Weeds

The continual evolution of weed species and populations resistant to herbicides from one or more site-of-action groups represents one of the most daunting challenges facing Illinois soybean producers. Waterhemp has evolved resistance to herbicides from more site-of-action groups than any other Illinois weed species, including resistance to Group 15 herbicides (products such as Dual II Magnum, Zidua, Warrant, Outlook, etc.). Soil-residual herbicides are components of an integrated weed management program that provide several benefits, including reducing the intensity of selection for resistance to foliar-applied herbicides.…

 
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 28 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.…

One of the most daunting challenges facing agronomic crop production is the continuing evolution of weeds resistant to herbicides. The magnitude of herbicide resistance is best measured on a global scale. The most recent summary indicates 520 unique cases of herbicide resistance—encompassing 268 species—occur globally. Approximately 11–12 cases of unique resistance are discovered each year. In contrast, our understanding of how and why weeds are evolving various resistance mechanisms is evolving much slower. This introduces a somewhat precarious situation: if we do not fully understand how/why these resistance mechanisms evolve,…

Dry soil conditions across many areas of Illinois have contributed to accelerated crop planting. It is a bit unusual at this point in the season that such a high percentage of corn and soybean acres already have been planted. Soon, postemergence herbicide applications will begin. However, one potentially adverse consequence of very dry soil is the often large amount of dust propelled into the air by either application equipment or high winds.
Airborne dust has been shown to reduce the activity of some foliar-applied herbicides,…

While conditions during much of April were conducive for planting, these same conditions were NOT conducive for good performance of soil-residual herbicides. Many surface-applied herbicides received neither timely precipitation nor mechanical incorporation to move the applied herbicide into the soil solution. Herbicide effectiveness can be significantly reduced when a soil-applied herbicide is sprayed on a dry soil surface with no incorporation (mechanical or by precipitation) for several days following application. The amount of precipitation required to move the herbicide into the soil and how soon after application the precipitation is needed are difficult to define and can vary by herbicide,…

Soil-residual herbicides are important components of integrated weed management programs.  Reducing the number of weeds exposed to foliar-applied herbicides helps reduce the selection intensity for weeds to evolve resistance to foliar-applied herbicides. Residual herbicides applied with postemergence soybean herbicides also can reduce the need for a second postemergence application. However, simply applying a soil-residual herbicide does not guarantee the product will provide the desired level or duration of weed control. Many edaphic and environmental factors influence the level of weed control achieved by soil-residual herbicides.…

A potential scenario encountered each growing season is 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.…

The weed science program at the University of Illinois invites all weed management practitioners to our annual weed science field tour on Wednesday, June 28 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.…

Pest management practitioners will increasingly find changes to many pesticide labels as the United States Environmental Protection Agency (EPA) begins to implement requirements mandated by the Endangered Species Act (ESA). We encourage all who are involved in pest management disciplines (farmers, applicators, scientists, etc.) to become more familiar with the ESA and how the EPA proposes to meet the agency’s requirements under ESA when registering or reregistering pesticides.
Dr. Lee Van Wychen is the Executive Director of Science Policy for the Weed Science Society of America (WSSA).…