LINCOLN, Neb. -- As with most things in life, too much of anything rarely is a good thing.



That saying also holds true when it comes to the use of glyphosate, a popular non-selective herbicide.



After a year of testing, University of Nebraska-Lincoln research confirmed marestail, also known as horseweed, is resistant to glyphosate. This is the first glyphosate-resistant weed to be confirmed in the state, UNL weed scientists say.



Weed resistance usually results from repeated use of the same herbicide, said Steven Knezevic, integrated weed management specialist at the university's Haskell Agricultural Laboratory near Concord. Widespread use of glyphosate herbicide has resulted in selection pressure on weed populations in recent years.



"Prior to the introduction of glyphosate-tolerant crops only a few weed species -- ryegrass and goosegrass -- had developed resistance worldwide," he said. "However, the number of glyphosate-resistant weeds tripled in just over eight years of repeated glyphosate use due to the introduction of Roundup Ready crops."



Other glyphosate-resistant weeds in the U.S. include waterhemp, lambsquarters, giant ragweed, common ragweed and palmer amaranth.



"We believe that glyphosate- and herbicide-tolerant crops, including those based on glyphosate herbicide, can remain useful components of crop production systems only with proper management," said Alex Martin, UNL weeds specialist. "It is easy to fall into a trap of overusing glyphosate versus combinations of pre-emergence herbicides or tank mix partners when one Roundup Ready crop is grown after another."



This makes proper use of herbicide tolerant technology an important component of an integrated weed management program to preserve the long-term benefits of this technology and concerns of its use or misuse, Martin said.



For more information about glyphosate-resistant marestail being confirmed in Nebraska, visit Crop Watch, extension's crop production newsletter.

For more information about glyphosate-resistant crops, consult UNL Extension NebGuide G02-1484-A, Use of Herbicide Tolerant Crops as a Component of an Integrated Weed Management Program, or the UNL Extension Circular EC130, Guide for Weed Management in Nebraska Both are available at local extension offices.



SOURCE: University of Nebraska news release.