What is in this article?:
- Cotton weed control has changed radically due to resistant pigweed
- Comprehensive survey
- Increase in herbicide use
• Surveys conducted by the University of Georgia reveal that monumental changes have occurred in a relatively short amount of time as it relates to cotton weed control practices in response to glyphosate-resistant Palmer amaranth pigweed.
• During this same time, the cost of weed control in cotton production has roughly doubled.
A UNIVERSITY OF Georgia grower and county Extension agent survey reveals substantial changes in weed control practices in response to the development of glyphosate-resistant Palmer amaranth pigweed.
Increase in herbicide use
At the same time, there was a corresponding increase in the amount of glufosinate and metolachlor being used. Similar trends were seen by the county Extension agents who responded.
Growers said post-directed and layby herbicides applied included a decrease in the use of glyphosate while MSMA and diuron stayed about the same.
But there were significant increases in the amount of flumioxazin and metolachlor being used. Agents’ responses were similar, including significant increases in the amount of MSMA and diuron being applied to Georgia cotton acres.
The survey also asked growers how many applications of glyphosate per year were being made. Producers said they were making approximately 2.3 to 2.4 applications of glyphosate per year, both before and after the development of resistant Palmer amaranth.
There was a significant increase in the use of glufosinate for controlling Palmer amaranth. Agents also saw a static number of glyphosate applications but a sizeable increase in the number of glufosinate applications.
Growers are still putting out two applications of glyphosate per year within a crop cycle. However, they might not be placing them on every acre, indicating they may be treating certain fields differently according to the weed pressure.
Looking at costs, growers went from $32 per acre for herbicide weed control to almost $63 per acre. The agents saw an increase of $28 per acre to $68 per acre for herbicide costs.
In 2000 to 2005, 17 percent of growers were hand-weeding 5 percent of Georgia’s cotton acreage at $2 per acre. According to the UGA survey, that has increased to 52 percent of cotton acres being hand-weeded at $24 per acre.
Agents also saw an increase in the amount of acreage being hand-weeded and the associated costs.
The number of acres being subjected to in-row cultivation during the growing season also is increasing.
The survey summarizes that glyphosate-resistant Palmer amaranth is the primary weed problem among Georgia row-crop farmers.
Growers and county agents are reporting similar trends in weed management practices, hand-weeding and cultivation are increasing, glyphosate use — though still high — is decreasing, and at the same time there are increases in the use of other herbicides.
The survey recommends that particular attention be paid to the use of glufosinate, flumioxazin and fomesafen, because of the need to conserve and not over-use, causing more resistance problems.