Fireweed is a summer annual weed that sprouts above the soil in the thatch. Most PreEmergents therefore are basically ineffective at controlling its germination. As you’ve noticed it’s growth is pretty rapid. By fall if left untended the plants reach 10 – 12 ft high. From the top of those plants seed float with wind everywhere during October. I’ve seen lawns with weekly mowing services have far less fireweed in the spring than those that don’t. So, bagging and blowing weekly in the fall will help reduce the number of seed that actually have a chance to begin sprouting in you lawn. When they blow you way and and your lawn begins to look like a turnip patch in May fear not! Post emergents are pretty effective on them. Now one more thing a four inch or higher fireweed plant tell me is, your not mowing weekly! I know. It’s been rainy, the grass isn’t growing so why mow? Fireweed! http://www.walterreeves.com/gardening-q-and-a/burnweed-identification/ One more thing for my friend Stone. Yes you can pull them easily and they work wonders in the mulch pile.