Winter Weed Control in Lawns
The mild temperatures that metro-Atlanta has been enjoying this winter have implications for weeds in your lawn next summer, and Crabapple LandscapExperts are prepared.
Measuring Soil Temperatures
Weed seeds such as crabgrass ripen each fall and are dropped in lawns where they lie dormant during the winter, and germinate when spring soil temperatures reach 50+ degrees F. Fifty weather stations across Georgia collect data for weed scientists at the Georgia College of Agriculture and Environmental Sciences every year by taking temperature readings in the soil at one-half inch depth. When the temperatures reach 52 degrees F. or higher those crabgrass seeds will begin to germinate and it is the time to apply weed killer specifically to slow down that growth.
In typical years, March 1 is usually the date for application of pre-emergent herbicide, but this year, theLandscapExpert team will be on call a few weeks earlier to apply any weed killer they deem necessary. Dr Gerrit Hoggenboom oversees the network of weather stations across the state and releases the data to landscape companies who care enough to know the best.
In metro-Atlanta we are careful to apply the pre-emergence weed killer while the lawn is dormant and BEFORE it is warm enough for the crabgrass seeds sprout. This group of herbicides controls weeds during the weed seed germination process, and refers to pre- (before) emergence- (sprouting). If green growing weeds are seen in the lawn, it is too late to apply a preemergence herbicide. When applied in the late winter months, preemergence herbicides provide season-long control of summer annual weeds such as crabgrass, goosegrass and sandbur.The timing may seem like a little thing to property managers and HOA reps, but pre-emergent herbicide will not kill crabgrass seedlings that have already sprouted (or emerged) from their seeds. Pre-emergent is another way to say “pre-sprouted,” before the seed “wakes up,” and the tiny root (known as the radical) begins to grow.
Crabapple recommends preemergence herbicides only for turfgrasses that have been established for at least one year, or preferably more, because severe injury can result if a preemergence herbicide is applied immediately after sprigging or sodding (zoysiagrass, bermudagrass, St. Augustinegrass, centipedegrass). Preemergence herbicides form the backbone of weed control programs. They do not control all weeds that may be present in a lawn, but they are effective for many of the most common lawn weeds that plague commercial properties during the summertime.
Advantages of Preemergence Herbicides
Some of the advantages of using preemergence herbicides include:
- Preemergence herbicides are applied prior to weed seed germination and emergence.
- Many preemergence herbicides are available in granular formulations. Granules are easier to apply than sprayable formulations. Additionally, granules are not susceptible to spray or vapor drift that can occur with sprayable formulations.
- Most ornamental shrubs, trees and flowers are tolerant of and several are labeled for preemergence herbicides, while postemergence herbicides often can cause injury to ornamentals.
- Preemergence herbicides do not cause injury to established turfgrasses. In contrast, most postemergence herbicides will slightly injure or yellow turfgrasses for a short period after treatment.
- Preemergence herbicides are usually applied to an entire lawn area.
The LandscapExperts are keeping an eye on this unusually mild winter so you won’t have to worry.