What is this grass?

Asked November 3, 2013, 5:58 PM EST

This year my yard and the woods in Sligo Creek Park and Wheaton Regional Park experienced an unprecedented growth of the plant in the attached image. 1) Can you identify the plant? 2) Can you provide any information on eliminating it from the my lawn or preventing it from growing again next spring? 3) Can you provide any information on why it is so prevalent this year as compared to previous years? Thank you.

Montgomery County Maryland

1 Response

This is stiltgrass, also known as Japanese stiltgrass. It is a non-native plant designated invasive in Maryland (and everywhere else in the U.S.) Unfortuantely, unlike other grass which wants a lot of sun to grass, stiltgrass flourishes in shade, and thus has become the scourge of our forests and parks. Like most non-native invasive plants, it outcompetes our native plants, smothering and eliminating them so that it completely takes over.

Everything you can do to eliminate stiltgrass will help. It is an annual grass which must start again from seed each spring. If you can prevent it from producing seeds, you can get some control. It has very little root and it very easy to pull out of garden beds or even the lawn in small areas. You can mow it, but it will still produce some seeds on the cut stems so that is only a partial control.

In a lawn, the easiest approach (when it has become widespread) is to put down a crabgrass pre-emergence herbicide in early spring. It will prevent the germination of stiltgrass seeds as well as crabgrass seeds. However, it will not last the entire growing season, and for total control you will need to apply again in summer. The product bag will tell you how long it is effective. At that time, apply again.

Stiltgrass was particularly rampant this year because it likes moist conditions and we had a very moist spring and early summer. It also seemed to continue popping up later in the summer than usual, but we can't say why that happened for sure.

Keep in mind that weed seeds stay alive for many years in the soil, so if you do not address the problem, more and more seeds will build up in the soil, creating what is known as a "seed bank." That's why it is important to be persistent in combating stiltgrass each year.