Dr. Gouin's Bay Gardener

Battling Invasive Grasses

Q Help! crab grass is aggressively attacking the perennial bed alongside my townhouse. I’ve been fighting this fight on a daily basis, but this stubborn intruder is winning. I’m about to surrender. Any suggestions?

—Mary Bollman, Chesapeake Beach
 
A:Are you certain it is crab grass and not wire grass? Wire grass or Bermuda grass is much more aggresive than crab grass. Next to kudzu and bamboo, Bermuda grass, a perennial, is one of the most difficult weeds to control because it spreads by rhizomes as well as by seeds.
           
The rhizomes can travel underground at the rate of 12 to 18 inches per week in light soils in warm weather. It also produces an abundance of seed. The only non-chemical method of control is to cover the ground with asphalt paper for a couple of years so that nothing grows. It takes that long to kill the rhizomes as well as the crowns and about 40 percent of the seeds.
           
Bermuda grass can only be controlled with Roundup, a brand of glyphosate. I have done research with it since 1976, finding it one of the safest chemicals I have ever tested. It is approved for use by organic farmers in controlling weeds under the federal organic farming law that regulates what can and cannot be used for the production of food crops sold as organically grown. It has a long history of being safe to use. When used with a wick applicator, it is environmentally friendly.
           
Sorry, but this is one case that chemical control is the only effective means.
           
Crab grass is a summer annual. When decapitated it is easily killed.

Professor Emeritus Francis Gouin retired from the University of Maryland, where he was the state’s extension specialist in ornamental horticulture. Follow his column of practical gardening and plant advice every week, only in Bay Weekly. Ask Dr. Gouin your questions at [email protected].