Weeds

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).…

The United States Environmental Protection Agency (US EPA) issued new state-specific application restrictions for dicamba-containing products labeled for use in Illinois dicamba-resistant soybean varieties. The three dicamba products (i.e., XtendiMax, Engenia, Tavium) cannot be applied after June 12 or the V4 soybean growth stage, whichever comes first. We remind applicators these new restrictions are in addition to the existing application restrictions imposed by the Illinois Department of Agriculture that include:

1. A pesticide containing dicamba shall not be applied on soybeans if the air temperature at the field at the time of application is over 85 degrees Fahrenheit or if the National Weather Service’s forecasted high temperature for the nearest available location for the day of application exceeds 85 degrees Fahrenheit.

…

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,…