Improving Weed management by Addressing Faulty Herbicide Application Methods and Herbicide-Resistant Weed Bio Types
Sustainable Production
Field management Nutrient managementSoil healthTillageYield trials
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Bryan Young, Purdue University
Co-Principal Investigators:
Bill Johnson, Purdue University
Project Code:
Contributing Organization (Checkoff):
Institution Funded:
Brief Project Summary:

Wide-scale adoption of glyphosate-resistant soybean has transformed the way many growers manage weeds. Initially, the use of glyphosate essentially removed weed management as a major challenge for soybean producers, including those weeds already resistant to previous herbicide modes of action. However, the persistent use of glyphosate has resulted in widespread weed resistance to glyphosate in waterhemp, Palmer amaranth, giant ragweed, and horseweed across Indiana. The research aims to improve weed management in soybean by characterizing the extent of herbicide-resistant weed biotypes in the Indiana landscape, developing management strategies for problematic weeds, and discerning methods to optimize the performance of foliar herbicide applications.

Key Benefactors:
farmers, ag retailers, applicators, agronomists

Information And Results
Final Project Results

See attached report

View uploaded report PDF file

Waterhemp was the primary weed of interest in 2015 for the samples submitted to our lab for resistance screening. Of the waterhemp plant samples submitted 61% were resistant to PPO-inhibiting herbicides, 80% were resistant to ALS-inhibiting herbicides, and 65% were resistant to glyphosate. Furthermore, 36% of the plant samples contained multiple resistance to glyphosate, PPO, and ALS herbicides. The primary counties from which the samples were submitted were from Gibson, Vanderburgh, and Warrick counties in the southwestern part of Indiana. Current maps for the most problematic herbicide-resistant weeds are provided below.

Field trials were established to determine the best strategy for management of glyphosate-resistant horseweed (marestail) in regards to fall versus spring herbicide applications. Furthermore, different herbicides with varying levels of soil residual activity were also evaluated. Arguably, most of the problems arise when farmers implement their first herbicide application too late. Thus, fall or very early spring application of herbicides with soil residual are justified in best management practices for horseweed in Indiana. Information from this project has been incorporated into a fact sheet entitled “Control of Marestail in No-Till Soybean” which was released in Fall 2015.

During this project we have tested new formulations of dicamba and glyphosate; 2,4-D choline plus glyphosate at different water temperatures, solution holding duration, pH, hardness, co-applied foliar fertilizers, and water conditioning adjuvants. Herbicide spray solution storage time (= 24 h after mixing herbicide) did not affect the efficacy of premixed of dicamba plus glyphosate; 2,4-D choline; glufosinate; or mesotrione on giant ragweed, horseweed, Palmer amaranth, and pitted morningglory. In some instances, extremely cold or hot water temperatures did reduce herbicide efficacy which should be considered in early spring and late fall herbicide applications, or when water is stored in above-ground tanks for extended periods during the heat of the summer. Results of the research was summarized in a new publication from Purdue this summer (Devkota P, Whitford F, Johnson WG, Young B, Legleiter T, Smith KL (2016) Water Temperature and Herbicide Performance. Purdue Extension. PPP-112).

There was no interaction between carrier water pH and hardness on 2,4-D choline or premixed dicamba plus glyphosate efficacy for weed control. However, the effect of carrier water pH or hardness was observed on herbicide efficacy. This research illustrates that carrier water pH or hardness is critical for 2,4-D choline and premixed dicamba plus glyphosate application; therefore, carrier water should be at acidic pH and free of hardness cations for achieving optimum performance from these herbicides. However, commercial concerns of an increased risk of dicamba volatility at the lower spray pH range may prevent the optimization of dicamba plus glyphosate combinations by adjusting spray pH.

The addition of ammonium sulfate (AMS) resulted in greater efficacy of 2,4-D choline, premixed 2,4-D choline plus glyphosate, glufosinate, and mesotrione for giant ragweed, horseweed, and Palmer amaranth control. Therefore, carrier water pH, co-applied foliar fertilizer, and water conditioning adjuvants have the potential to influence herbicide performance; however, herbicide chemistry and formulation, and weed species could play a role in the differential response of these factors on herbicide efficacy

A significant portion of corn and soybean growers do not perform routine tests on spray water quality. Our research highlights the importance of water quality on herbicide performance and applicators should consistently test their water supplies and make the appropriate adjustments to optimize herbicide activity, yet be cognizant of any potential disadvantages such as the potential for greater dicamba volatility with spray pH below 5 or 6. Failure to optimize foliar herbicide applications have and will continue to encourage the evolution of herbicide-resistant weeds.

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.