I recently attended the Connecticut Invasive Plant Conference at Uconn. In the afternoon, there was a panel discussion about invasive plant control and a question was posed regarding the control of Japanese Stilt Grass in a large wildflower meadow. The person asking the question felt his garden was doomed due to the invasion of Japanese Stilt Grass. He said he had tried everything and he was losing the battle. He thought he would eventually lose his beloved garden. His question was how would the panelists control Japanese Stilt Grass in a large planted meadow. All 3 professionals were looking at it as a post emergent control issue. I mean, that was how the question was posed. “Stilt Grass is taking over my large garden, I’ve tried everything and I’m losing the battle”. The discussion went on for 10-15 minutes and the answers from the experts were driving me crazy. They were only focusing on post emergent control. There are many post emergent herbicides you could use to kill Japanese Stilt Grass but as the person with the problem communicated, it’s a large area with dense plantings. It was virtually impossible to apply a post emergent herbicide without killing a lot of desirable plants and without each application taking days to apply. Trying to spray the target yet avoid the desirable plants with a non selective herbicide would definitely be time consuming. The conversation even turned to chemicals that would knock down the grass and damage the perennials/shrubs but wouldn’t kill them. One of the panelist even suggested flame throwing using a propane torch to selectively damage the grass. What? That obviously came from someone who hasn’t used a propane torch to control weeds. If you’ve ever tried to flame a garden or driveway, it takes forever and it’s not that easy to pinpoint extreme heat to select areas. Torching is more like using a non selective herbicide. Expect to damage a lot of plants in a densely planted garden. Keep in mind that propane and all other organic approaches unfortunately only kill top growth. Those approaches don’t give you any systemic properties which could be important if you were dealing with a perennial weed. Japanese Stilt Grass is an annual so systemic properties in a herbicide isn’t that important.
Half the battle with eradicating invasive plants is to know how they grow, how they survive and what their life cycle is. Unlike Knotweed and Mugwort, I feel that Japanese Stilt Grass is a relatively easy plant to figure out and control. Well maybe not control as in eradicate but at least to manage. Let’s face it, invasives are here to stay. With invasives, it’s all about management even if the goal is total eradication.
Japanese Stilt Grass is an annual. It does not survive our winters and needs it’s own seed to germinate year after year. In the situation above, the person could pull the plant but this creates another problem and that’s soil disturbance. Disturbing the soil is not something you want to do in a meadow planting. Why? Because soil disturbance brings new weed seeds to the surface, perpetuating the problem or worse, a new problem. You could cut the plant, leaving the roots undisturbed. In a large area, that could possibly be done using a string trimmer but would be difficult in a densely planted garden. Here’s the key to management. Japanese Stilt Grass starts setting seed in August. Cutting the plant low in August and keeping it low through the first frost would be a good strategy to minimize future seed production but the area sounded too large and the planting too dense for this approach. The only way to address the problem in my eyes and something the presenters never touched on until I posed the questions was to broadcast a pre-emergent herbicide over the entire meadow. I know, it’s a non organic approach but it’s the approach I would recommend. Unfortunately, this approach wouldn’t allow any self seeding wildflower to set seed either but I feel like this is really the best approach in a situation like this.
After a couple of seasons, I would slowly dial back herbicide applications, section by section, to see how much Japanese Stilt Grass comes back. At that point, I’d overseed the area with a mix or annual and perennial seed in the spring. We know, competition and plant coverage often minimizes annual, invasive plant problems. If the weed comes back after stopping the pre-emergent, it will hopefully be a lot less than before so it could be managed by cutting. If the weed was still a major problem, I’d go back to pre-emergent applications for another couple years.
If you are really opposed to non organic approaches. The only thing you can do is cut the plant, starting in August and seed, seed and seed more desirable plants every spring and hope the extra seed naturally squeezes out the problem.
