Weeds

Herbicides applied in the fall often can provide improved control of many winter annual weed species compared with similar applications made in the spring. Marestail is one example of a weed species that is often better controlled with herbicides applied in the fall compared with the spring. An increasing frequency of marestail populations in Illinois are resistant to glyphosate, and resistance to ALS-inhibiting herbicides also is present in Illinois populations. Targeting emerged marestail with higher application rates of products such as 2,4-D in the fall almost always results in better control at planting compared with targeting overwintered and often larger plants with lower rates of 2,4-D in the spring.…

Wheat harvest marks the end of one cropping cycle and the beginning of a second. In parts of central and southern Illinois, farmers frequently opt to plant double-crop soybean following wheat harvest, with hopes that the first “killing” frost will be late enough to allow the soybean to reach maturity. Wheat stubble fields not planted with a second crop often become populated with a “crop” of summer annual (and sometimes perennial) weed species. Unlike double-crop soybean,…

A potential scenario of planting delays will be corn planted in fields where no soil-residual herbicide was applied. If the corn has not yet emerged, the soil-residual herbicide can be applied as originally planned. But, what if the corn has emerged and the soil-residual herbicide has not been applied? Can the application proceed as planned, or will a different product need to be selected? The answer depends on the respective herbicide.
Most, but not all, soil residual herbicides can be applied after corn has emerged.…

Soil-residual herbicides are important components of integrated weed management programs. Labels of many single and multiple active ingredient products allow application before and after crop emergence, but other active ingredients can cause severe crop injury if applied to emerging crop plants. In fields where a PRE herbicide application has been delayed and corn or soybean are beginning to emerge, the following active ingredients (applied either alone or as a premix product) or commercial products should not be applied:
Corn
saflufenacil (Sharpen and Verdict,…

The 2022 Weed Control Guide for Ohio, Indiana and Illinois contains 232 pages of weed management information, including weed response ratings for corn and soybean herbicides.  Information and recommendations for managing weeds in small grains and forages are included, along with specific information about, and control recommendations for, several problem weed species.  The 2022 Weed Control Guide is available in pdf or print format and can be ordered at: https://extensionpubs.osu.edu/2022-weed-control-guide-for-ohio-indiana-and-illinois/
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Nearly all herbicide labels (soil-applied or postemergence) have rotational crop intervals that specify the amount of time that must elapse between herbicide application and planting a rotational crop.  This becomes particularly important with late-season herbicide applications, and when soil moisture is limited. Additionally, the labels of almost all postemergence soybean herbicides indicate a preharvest interval or a soybean developmental stage beyond which applications cannot be made.  Labels of some products may indicate both a developmental stage (before soybean bloom,…

The weed science program at the University of Illinois invites all weed management practitioners to our annual weed science field tour on Wednesday, June 23 at the Department of Crop Sciences field research location known as the Clem Farm, located at 1114 County Road 1200 East, Champaign. Registration begins at 7:30 a.m. and the tour will start at 9:00 a.m. Preregistration is not required, but please let us know in advance if you will be bringing a large group of participants so we can plan accordingly for meals.…