- 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.
Culpepper used a chart with three conjoined circles to explain how growers in the Southeast and other parts of the country are addressing weed resistance – not just in the Palmer amaranth, but in other prolific weeds such as Horseweed, common Ragweed and Ryegrass.
Citing three types of control methods: mechanical, cultural and chemical, Culpepper said growers in his region are not relying heavily on any one method, but are employing strategies in all three methods as equally as possible to be sustainable. Where herbicides once dominated agronomic practices to control weeds, with much less reliance on cultural and even less upon mechanical means of weed control, Culpepper said growers are working hard to equally apply all three methods.
“These practices must become more equalized,” he told his California audience. “Georgia is there now.”
Aside from hand-weeding, Culpepper said growers have also applied mechanical practices to manage weeds that seem to work. The catch there is these types of practices do not fit well with the reduced-tillage methods promoted by the National Resource Conservation Service.
These types of labor-intensive practices are not economically sustainable, Culpepper said. The only reason growers in the Southeast remain economically viable in certain crops is because the price paid for some of the commodities they grow have increased sufficiently to cover these costs, at least for now.
“This has worked for cotton,” he said. “But if we return to 60-cent cotton these guys are done.”
Aside from the triple-pronged approach Culpepper suggests, many researchers during the meeting repeated the same general ideas throughout the conference. Growers need to better understand the weeds growing in their fields and be willing to devote the labor and the resources to reduce the seed banks that these weeds create.
According to Hanson, gone are the days of the $10-per-acre cost of weed control. Once growers cross that hurdle in their minds they can begin to see the value of what Culpepper recommends.
Along that note, Culpepper emphasized the success growers are having in states where there is considerable cooperation between growers and university extension offices. Much success has been seen through the cooperative efforts of growers and researchers through the various land grant universities, he said.
For Albert Fischer, weed science professor in rice from UC Davis, the message is one of label rates. He recommends a strict adherence to the upper limit of label-rate applications, and no more.
Fischer discovered that using not enough herbicides to control weeds leads to the same HRW issues that an over-application will yield.
“This is a catch-22,” Fisher said. “The Europeans discovered this with lower application rates.”
Gene mutations at the molecular level suggest that weeds can more effectively become resistant to chemical applications than when a proper label rate is applied.
Fisher also recommends rotating various modes of action, which means a careful inspection of group numbers when deciding which herbicides to use.
He also recommends staying away from late applications and proper maintenance of spray rigs and sprayer calibrations in order to achieve proper application rates.
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