Herbicide resistance in weeds has been around for over 25 years, but we continually hear more about it, particularly from the continuous use of glyphosate products, such as Roundup. While crop rotation is usually a recommended cropping practice, it will not necessarily help reduce the problem of herbicide resistance. Now with the increased use of Roundup Ready soybeans and corn, there is increasing concern for resistance to build up in weeds to (Roundup) glyphosate.

The University of Nebraska-Lincoln confirmed glyphosate resistant marestail from fields in eastern Nebraska. This weed is common all across our region, particularly in no-till fields. Farmers have burned down weeds in fields with Roundup year after year, increasing the potential for resistance to develop.

There is also been confirmed glyphosate-resistant giant ragweed in Nemaha and Richardson Counties in southeast Nebraska. This weed has been difficult to control after multiple applications of glyphosate at a site in southeast Nebraska.

There has also been glyphosate-resistant waterhemp confirmed by the University of Missouri-Columbia, in northwest Missouri, which isn’t very far from here either.

A weed that is present in Nebraska that has developed glyphosate-resistance in Southern states is Palmer Amaranth. It is present in Missouri from Kansas City to the Iowa border. While I have not seen it in southeastern Nebraska, there is definitely a good chance that it is here with it being confirmed just across the river in Missouri. Palmer Amaranth is very competitive and can grow up to 2-3” per day under good growing conditions. With this aggressive weed so close to our region, there is definite concern if it develops resistance. Where glyphosate-resistant Palmer Amaranth has developed in the South, it is requiring 3-4 additional herbicide applications which really increase production costs in corn and soybeans.

Farmers in southeast Nebraska also are concerned about glyphosate-resistant waterhemp. A major concern is stacked resistance, especially in water hemp. This is when weeds, such as waterhemp are resistant to a number of herbicides, i.e. triazines, ALS, glyphosate, even 2,4-D.

There is a workshop scheduled for March 19, from 9 a.m. to noon at the 4-H Building on the Nemaha County Grounds in Auburn.

At this workshop you can learn what you can do now to stop the increase of herbicide-resistant weeds in southeast Nebraska. This “hands-on” workshop will demonstrate how to use the Herbicide Site of Action Numbering System in the 2013 Guide for Weed Management Guide for Nebraska and cover these topics:

• herbicide tolerant crops,

• how weed resistance develops,

• overview of weed resistance in the Midwest and Nebraska, and

• examples and practical solutions for major weed resistance cases in Nebraska.

On-line preregistration is required. To preregister go to: http://cropwatch.unl.edu/web/cropwatch/archive?articleID=5098902 and you will find instructions for registration for the workshop. Cost is $30 and includes a variety of printed materials to use for later reference. Doors will open at each site at 8:30 a.m. local time and the meeting will be held from 9 a.m. to noon. Register early as attendance will be limited to 30 people per site in order to facilitate the hands-on format of these workshops. If you do not have computer access and are interested in this workshop, please contact us at the University of Nebraska-Lincoln Extension office in Auburn at (402) 274-4755 and we will assist you in the preregistration process.