The University of Illinois Plant Clinic recently published results of their 2016 herbicide resistance screening program. For a $50 fee the Clinic analyzes waterhemp for resistance to both Group 9 (glyphosate) and Group 14 (PPO inhibitor) herbicides. Unfortunately, samples from Iowa displayed a high frequency of resistance to both herbicides (Table 1).
The weed control results from 2015 are now available. The report includes experiments and demonstrations conducted at several of the Iowa State University Research Farms, as well as farmer fields. Highlights include experiments that report on herbicide tactics to control waterhemp with evolved resistance to HPPD inhibitor herbicides and glyphosate-resistant biotypes. If you have questions concerning the report, please contact Mike Owen at 515-294-5935 or mdowen@iastate.edu.
The new 2016 Herbicide Guide for Iowa Corn and Soybean Production publication provides information on product and management updates, the role of preemergence herbicides in glyphosate resistant crops, corn and soybean herbicide effectiveness ratings, and herbicide package mixes.
The spread of herbicide-resistant weeds is a growing problem in many parts of the United States, and the number of weed species with resistance to glyphosate and other herbicides has risen dramatically; contributing to lower yields and profits for farmers.
Crop producers, agribusiness personnel and the general public are encouraged to speak with University Extension personnel before making changes in crop production practices related to glyphosate and glyphosate resistant crops.
Glyphosate resistance was first reported in 1996 from rigid ryegrass in an orchard in Australia. Subsequently, several additional glyphosate-resistant weed populations have been identified: rigid ryegrass in a wheat production system in Australia and in California; Italian ryegrass in Chile; goosegrass in Malaysia; and horseweed (marestail) in the eastern, midwestern, and southeastern United States. The resistance mechanism in goosegrass is due to an altered target site, whereas the mechanism in the other weeds is under investigation.
