Both Ailanthus and Microstegium vimineum (Japanese stiltgrass) have concentrated allelopathic chemicals in their roots, shoots, and in the former, lesser amounts in the leaves.

When interested/concerned about allelopathic effects of specific plants, you need to do a bit of research on the plants on an individual basis. Allelopathy is little understood, but we do know that every genus of plant has unique allelopathic properties (chemicals, mode of action, targets) and need to be evaluated on an individual basis.

I couldn't find any research supporting that seeds are an issue with these plants, why are you concerned about it? As long as the living roots remain in the ground, they will be the primary delivery system for allelopathic chemicals.

Nice explanation, rhizo. And I would second the suggestion to do research, as often the allelopathic characteristic is very plant-specific or limited, with a few plants or plant types being very broadly and strongly allelopathic while most others have minimal impact.

"How does alleopathy work exactly?" I have no clue and doubt that anyone on this forum can answer that question. I can however tell you about roadside eradication of TOH along the Baltimore beltway. Incredible thickets of thousands of stems were given the basal treatment and the trees died. They were left intact, they were too numerous to remove them plus the terrain was difficult. The dead stems are there still and other, desirable plants have filled in nicely. Regarding stiltgrass, this truly a nightmare alien. NOTHING eats it, it smothers everything in its path. It grows in sun, shade, wet, & dry even serpentine soils. On small residential properties hand weeding is possible, after all, this annual has virtually no root system and comes up easily. I don't see how mowing will control it, it can invade lawns and happily live beneath height of mower and set seed. If that wasn't bad enough another invader is on the way. Has Wavyleaf Basket grass come to NY state yet? HERE is a factsheet about it. Nothing eats these alien weeds and they have no diseases. They are the Norway rats of the plant world.

Sam_Md

I assume you heard about the issue in PA with the lantern fly and the ailanthus trees? If not, see below links.

https://www.agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Entomology/spotted_lanternfly/program-information/Pages/default.aspx

https://www.nytimes.com/2018/05/21/science/lanternflies-pennsylvania-crops.html

Thank you all for the information and articles (so interesting Lynn!) Provoked an ah ha moment to learn the plants that thrive with stilt grass are also Japanese, like honeysuckle. I'll include a Japanese husband who finds it nostalgic. Still wondering how long parts of a plant remain toxic after plant has been cut (roots left in ground) or composted (piles of stilt grass).