This growing season, in addition to being very wet and moldy, has also been a boon to an invasive grass widespread in Carbon County. The villain’s name is Japanese stiltgrass (Microstegium vimineum).

By now stiltgrass has gone to seed and is near the end of its annual cycle. However, since each plant can produce a thousand seeds and those seeds can remain viable for at least three years, it will be back.

I’ve got a meadow of it in my lower yard where I haven’t been able to mow much due to rain. Left alone, stiltgrass grows up to 3½ feet tall, and that would be my lawn. Stiltgrass grows over obstacles and smothers the competition. Once it gets long, the rotary mower has trouble cutting it because it flattens like a crop circle instead of being sucked up into the mower blade.

Stiltgrass is really easy to pull because it doesn’t seem to have much of a root system. However, pulling it creates soil disturbance, and that is exactly what the seeds need to germinate next year. Unfortunately, pulling up stiltgrass is very satisfying and addictive. If you do it (like I have), the only remedy is to cover the disturbed earth with 4 to 6 inches of mulch so you deny the seeds the sunlight they need to germinate next spring.

You can mow stiltgrass, but that won’t stop it from producing flowers and seeds. According to one study, the best outcome from mowing was to cut right down to ground level (0 inches). That was the nuclear option because it also killed the rest of the lawn.

Stiltgrass grows in sun and shade. It grows in lawns, in garden beds and in the woods. It roots at its leaf nodes and sends out runners. It changes the soil chemistry where it grows to make the land less hospitable to trees. So far, nothing eats it, even deer.

New York State and Cornell University published a fact sheet offering a control strategy to landowners. The first step is to mow the stiltgrass when it is in flower to prevent it going to seed. The second step is to use a pre-emergent weed killer to stop the seeds from sprouting next spring. Limit soil disturbance such as tilling and pulling weeds, and mulch areas where you do till and weed.

There is also evidence that annual rye grass can outcompete stiltgrass because its seeds germinate earlier and are vigorous growers. For that reason it is possible to use annual rye to rehabilitate areas in the lawn where you’ve removed stiltgrass.

If you get your patch of stiltgrass under control or even eradicated, you will still be bombarded with seeds from your neighbors and from the woods. That means you need to be vigilant. I’ve personally noticed that it can’t defeat our native ferns and it can’t germinate in dense turf. It also didn’t grow in an area I covered with 4 inches of wood chips to eradicate another invasive plant.

The link to the article from Cornell University is https://bit.ly/2OAYxl7. There is also an extensive article published by the USDA at https://bit.ly/2xYropN.