Now is the Time to Think About Summer Weeds in Your Lawn
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It is hard to even think about dealing with summer problems in the landscape when it is the first of March and we’ve not even got to Spring time weather yet. There are probably not many people thinking about summer weeds, like crabgrass and goosegrass, which sometimes show up in their lawns. Believe it or not as the soil temperature warms, it will not be long before these annual summer weeds will begin germinating in the soil.
To best control annual summer weeds, such as crabgrass and goosegrass, it is recommended to apply a preemergent herbicide in early March around the time when the forsythia shrubs are blooming. When we talk about controlling weeds, you want to find the “weakest link” in order to get the best control. The “weakest link” for annual weeds, which come back in a lawn from seed every year, is to stop them when they are young and just germinating. When a preemergent herbicide is applied, you are creating a layer of herbicide in the soil just below the grass roots. This layer serves as a barrier, killing young weed seedlings just after they germinate before they emerge through the soil surface. In order for all of this to take place; the herbicide must be applied just before the weed seeds germinate so the barrier is in place when weeds try to emerge.
The reason we recommend applying a preemergent herbicide now to control summer weeds is because it won’t be long before they will be germinating in the soil. Crabgrass germinates when the 24-hour average soil temperature reaches 55°F, while it is 60°F for goosegrass. These soil temperatures typically occur in mid- to late- March.
Now the question of what to apply. There are several herbicides that are recommended for these summer weeds including: benefin, dithiopyr, oryzalin, pendimethalin, and prodiamine. These are the chemical names and often sold under various trade names. Some will be referred to as “crabgrass preventers.” To find the correct herbicide, look for these chemical names on the front label under “Active Ingredients.” It will often be in tiny print, so you have to look closely but it will be there. Use caution when selecting one of these herbicides because they sometimes will have a fertilizer include with them. Now is NOT the time to be applying fertilizer to warm-season lawns, like Bermuda and Centipede. Applying fertilizer now could actually harm lawns as they begin to come out of dormancy.
When applying one of these herbicides, uniform coverage during application on your lawn is critical so that a weed doesn’t find its way through a spot that did not get treated. Also, most of these preemergent herbicides must receive rainfall or irrigation after application which means you should watch the weather to time your application before rain is forecasted. As with any pesticide, it is important to read the label and follow directions on to how to correctly apply the product.
Unfortunately, this preemergent application is not a cure-all for summer weeds like crabgrass. While preemergent herbicides are effective, they will not provide good weed control if a lawn is not properly cared for. Encouraging a healthy lawn is the first step to preventing any weed. Encourage a dense, healthy lawn by mowing on a regular schedule to the correct mowing height and correctly applying fertilizer at the correct time and amount for your lawn type. The N.C. Cooperative Extension Service in Wayne County has lawn maintenance calendars with this type of information for your lawn type available at our office.
Even though we are still having some winter-like weather outside, don’t forget to go ahead and stop those annual summer weeds before they emerge. Taking care of them now could save you a lot of headaches this summer.
Recommendations for the use of agricultural chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this article does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical.
Jessica Strickland is an Agriculture Extension Agent, specializing in horticulture for North Carolina Cooperative Extension in Wayne County.