County

Weeds in the lawn are an issue for nearly every homeowner. Eliminating weeds requires an integrated approach and a good understanding of weed biology.

Many of our most common weeds are annuals. They complete their life cycle in one growing season. Those that complete their life cycle from spring to fall are referred to as summer annuals. Those that complete their life cycle between fall and spring are winter annuals.

Summer annuals, like crabgrass and chamberbitter, have just about completed their life cycle. They have reached maturity and have already produced many, many seeds. This late in the year, it's very difficult to control these weeds with herbicides.

Many lawn weed problems, however, are caused by winter weeds. These are cool season plants that germinate during early fall. They remain obscure, or at least innocent looking, during cold weather and then burst forth with a rapid flush of growth in early spring.

Questions about controlling winter weeds start coming in during March each year. Unfortunately, by then they have matured and are producing seed. In that stage weed killers are much less effective.

Now is the time to take action if your lawn has a history of infestation by chickweed, henbit, burweed, annual bluegrass or other cool season annual weeds.

Preemergence herbicides are applied prior to weed seed germination. If the chemical is applied after weed emergence, these herbicides will have little or no effect.

A general rule of thumb for application of a preemergence herbicide to control winter weeds is early October in north Florida. More specifically, it's when nighttime temperatures drop to 55 to 60 degrees F for several consecutive days.

Look for products that contain dithiopyr, pendimethalin or prodiamine. Because not all herbicides are safe on all types of grasses, be sure to read the label before purchasing. Ensure that the herbicide you buy is safe to apply to your type of grass. And as always, be sure to follow the label directions exactly.

Preemergence herbicides are generally effective in controlling weeds from 6 to 12 weeks following application.

Most herbicides begin to degrade soon after application when exposed to the environment. Therefore, to obtain season-long control, an additional application should follow approximately 6 to 9 weeks after the initial one.

Adequate soil moisture before and after application is necessary to activate most preemergence herbicides.

Preemergence herbicides do not prevent weed seeds from germinating. Instead, as the seed germinates, it contacts the herbicide barrier or zone that has been created in the upper few inches of the soil.

The seedling is killed because it came in contact with the herbicide. Therefore, to maximize your control, do not create gaps in the herbicide barrier by digging in the soil while the herbicide is chemically active.