In a 2005 survey conducted by weed scientists in six states, only 30 percent of agricultural producers believed that weed resistance would ever evolve into a serious problem.
Five years later, glyphosate-resistant biotypes have developed in Palmer pigweed, giant ragweed, Italian ryegrass, johnsongrass and others.
To combat the problem, producers are becoming reacquainted with residual herbicides, tillage, hooded sprayers and even hand hoeing. Most realize that if resistant weeds are left unattended, it can put them out of business in a heartbeat.
It has become a very serious problem. As Tennessee weed scientist Larry Steckel pointed out recently — the days of total postemergence weed control in cotton are over.
Of course, this doesn’t mean that glyphosate isn’t still a valuable tool. “It’s still controlling a lot weeds,” said David Jordan, a weed specialist at North Carolina State University. “It’s important that we work to sustain that system and make sure that dominant weeds like Palmer pigweed don’t minimize the effectiveness of glyphosate on the other four or five weeds that might be in the field.”
There is also the importance of stewardship in maintaining those programs — and not just for the obvious reasons. “If problems continue to increase as they have for the last couple of years, will there be some type of regulatory intervention on programs?” Jordan said. “No one really wants to go down that road.”
Producers may point out that protecting herbicide-resistant technologies is a drain on their bottom line. When resistant weeds aren’t in the field, implementing a resistance management plan is an even more difficult decision to make.
But what if it turned out that resistance management could actually improve a grower’s bottom line? Jordan and other researchers at NCSU are working on a research project in cotton what indicates it might. The project was funded by Monsanto.
Eight growers cooperated in the study, conducted in North Carolina by university researchers. Grower fields were split in half. On one side, the grower used his traditional herbicide program to control weeds. On the other side, researchers put in a program in which weed control “was turned up a notch” in terms of the number of residual herbicides used. When the study was initiated, there were no resistant weeds in the fields.
Over three years of the study, weed control costs averaged about $20 per acre more on the research side, but yields averaged 112 pound more per acre. Net income for the research side increased by $40 an acre over the grower side in 2006, $50 an acre in 2007 and $75 an acre in 2008.
What is also interesting is that glyphosate-resistant Palmer pigweed showed up on the grower side in 2008, but so far, resistance has not been observed on the research side of the fields. If you’re in the process of retooling your weed control program, this study might be one to keep an eye on.