Japanese Sttiltgrass

Asked September 28, 2020, 12:07 PM EDT

Is there an application for Japanese Stilt grass that is so out of control that it is beyond picking?

Baltimore County Maryland

1 Response

Is the Stiltgrass growing in a lawn or in flower beds? Some of the control measures may vary depending on the weed's location. Japanese Stiltgrass is an annual weed, and it will die-off completely this winter as soon as we experience regular freezes. The seeds in the soil, however, will remain viable for years, and are often carried into yards on animal feet (mainly deer). In that case, keeping deer out contributes a lot towards the success of long-term control. This late in the season, keeping the existing Stiltgrass from going to seed as best you can is the only approach needed. If in lawn, this would just mean mowing heavily-infested areas as low as you can (though avoid doing this to areas with mostly turfgrass, as it detriments its health), and in flower beds, the most practical (though tedious) approach is to simply pull plants up as using a string trimmer to cut their developing seeds off will probably also damage desirable plants in the bed.

Next year, a pre-emergent herbicide is the most practical approach to control. This weed germinates even earlier than the early-sprouting crabgrass, so measures must be in place around two weeks prior to crabgrass control timing. More information is available on this page: https://extension.umd.edu/hgic/topics/japanese-stiltgrass. Take note that a second application of the pre-emergent will be needed later in spring to catch any late-sprouting seeds; the product's label will give specific instructions. If using a pre-emergent in flower beds, make sure it lists any desirable plants you have growing in that bed as safe in their tolerance of the chemical. While pre-emergent chemicals are meant to only impact germinating seed, not established well-rooted plants, it's safest to check for known sensitive species on the herbicide label first. Not disturbing the soil after application is key, or the barrier of herbicide will be ruined and ineffective, so avoid installing any annuals or early-season plantings in treated beds; otherwise, if you do, you will simply have to hand-pull any Stiltgrass that appear there afterwards.