As the weather turns warmer, many homeowners begin to take an interest in the care of their home lawns. Warm-season turf like bermuda, centipede and zoysia will start to come out of dormancy and begin greening up later this month. The cool-season fescue is actively growing. Here at Gwinnett County Extension, a high percentage of the calls we receive are on lawn care. One of the most frequent questions is about controlling crab grass, a dreaded weed in the home lawn.
From late spring to the first frost, crabgrass can invade large portions of the lawn, creating an unsightly appearance. Three different species of crabgrass invade our lawns and have similar growth and appearance, with some minor differences in their leaves. Crabgrass is troublesome because it is an annual weed, and a single crabgrass plant can produce 150,000 seeds in one season. Also, by being such a prolific summer annual weed, it outcompetes the desirable turf grass species. It then dies out in the cold weather, leaving large, dead voids in the turf. Despite being an undesirable weed, it is sometimes used as a forage crop for horses and other farm animals.
As the daily temperatures become warmer, crabgrass seeds will begin germinating. The best way to prevent crabgrass and other warm-season weeds is with pre-emergent herbicides. Several effective brands of crabgrass killers are on the market and can be purchased at any garden center. Most are granular and can be put out with a drop spreader. If applied according to label directions, they provide good control of crabgrass. The best time of the year to make the application is in early March when the temperatures are above 60 degrees for several days in a row. When the forsythia shrubs are in bloom is generally a good time to make the application.
Since we are under a total outdoor watering ban, apply before rain is forecasted, which will activate the herbicide. Do not aerate or dethatch the lawn after applying it. These herbicides are recommended only for lawns that are well established. Do not apply to lawns that have been recently seeded or have newly laid sod.
One of the most frequent questions I get is about the effectiveness of "weed and feed" fertilizers. In general, these products should not be used, since one of the active ingredients will be applied at the wrong time. Warm-season turf should be fertilized only during or after it has greened up. The pre-emergent herbicide should be applied before it has started to green up.
After the crabgrass has emerged, control is very difficult. Some post-emergent herbicides (ones that kill weeds after they have emerged) are effective in controlling the weeds only when they are small, when they are difficult to detect. So application of a pre-emergent herbicide is generally the best way to go in dealing with this weed. Remember, you need to follow the label directions in using any product on your lawn.
Healthy lawns with dense stands of grass are more resistant to crabgrass infestation. Crabgrass likes to grow in bare areas and on turf that is stressed.
Proper fertilization, mowing and watering will promote more vigorous growth and development of the turfgrass, thus reducing the ability of crabgrass and other weeds to become a problem. If the watering ban is lifted, water the lawn more deeply and less often.
Thorough soakings a couple of times a week will promote healthy deep root growth. Crabgrass weeds have shallow roots, and frequent applications of less water will encourage the spread of the weed while being a detriment to the grass. Mow the turf as high as possible, allowing the grass to shade out any emerging crabgrass and other weed seedlings.
Although crabgrass is an aggressive weed and can be difficult to control, proper use of pre-emergent herbicides and care to maintain a healthy lawn will reduce its ability to spread.
Timothy Daly is an agriculture and natural resources agent with the Gwinnett County Extension Service. He can be reached at 678-377-4010 or Timothy.firstname.lastname@example.org.