- Glyphosate resistance continues to generate concerns for growers and chemical companies
- University of Georgia researcher recommends multi-faceted weed management approach
California rice heavily impacted by resistance issues due to its monoculture
Herbicide resistant weed issues continue to be studied by weed scientists. Speaking at the recent California Weed Science Society meeting in Monterey were, from left, Albert Fischer, weed scientist, UC Davis; Brad Hanson, cooperative extension weed specialist, UC Davis; and Stanley Culpepper, professor and extension agronomist, University of Georgia.
Rice in California is the most affected crop in terms of weed pressure and resistance issues, though glyphosate resistance is not one of them. Multiple resistance issues in rice are very concerning to researchers and growers alike, he said. Hanson showed a slide with 14 different weeds within rice systems that are confirmed to be resistant to various modes of action.
HRW issues in rice have been around since the 1990’s, he said. Currently about 75 percent of California rice fields have some sort of HRW issue, according to Hanson.
The problem in rice is that it is a very herbicide-reliant system with only a few modes of action available, Hanson said. Moreover, rice is part of a monoculture system that is not rotated into other crops, which only aids the problem.
Hanson expects more HRW issues to pop up in the coming years as researchers identify new weed species that can survive multiple chemistries.
Stanley Culpepper, professor and extension agronomist with the University of Georgia, also sees confirmed cases of HRW on the rise, but non-confirmed cases seem to be equally troubling as research suggests more cases will be confirmed in the near future.
“The dominant resistant weed in the Southeast is Palmer amaranth,” Culpepper told the CWSS audience. “It is very drought resistant and will grow two-to-three inches a day.”
Culpepper said growers in his region seem to be making headway in attacking the problem, but not without cost.
“They’re still getting the production, but it’s more costly to get that production,” Culpepper said.
In one example, Culpepper said a grower in the Southeast was forced to hand weed his fields in order to remove the weeds and control the seed bank these weeds create when they go to seed. Photos showed workers stacking weeds on large flatbed trailers to be hauled out of the field.