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 within the past year we have confirmed that resistance to ALS-inhibiting herbicides also is present in Illinois populations. …

Accurate identification of weedy Amaranthus species during early vegetative stages can be difficult.  However, identification of the various species becomes much more reliable when reproductive structures are present (Figure 1).
Before harvest begins, consider taking a few minutes to scout fields; at this time of year it is much easier to differentiate between Palmer amaranth (Figure 2) and waterhemp plants (Figure 3).
Similar to waterhemp, Palmer amaranth plants are either male or female; male plants produce only pollen while female plants produce only seed. …

The weed science program at the University of Illinois would like to take the opportunity to remind everyone of the Palmer amaranth field research tour scheduled to begin at 9:00 a.m. on July 30.  The tour will feature presentations about Palmer amaranth identification, biology, and management and provide participants the opportunity to view several field experiments conducted by the University of Illinois and scientists from Bayer CropScience.  Advanced registration can be accomplished by visiting bayerrespecttherotation.com. …

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.  Adhering to these intervals is always important, but becomes particularly important with late-season herbicide applications or when soil moisture is limited.  These intervals are established to reduce the likelihood that herbicide residues will persist in sufficient quantities to adversely affect the rotational crop.  Some herbicide rotational restrictions are based solely on time,…

The University of Illinois weed science program would like to extend an open invitation to join us on July 30, 2014 for a field tour and discussions at our Palmer amaranth research site, located approximately ½ mile east of the intersection of county roads 14000 west and 3000 north (see Google map following this article) near the community of Union Hill.  The tour will provide an excellent opportunity for farmers, input suppliers, members of the media,…

Herbicide-resistant waterhemp populations continue to expand into more areas of Illinois each season.  Waterhemp has evolved resistance to herbicides encompassing more mechanisms of action than any other Illinois weed species, including resistance to inhibitors of acetolactate synthase (ALS), photosystem II (PSII), protoporphyrinogen oxidase (PPO), enolpyruvyl shikimate-3-phosphate synthase (EPSPS) and hydroxyphenyl pyruvate dioxygenase (HPPD).  Not every individual waterhemp plant is resistant to one or more herbicides, but the majority of field-level waterhemp populations contain one or more types of herbicide resistance. …

We would like to take this opportunity to once again extend the invitation to attend the 2014 University of Illinois Weed Science Field Day, to be held next Wednesday, June 25th 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,…

Accurate identification of weedy Amaranthus species during early vegetative stages sometimes can be difficult.  Differentiating between smooth pigweed and waterhemp is relatively easy since one species (smooth pigweed) has pubescence on the stem and leaves while the other does not.   However, differentiating between waterhemp and Palmer amaranth during early vegetative stages can be much more difficult.  To assist weed management practitioners in accurately identifying Palmer amaranth, we will accept tissue samples from suspected Palmer amaranth plants and use tools of molecular biology to identify whether the plant is Palmer amaranth or another species of Amaranthus. …

Integrated weed management programs offer the greatest potential for long-term, sustainable solutions to weed populations demonstrating resistance to herbicides from multiple families.  Soil-residual herbicides are important components of integrated weed management programs and provide several benefits, including reducing the intensity of selection for resistance to foliar-applied herbicides.  Recent survey data indicate the percentage of Illinois soybean acres treated with soil-residual herbicides has increased during the past few years.
In the vast majority of instances, soil-applied herbicides control target weed species with little to no adverse effect on the crop. …