7. Do not utilize a fall herbicide application as an avenue to provide residual control of summer annual weed species. Control of summer annual species, such as waterhemp, is often improved when applications of soil-residual herbicides are made closer to planting compared with several weeks (or months) prior to planting. If a soil-residual herbicide will be part of a fall herbicide application, select an application rate that will provide control of winter annuals throughout the remainder of 2011, and do not increase the application rate in hopes of obtaining control of summer annual species next spring.
8. With the increasing prevalence of horseweed, including glyphosate-resistant populations, fall herbicide applications may prove more efficacious than spring applications. Glyphosate alone may not provide adequate control when applied in either fall or spring, but a fall application timing provides an opportunity to utilize higher application rates of products (such as 2,4-D) than are feasible to use in spring.
Apart from winter annual weed species, fall months may offer a good opportunity to apply herbicides for improved control of certain biennial and perennial weed species. These species often become established in reduced or no-tillage fields and can be difficult to control with herbicides once the populations are established.