Sounds like something that might compete with a biennual like GM,but probably would be ineffective in controlling a deeply rooted perennial like jap knotweed.A single knotweed plant can cover several acres,existing as one huge clonal group,with most of its biomass existing underground as an extensive root system,Simply seeding on top of it would have little effect.Preventing that root system access to photosynthetic energy for an entire year has been my control stratagy,By placing black plastic tarps over the entire infected area for no less than 12 months and herbaciding anything that peek out from the edges Ive achieved 100% kill rate.Collecting the GM plants while they're fully loaded with their seeds before they die and drop them,to break the biennual chain,has been my method of controlling that pest.I've noticed though,that GM is usually the first seedlings to emmerge followed by jewelweed,and jewelweed outgrows GM,so I make sure that jewelweed is ubiquitious over my property,especially in areas where weeds are a problem

Garlic mustard cannot out-compete blue fescue, either. Plant some blue fescue, let it grow and die back, then pull it or burn it..the fescue cannot take burning. If you did this a couple years in a row, you would greatly reduce the GM. Solarising is also a great idea, as nywoodsman mentioned above. April

Thought of you,bubbleoffplumb,the other day.While inspecting a newly built stone wall,I noted a large area of bare dirt at its base,potential weed breeding grounds.Near by was a patch of Circaea with ripe seeds ready for sowing.I did the obvious,more obvious after reading your post that is.Thanks