I have been trying to get rid of this weed for several years. I can kill one year's growth,but it comes back the next year in a wider area. What and when should I use to get rid of it . Thank you for your assistance. California, MD
This is Japanese stiltgrass, a non-native, invasive grass that threatens native plants and natural habitats. It is now a major problem throughout Maryland and it is difficult to control.
Here is information about managing Japanese stiltgrass in a lawn. https://extension.umd.edu/hgic/topics/japanese-stiltgrass
Because of its seed bank (seeds can persist in the soil ~5 years) and its widespread presence, it will be a constant battle (and likely futile) to try to eradicate it entirely. During the growing season, keep the area mowed to help prevent the stiltgrass from forming seeds. This is tricky, however, because even stiltgrass that is mowed short can form seedheads. You can also handpull if possible and apply a preemergent in the spring. Keep up with lawn care best practices to achieve a healthy, dense turf (soil test, fertilize in the fall, mow high, etc.). https://extension.umd.edu/hgic/topics/best-practices-lawn-care
If you have Japanese stiltgrass in a surrounding area near the lawn (such as a woodland edge), you will have to hand pull (tackle small areas at a time) or use a recommended nonselective, post-emergent herbicide. Desirable plants will have to be protected from herbicide spray.
In sum, there are no easy solutions to this plant that has become highly invasive and widespread. In some case, people are just accepting it in their lawn because it is just too much/too difficult to control effectively. If you have deer in the area, they are effective dispersers of the seeds (carried on their fur).
Here is additional information from Rutgers University. https://njaes.rutgers.edu/fs1237/