Weeds

Recently, the weed science program at the University of Illinois published recommendations for the management of Palmer amaranth in Illinois agronomic crops.  One particular recommendation emphasizes the need for timely application of foliar-applied herbicides; in particular, foliar-applied herbicides must be applied before Palmer amaranth plants are taller than four inches.  Most weed management practitioners are very familiar with the growth rates of waterhemp and many other weed species, but perhaps are less familiar with the growth rate of Palmer amaranth.…

The number of acres in Illinois seeded with various cover crops has increased during the past few seasons.  Those cover crops that do not winter kill are usually controlled the following spring with herbicides.  Dr. Bob Hartzler, extension weed scientist at Iowa State University, recently published an excellent article in which he describes several factors that can impact the performance of spring-applied herbicides used to terminate cover crops.  We sincerely appreciate Dr. Hartzler’s willingness to allow us to reproduce his article which follows.…

Palmer amaranth is a weed species that must be thoughtfully and carefully managed; simply attempting to control Palmer amaranth often leads to ineffective herbicide applications, substantial crop yield loss, and increasing weed infestations.  Ignored or otherwise not effectively managed, Palmer amaranth can reduce corn and soybean yield to near zero.  The threat of Palmer amaranth during the 2014 growing season is very real across a large portion of Illinois.
In January 2014, the weed science program at the University of Illinois developed recommendations for management of Palmer amaranth in agronomic crops. …

Widespread and often very dense populations of marestail in soybean fields last spring caught the attention of farmers and other weed management practitioners.  Many came to the difficult realization that marestail is not a problem weed species only in the more southern portions of Illinois.  It’s difficult to say with complete accuracy how far north these infestations occurred, but mature marestail was easily observed during recent travels through Kankakee and Will counties.  As we mentioned earlier this year,…

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.  Palmer amaranth can be effectively managed in Illinois agronomic crops,…

Recently, we have identified populations of Palmer amaranth in several Illinois counties.  The density of many populations is relatively low, and often these plants occur only in small patches.  However, a few scattered plants this year can lead to severe infestations within only a few years.
We continue to accept tissue samples from suspected Palmer amaranth plants and use tools of molecular biology to identify whether the sample is Palmer amaranth or another species of Amaranthus. …

The volume of inquiries about how to control large (taller than 12 inches) horseweed (a.k.a. marestail) and waterhemp in soybean has remained consistent over the past 10 days.  The answer can be summarized as follows: there are NO postemergence herbicides that will consistently control these very large weeds in soybean, especially if these weeds are resistant to glyphosate.
Glyphosate-resistant waterhemp can be controlled by foliar-applied PPO inhibitors (such as lactofen (Cobra), fomesafen (Flexstar) or acifluorfen (Ultra Blazer)) in conventional or glyphosate-resistant soybean varieties,…