Folks always ask me about wild chervil and garlic mustard, two seed-propagating plant species that tend to colonize woodlines, roadsides, and river corridors. What is the window for control / removal?
I say get after wild chervil all the time, you truly do not want this plant on your property since it’s a bit of a safety hazard for exposed skin. So potato fork it out of the soil in critical chokepoints or gateways and regularly patrol “clean” areas. People worry that they’ve missed their chance once the flowers have formed. Wrong, you still have a couple weeks before the seeds are viable, and after that you have a month perhaps before seeds dry out and shake off. Focus on flowering plants; once you develop some skills you’ll recognize the smaller first-year plants which you can skip over for now. These species operate with the advantage of numbers… so success only comes if we break the seed rain and then limit introduction of new seed.
Nature operates so often with bell curves – there are always early bloomers and late bloomers. So get those of course, and then do the heavy lifting removal work right up until you notice seeds falling or find them sticking to your clothes. You can hear them fall, if you listen. That’s a good time to back off and avoid unintended spreading. Seriously, once they’re ready to fall, the seeds get Everywhere! You’ll notice too that sunny spots are typically ahead of shaded areas, so do the sunny spots first and buy yourself some time. Garlic mustard is tricky in two regards. First, it’ll flower at four feet tall, but also at four inches tall in the same square meter of ground. Then I’ve seen it do a second wave of flowering in late July / early August. So you have to be thorough.
Finally, get after these seed-producing biennials in the fall. That’s when first-year plants are prepping for the next growing season, and until the ground freezes they are easy-picking. Also easy to find, because they tend to remain green. For areas that are too heavily infested to reasonably manage, lay in some sheets of cardboard for a smother effect. Weigh them down and then leave in place through next spring or longer. Just be aware of bio-security… check your clothes and boots. Or better yet, remove the outer layers on site and quarantine these items until you give them a good clean-up.