When it comes to controlling crabgrass in a lawn, an ounce of prevention is really worth a pound of cure. Using a pre-emergence herbicide soon will be much easier than trying to kill the mature weed in your lawn this summer.
You may see crabgrass in your lawn every year, but it is important to realize that it is an annual plant. Crabgrass sprouts from seed, grows to maturity, sets seed, and dies all during a single growing season. In other words, the crabgrass you see sprouts from seed each year. You can prevent the seed from sprouting in the spring, however, by using a pre-emergence herbicide.
That brings us to a simple fact. Crabgrass seed germinates or sprouts when soil temperatures at a 4-inch depth reach 53-58 degrees F. This usually occurs from mid-
February through sometime in March depending upon weather conditions. How do you know when soil temperatures are nearing the trigger point? Well, the old time rule of thumb was to get your pre-emergence herbicide spread before the Forsythia blooms in the spring.
If you are a more technical person, then visit UGA Weather Network web site at http://www.georgiaweather.net/ Click on the link to Covington and then “current conditions.” The current conditions at the weather station at the Newton County Agriculture Center will be displayed. As I write this, the 4-inch soil temperature is 40.3 degrees F. The problem that a lot of people have with preemergence weed killers is that they do not apply it at the right time. As the name implies, you put it out before the weed emerges from the seed. Once the seed sprouts, it is like closing the gate after the horse has already left the barn!
Remember that it is better to be a little too early with your application that too late. Recent research has indicated that pre-emergent herbicide applications in January still have given acceptable crabgrass control. The weed killer does not break down as rapidly in the cold weather as it does later when the temperatures begin to warm.
There is another important point to remember. Pre-emergent herbicides can’t distinguish between friend and foe. Don’t overseed your lawn soon after applying a crabgrass preventer. The weed killer could inhibit the sprouting of your fescue seed as well as crabgrass seed. Young fescue can also be sensitive to some weed killers. Be sure to check the label on the product you are using and observe the proper time intervals between herbicide application and overseeding your lawn.
If you want the best performance out of your spring pre-emergence treatments, then I suggest the following:
1. Apply the product at the recommended time and rate according to the label.
2. Apply the product before rain is expected or water it in with 1/2 inch of irrigation water if the label requires it.
3. Be sure to calibrate your application equipment.
4. Delay mowing until after a rainfall or irrigation.
5. Properly maintain your turfgrass throughout the whole year.
Pre-emergence herbicides are wonderful tools to use in maintaining a healthy beautiful lawn. We just have to remember to use them the right way at the right time. Contact your local extension office for specific pre-emergent herbicides that best fit your lawn needs.
Ashley Best is the Agriculture and Natural Resources Agent with Newton County Extension Service. She can be reached at abest22@uga.edu.
