Weeds

The long-awaited label allowing dicamba use in dicamba-resistant soybean was granted November 9, 2016, by the United States Environmental Protection Agency (EPA), although only one commercial product received that label.  Many Illinois farmers anticipate this technology will provide a much-needed solution to challenges caused by weed populations resistant to herbicides from multiple site-of-action groups and other difficult-to-control species.  Without question, there are instances and scenarios in which dicamba will improve control of certain weed species, but dicamba will not bring back the “good ol’ days” of POST-only weed control programs in soybean. …

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 recently we confirmed 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.…

Palmer amaranth (Amaranthus palmeri) has garnered much attention recently in both academic discussions and popular press releases, and with good reason.  Among the weedy species of Amaranthus, Palmer amaranth has the fastest growth rate and is the most competitive with the crops common to Midwest agronomic cropping systems.  Soybean yield losses approaching 80% and corn yield losses exceeding 90% have been reported in the peer-reviewed scientific literature.
While most concern focuses on Palmer amaranth in agronomic cropping systems,…

Almost all postemergence soybean herbicides have a preharvest interval or a soybean developmental stage beyond which applications cannot be made specified on their respective label.  Labels of some products may indicate both a developmental stage (before soybean bloom, for example) and a preharvest interval.  Preharvest intervals indicate the amount of time that must elapse between the herbicide application and crop harvest.  Failure to observe the preharvest interval may result in herbicide residue levels in the crop in excess of established limits. …

Waterhemp continues to be one of the most widespread and troublesome broadleaf weed species with which Illinois farmers must contend.  Factors related to the species’ biology, such as prolonged germination and emergence, obligate outcrossing, and high seed production, contribute to management challenges.  The evolution of herbicide resistance in Illinois waterhemp populations adds another very challenging obstacle for effective management.  Recently, many have sent questions and concerns regarding the inability to control waterhemp with various postemergence soybean herbicides. …

We would like to take this opportunity to once again extend the invitation to attend the 2016 University of Illinois Weed Science Field Research Tour, to be held Wednesday, June 29th at the University of Illinois Crop Sciences Research and Education Center, located immediately south of the main campus.  Coffee and refreshments will be available under the shade trees near the Seed House beginning at 8:00 a.m.  The tour will provide ample opportunity to look at research plots and interact with weed science faculty,…

The labels of most postemergence corn herbicides allow applications at various crop growth stages, but almost all product labels indicate a maximum growth stage beyond which broadcast applications should not be made, and a few even a state minimum growth stage before which applications should not be made.  These growth stages are usually indicated as a particular plant height or leaf stage; sometimes both of these are listed.  For product labels that indicate a specific corn height and growth state,…