In addition, Hager says location in the state can influence fall herbicide applications. Fall applications seem to “fit” better in areas of central and southern Illinois, possibly due to generally milder average winter temperatures as well as earlier resumption of weed growth in the spring.


“Fall applications that include soil-residual herbicides may not always result in a clean field by planting time next spring,” he adds. “Delays in spring field work may allow the fields to green up before the crop can be planted. Additionally, we have found that if we successfully control the suite of winter annual weed species, the emergence of summer annual weed species (such as common lambsquarters and smartweed) sometimes occurs sooner than if the winter annuals were still present.”


Hager does not recommend using 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 improved when applications of soil-residual herbicides are made closer to planting compared with several weeks (or months) prior to planting. Thus, he recommends selecting an application rate of a soil-residual herbicide that will provide control of winter annuals throughout the remainder of 2010, and do not increase the application rate in hopes of obtaining control of summer annual species next spring.


“With the increasing prevalence of horseweed, including glyphosate-resistant populations, fall herbicide applications may prove more efficacious than spring applications,” Hager says. “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.”