Prevent Crabgrass Now

— Written By and last updated by Sarah Roberson

Crabgrass is a summer annual grass that germinates in the spring in eastern North Carolina. It competes with lawn grasses and grows faster giving the lawn a bad look before the lawn grass needs mowing. Germination of crabgrass occurs when the soil temperature is 55 degrees for 3 days in a row. Around here it usually happens in March. Crabgrass germination continues over a 10 to 12 week period.

Crabgrass is best controlled using pre-emergence weed management products. These products form a layer of protection on or near the surface of the soil. Since germination starts in March, February is the time to get these products out. It is much easier to deal with crabgrass before you see it than after. Effectiveness depends on rainfall amount, timing, number of sunny days, and a number of other factors. It is important to follow label instructions carefully when applying these products.

Pre-emergence crabgrass control products must be activated by rainfall or irrigation to work. Usually 0.5 inch of rainfall or irrigation is needed to uniformly distribute the chemical compound in the upper portion of the soil.  Even distribution is important to create a chemical barrier across the surface. Pre-emergence weed management products work in one of three ways. The seed may absorb water containing the product, which may affect it enough to prevent it from germinating. Crabgrass may also be controlled as the first root emerges from the seed and absorbs water containing the pre-emergence product. The last scenario is that the underground portion of the emerging shoot absorbs the product. In all cases, death of the crabgrass seedling generally occurs before the shoot emerges above the soil line.

Calibration is one of the most important steps in applying any product to a lawn. This includes weed control products, insecticides, fungicides, and fertilizer. Calibration ensures that proper amounts are applied over a known area. Proper application of pesticides and fertilizers, which protects water quality, is possible only with a sprayer or spreader that is accurately calibrated. Pesticides applied with equipment that has not been calibrated may be misapplied by more than 10 percent. That may lead to need for repeat applications, damaged plants, excess cost, and contamination of the environment. Calibration instructions may be found on the instructions of some products or you can contact your local office of North Carolina Cooperative Extension.

The most common reason for failure of pre-emergence crabgrass control products is improper timing. Based on the way they work, it is important that these products are present when the seed or non-emerged seedling can come into contact with them. For crabgrass control, applications made before March 1 work best.

It is only necessary to make these applications if crabgrass has been a problem in the past. The best management practice for controlling crabgrass is a thick healthy lawn. Crabgrass generally germinates easiest in areas that have bare soil. These areas warm up quicker and have more soil surface light contact than thick lawn areas.    Crabgrass doesn’t have to compete with grass roots for water and nutrients in those areas.  I guess the next logical question is “What are some of the products that can be used?” There are a number that can be purchased and applied by homeowners. Look for products containing active ingredients like: benefin, benefin and trifluralin, bensulide, dithiopyr, indaziflam, metolachlor, oryzalin, pendimethalin, or prodiamine. Many of the products labeled for this have crabgrass somewhere in the brand name or trade name. They are often sold as Crabgrass Preventer. Most prevent other weeds also. Granular products are the most commonly available for homeowners. The two most common active ingredients available for homeowners are either pendimethalin or dithiopyr. They are not always found with the other chemicals but may be located near fertilizers or registers. Do not apply any product containing fertilizer to warm season grasses now. This is a waist of time and money, may injure the lawn by encouraging diseases, and potentially harms the environment since warm season grasses are unable to take up these nutrients now. Check local garden centers, hardware stores, fertilizer dealers, and home suppliers for availability. Read label instructions carefully to make sure products are safe for use on your type of grass. Always apply at labeled rates, calibrate application equipment, and wear personal protective equipment recommended on the label.

If you have gardening questions call 902-1705 anytime to leave a message. The Pitt County Extension Master Gardener Volunteers staff an office at the Extension office from 10 am to noon Monday and Thursday through February. You can also email them at pittcomgv@hotmail.com. You can always find more gardening information for our area at http://pitt.ces.ncsu.edu including links to our blogspot, facebook, and Twitter pages.

Written By

Photo of Danny LauderdaleDanny LauderdaleArea Specialized Agent, Nursery and Greenhouse, Eastern Region Serves 44 CountiesBased out of Wilson County(252) 237-0111 danny_lauderdale@ncsu.eduWilson County, North Carolina
Posted on Feb 24, 2014
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