As summer is peaking so is the time to focus on removing
Japanese stiltgrass, Microstegium vimineum.
At this time (beginning of August) in the Mid-Atlantic region this invasive grass is putting
on a growth spurt, but has not yet begun to develop viable flowers.
Season | Actions | Pros | Cons | Comments |
Late Winter Early Spring | Pre-emergent treatment | Effective in lawns and smoother (even) surfaces with access to soil surface. Allows lawns and perennials to get a head start. | Will affect all germinating seeds for several months. Uneven coverage on rough surfaces. Application needs to be at the right time. | Takes at least 2 years to knock down seed bank to see significant progress. More time to complete elimination, if ever. |
Late spring-Summer | Herbicide | Grass selective herbicide leaves broad leaf plants and some sedges intact. Try products containing Fluazifop-p-butyl | Difficult to control collateral damage, especially with non-selective herbicides | Targeted application and use of selective materials may limit side effects. |
Late spring-Summer | Pulling | Non-toxic and selective. Opens space for other species. | Labor intensive; left over stilt grass will expand to fill gaps. | If removal is not complete this will need to be repeated at the end of summer |
Late summer/Early fall | Cutting/ pulling/ burning | All methods to reduce the amount of seed | Need to complete actions before seed begins to ripen. | Copious amounts of seed being produced, need to be thorough and avoid spreading any ripened seed. |
While it is too late to count on herbicides cutting close to the ground level and pulling at very effective methods to employ at this time in order to prevent Japanese stiltgrass from reproducing. Because this is an annual grass, keeping it from reseeding goes a long way to eliminating from your environment. In wooded areas and existing beds where there are many desirable plants intermixed with the stiltgrass I opt for pulling as my preferred approach. Since it has grown fairly tall by this time, I usually pull it by the handfuls then leave it out in the sun to dry. If you are weed whacking it you could leave the cut grass in place to dry; however, I’ve read that doing this can generate a thick layer of thatch that can be difficult for other plants to grow through. Whenever possible I will rake out the cut grass and leave it in the sun. If I’m confident that there is no viable seed in the stiltgrass I will mow over the dried grass to help return that organic material to the soil.
I’ve noticed that this year that the stiltgrass is more brittle and harder to pull cleanly out of the ground. This may be due to the drier weather that I am experiencing at this time. I’m afraid that I may be leaving more rooted fragments that may be able to regenerate. I will try to time my next pulling campaign to be after a significant rainfall to soften the soil.
Another thing I’ve noticed this year is that the plants that I am pulling up have multiple rooting points along the stem. I’m thinking that as I am reducing the number of stiltgrass plants, year by year, there is more room for them to spread laterally. So a partial success, but it means that there is still more work to be done.
Looking over my property I see that the most significant reduction in Japanese stiltgrass is where I have applied a preemergent herbicide in early spring. This year I applied Dimension™ (dithiopyr) at the higher recommended rate. This is expected to be effective for 3-4 months. It was applied at the time recommended for crabgrass control (380 GDD(32°F)), or about the time when the forsythia were coming into full bloom. I am seeing next to no stiltgrass in many parts of the lawn as well as in the treated parts of my ‘mown meadows’. Better results are seen where I have treated for at least two consecutive years. In these meadows and in the more natural areas I try to avoid treating the same area with a preemergent two years in a row. This is to allow the seeds of the many desirable plants to germinate on the off-years.
As far as native plants that compete well against Japanese stiltgrass, golden ragwort, Packera aurea, seems to actually suppress the growth of stiltgrass. Virginia wild oats, Elymus virginicus, and bottlebrush grass, E. hystrix, compete well. What I believe to be fowl manna grass, Glyceria striata, has been able to out compete Japanese stiltgrass in shady moist areas. This grass develops early in the year with tall, thick growth that shades the ground. The downside of this grass is that it dies back to the ground after going to seed in late June.
This photo, taken at the end of May, shows thick growth of a grass that I believe to be fowl manna grass. The area inside the white circle has been free of stiltgrass for the past two years. |