American burnweed, also known as fireweed, is a summer annual that commonly grows in cultivated areas. It tolerates modern shade and requires moist soil in which to flourish. This weed grows quickly and stands erect as it grows, producing white or green flowers in clusters. The seeds have parachutes and disperse in the wind, landing in open areas and taking root in the thatch layer on lawns.
Because American burnweed seeds germinate in thatch, it's difficult to treat this lawn pest with pre-emergent herbicides. If you want to prevent germination, it's best to keep your lawn mowed at a short height below the weed's growing point. In addition, applying a postemergent herbicide will kill the weeds and keep them from producing seeds and spreading to other parts of the lawn.