Weed Resistance Increases Production Costs

Reduced yields and increased production costs associated with weeds resistant to one or more herbicides, including glyphosate, is a growing concern among producers and industry leaders, according to "Nature Finds a Way," a report released Tuesday by researchers at Rabobank International Food and Agribusiness Research and Advisory.
Waterhemp is among the 13 weed species with resistance to glyphosate that have been confirmed in the U.S. (DTN photo by Pam Smith)
"The prevalence of herbicide-resistant weeds is increasing at a rapid rate throughout the United States," said Sterling Liddell, Rabobank vice president of food and agribusiness research, in a phone interview. "The problem with weed resistance is you don't know it's a problem until it's a serious problem."
Soybeans and cotton are most susceptible to the rising costs because they have fewer chemical options for controlling key weeds, which are developing resistance to multiple herbicides.
The report estimated soybean farmers in the South, who have experienced the most weed resistance in the U.S., spend $40 to $45 more per acre to control weeds. Farmers in the southern Corn Belt are paying $30 more per acre, and areas that are still in the preventive mode in the northern Corn Belt have increased production costs of $10 to $15 per acre.
Larry Steckel, University of Tennessee extension weed specialist, told DTN he expects much higher production costs in Southern cotton. "In cotton, costs are well over $100 an acre; that is not sustainable. We are going to have to turn this around somehow. We won't be growing cotton if we have to throw that much herbicide at it."
Soybeans with glyphosate resistance were introduced in 1996. The new technology allowed soybean farmers to spray Roundup on soybeans for complete weed control and cut down weed management costs significantly. Within five years of wide adoption of the system a population of resistant weeds was identified.
By 2011, 13 weed species with resistance to glyphosate were confirmed in the U.S., including horseweed, Palmer amaranth, common waterhemp, giant ragweed, common ragweed, Italian ryegrass, Johnsongrass, kochia, annual bluegrass, goosegrass, hairy fleabane, jungle rice and rigid ryegrass.
There were more than 85 confirmed biotypes -- weed types within a species -- observed in 28 states. Of those, 15% were resistant to more than one mode of action (MOA).
"As weeds become resistant to multiple herbicides, you start to lose the important tools that farmers have had in the past to deal with weeds," Liddell said. "This is a serious issue if we start to lose the efficacy of some of these critical herbicide products."
Expansion of glyphosate-resistant weeds is predicted to be explosive within the next three years. Poor weed control this spring, due to lack of rainfall to activate pre-emergence herbicides, could make 2012 a critical season, resulting in forced changes in farming practices and culture. More than 90% of the 2012 U.S. soybean acreage is planted to glyphosate-resistant varieties.
True diversity in both chemical and production management programs that include frequent rotation of herbicide classifications, effective crop rotation and increased tillage will be required to prevent weed infestation that can decrease yields by up to 17% to 20%, the Rabobank report said.
Farmers are not only using additional herbicides, many are relying on spot tillage in certain areas and even hiring hand cultivators to cut weeds out of the fields.
Jim Carroll, a soybean and cotton farmer from Brinkley, Ark., plans to begin hand cultivating his soybean fields next week for the second consecutive year. Before 2011, he had not hand cultivated since the 1970s when it was a common practice in cotton fields. Hand cultivation was the best option when Palmer amaranth became a problem in his fields after the 2008 floods.
Palmer amaranth can grow two to three inches a day during this time of year. The herbicides currently being used aren't effective on Palmer amaranth taller than three inches, Steckel said.
Based on farmer and weed scientist interviews, resistance problems often occur in a few fields with more relaxed management standards before spreading, according to the report. Implementing preventive measures and understanding local conditions will be vital for a good weed management program.
Pending regulatory approval, new soybean genetics based on a glyphosate platform with a dual resistance to active growth regulator ingredients (2-4D and Dicamba) are expected to be released on the market in 2014 to 2015.
Lindsay Calvert can be reached at lindsay.calvert@telventdtn.com


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