Pre emergent for Japanese Stilt Grass - Ask Extension
I’m confused by the many pre emergents on the market that claim to help keep Japanese stilt grass seeds from germinating. I bought a property in 20...
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Pre emergent for Japanese Stilt Grass #924682
Asked February 17, 2026, 8:35 AM EST
I’m confused by the many pre emergents on the market that claim to help keep Japanese stilt grass seeds from germinating. I bought a property in 20855 last spring that was not mowed timely and the stilt grass grew tall and went to seed. Since owning the property, I’m mowing weekly and would like to further suppress the stilt grass as it has taken over my lawn. What is the favored pre emergent and timing to apply? Thank you.
Montgomery County Maryland
Expert Response
Any herbicide labeled for use on a residential lawn that includes Stiltgrass in its list of weeds controlled should, in theory, work sufficiently well, either as a pre-emergent or a post-emergent. The timing of application would depend on the exact formulation being used, so we defer to product label directions.
However, Montgomery County has a law regarding what pesticides can be applied to lawns, and in most cases, synthetic (non-organic) herbicides are prohibited. What products are allowed are not going to be selective, which means that a pre- or post-emergent used for Stiltgrass would potentially damage any desirable plants (like germinating turfgrass seed or lawn "weeds" you don't mind having for pollinator or nutrient-boosting value, like wild violets or clover).
Stiltgrass often recolonizes areas via seeds clinging to the fur of animal legs, typically deer. If feasible, keeping deer out of the property can help reduce the amount of new seed introduced each year back into the yard, even if you successfully manage to suppress any populations already present. Since Stiltgrass is an annual, at least all plants present one year will be dead the next, so it's only a seedling generation that needs to stifled. Unfortunately, while mowing does help to manage Stiltgrass growth and minimize its ability to flower and set seed, it still can produce seed heads on stems short enough to be missed by a mower. Stiltgrass can grow in a fair amount of direct sun, but favors semi-shade, which is also a condition that can make turfgrass struggle and not compete as well with weeds. If you overseed the lawn each autumn (we're assuming the lawn is tall fescue, not zoysia), that will help to keep the turf dense and better able to resist weed colonization/takeover.
If you are in the exempt area of the county (Laytonsville; it appears not), then information about candidate herbicide ingredients and timing recommendations can be found on our Japanese Stiltgrass in Home Landscapes web page. Generally, two applications of pre-emergent are used, one in early spring once the soil temperatures reach a certain level and trigger germination to begin, and a second as a follow-up several weeks later to catch any late-sprouting seeds.
Miri
However, Montgomery County has a law regarding what pesticides can be applied to lawns, and in most cases, synthetic (non-organic) herbicides are prohibited. What products are allowed are not going to be selective, which means that a pre- or post-emergent used for Stiltgrass would potentially damage any desirable plants (like germinating turfgrass seed or lawn "weeds" you don't mind having for pollinator or nutrient-boosting value, like wild violets or clover).
Stiltgrass often recolonizes areas via seeds clinging to the fur of animal legs, typically deer. If feasible, keeping deer out of the property can help reduce the amount of new seed introduced each year back into the yard, even if you successfully manage to suppress any populations already present. Since Stiltgrass is an annual, at least all plants present one year will be dead the next, so it's only a seedling generation that needs to stifled. Unfortunately, while mowing does help to manage Stiltgrass growth and minimize its ability to flower and set seed, it still can produce seed heads on stems short enough to be missed by a mower. Stiltgrass can grow in a fair amount of direct sun, but favors semi-shade, which is also a condition that can make turfgrass struggle and not compete as well with weeds. If you overseed the lawn each autumn (we're assuming the lawn is tall fescue, not zoysia), that will help to keep the turf dense and better able to resist weed colonization/takeover.
If you are in the exempt area of the county (Laytonsville; it appears not), then information about candidate herbicide ingredients and timing recommendations can be found on our Japanese Stiltgrass in Home Landscapes web page. Generally, two applications of pre-emergent are used, one in early spring once the soil temperatures reach a certain level and trigger germination to begin, and a second as a follow-up several weeks later to catch any late-sprouting seeds.
Miri
