Source: University of Illinois Extension

Fall herbicide applications have become a relatively common practice for farmers. Much recent interest has focused on applying herbicides after fall harvest to control winter annual weed species, such as common chickweed, henbit and various mustard species. If not controlled before the onset of winter, these and other winter annual species can create dense mats of vegetation prior to spring planting. Controlling these weeds and preventing them from producing seeds are important objectives of fall herbicide applications.

Fall months may offer a good opportunity to apply herbicides for improved control of certain biennial and perennial weed species as well as winter annual species. Biennial and perennial species often become established in reduced-till or no-till fields and can be difficult to control with herbicides once populations are established. 

Original news release