Japanese Stiltz Grass
We live in St. John's area and are overrun with these grasses. They have come up into the established lawn and also out back where we have mulched open areas with ferns. Please help us before we are totally taken over with this invasive grass.
Japanese stiltgrass is a foreign invasive plant that is wrecking ecological havoc all over the Eastern U.S. Research is ongoing. We have been swamped with questions about stiltgrass this year, probably because weather conditions were optimal for it and it is increasing exponentially all the time.
Pull it out of your beds before it goes to seed in late summer/early fall. (Keep an eye on the tips of the blades, where you will see the seedheads emerge.) If you can't pull it all, spray or cut down the plants before the seeds mature. Try using a preemergent labeled for ornamental beds like Preen next season. Look on the label to see if you can use it around ferns. Apply it in March before it germinates.
In the lawn, use a crabgrass pre-emergent herbicide in early spring (early to mid-March). Since it germinates before crabgrass the pre-emergent should be applied a couple of weeks before you would apply it to control crabgrass. Here is our webpage (be sure to read the links, too) http://extension.umd.edu/hgic/problems/japanese-stiltgrass
Seeds stay viable in the soil for years, so one big key is to keep seeds out of the soil If you have a mower that can bag clippings, use it when the stiltgrass is going to seed. The rest of the year, we don't recommend bagging clippings. Also, be sure that the mower does not shoot clippings into beds or natural areas.
Thank you. I really hope this helps. We will only know for sure next year.