The deliverables from this research were communicated through various methods and individuals throughout the project period. The Purdue Weed Science Field days are held during the last week of June each year. In 2016, we held a field day at our Palmer amaranth site near Medaryville, IN and attendance was nearly 100 people. We held a second field day the same week at a site that contains giant ragweed, glyphosate resistant waterhemp, and glyphosate-resistant horseweed (marestail). We also give presentations at late-summer field days at Purdue Ag Centers, we present data from our summer trials and make recommendations for next year to primarily growers. In 2016, we had over 1,000 people attend these field days and hear our presentations on our herbicide screening and weed management trials. We also summarized the data and presented it in newsletter articles and during private applicator recertification programs (PARP) during the winter Extension meeting season. Each year extension weed scientist Bill Johnson gives presentations in over 30 PARP meetings. Average attendance is 25 to 50 people per meeting. The results were shared at the Purdue University Crop Management Workshops (attendance is approximately 900 people over the course of the 5 day workshop), and the Indiana CCA Convention (attendance is approximately 650 people). The number of acres managed by crop advisers at the Indiana CCA Convention is estimated to be in the millions. Other methods of communicating research results include weekly newsletters during the growing season (Pest & Crop) with over 1,000 subscribers, and Dr. Johnson maintains a website where he can house the results of this work in the form of downloadable decision tools where farmers can evaluate the profitability of a BMP for their operation, and downloadable presentations.

Applied research results are also delivered to growers via the Weed Control Guide for Ohio, Indiana, and Illinois. This multistate endeavor is a 200-page guide that contains concise information for controlling weeds in soybeans, corn, wheat, alfalfa, and forages. This publication is updated annually based on results from our field and greenhouse research programs. In the back of this guide we have special, detailed sections for control of our most problematic weeds.

Update:
refer to uploaded report

View uploaded report

The lab provided a screening service for suspected herbicide resistance in waterhemp, Palmer amaranth, and giant ragweed through the Purdue Plant Diagnostic Lab during the 2016 field season. Waterhemp was the primary weed of concern in 2016 for the samples submitted to our lab for resistance screening, with some giant ragweed samples and no Palmer amaranth samples submitted. Waterhemp was also the most common weed species submitted for resistance screening in 2015, which cements waterhemp as the greatest developing weed resistance problem in Indiana.

Field research experiments designed to identify practices, herbicide products, herbicide strategies, or soybean traits that would improve weed management were conducted on herbicide-resistant waterhemp, giant ragweed, Palmer amaranth, and horseweed (marestail) in 2016. These field trials were conducted by Purdue University and collaborating investigators (Drs. Mark Loux and Aaron Hager) at The Ohio State University and the University of Illinois. Each year, we conduct over 50 trials at these sites and the results are either shared directly with clientele or synthesized and delivered to clientele at numerous venues and through different media outlets (see Communication section below for more details). Some research highlights include: the inconsistency of auxin herbicides (2,4-D and dicamba) for control of glyphosate-resistant horseweed when used as the sole means of control; the importance of application timing for both residual (close to period of peak emergence) and foliar (weed size under 4 inches) active herbicides for all four of these problematic weed species; and the potential for reduced herbicide activity when applying postemergence herbicides with extremely large spray droplets that may reduce spray coverage on target weeds. Overall, the greatest weed challenges arise when the herbicide applications are performed later than desired, as once these problematic weeds gain an advantage it can be nearly impossible to regain control to satisfactory levels for the remainder of the growing season. The results of this field research were delivered through various formats with clientele including the “Take Action” website sponsored by the United Soybean Board and the 2017 Weed Control Guide for Ohio, Indiana, and Illinois, in addition to other outreach activities.

Giant ragweed is among the most competitive summer annual weeds in corn and soybean production. Difficulty in controlling giant ragweed is exacerbated by the evolution of herbicide-resistant (HR) biotypes to both ALS-inhibiting herbicides and glyphosate. Glyphosate resistance (GR) in giant ragweed is unique as there exist two distinct phenotypic responses following application. The rapid response (RR) biotype displays a lesion-causing oxidative burst (rapid necrosis) in mature leaves in as little as two hours after treatment and quickly results in leaf desiccation, thus restricting glyphosate translocation. The non-rapid response (NRR) biotype of giant ragweed exhibits slightly chlorotic leaves and stunted plant growth (similar to glyphosate-resistant marestail response). Both biotypes resume normal growth within a week.
Glyphosate-resistant giant ragweed was found in 36 counties in Indiana compared to only 14 counties in a 2008 survey.