Although Roundup-tolerant soybean varieties will provide an important new weed management tool for Arkansas soybean producers, some farmers may take an "if-it-ain't-broke-don'tfix-it" approach.
"If the weed control program a farmer is using is doing a good job at a low cost, he might not want to change," says Dr. Dick Oliver, an agronomy professor in the University of Arkansas Dale Bumpers College of Agricultural, Food and Life Sciences.
If the weed control program a farmer is using is doing a good job at a low cost, he might not want to change.
Factors that would figure into the farmer's decision include availability and price of Roundup-tolerant seed, variety selection and the price of existing herbicides.
Whichever system a producer prefers, he or she should keep in mind that rotating Roundup with existing herbicides will reduce the risk of weeds developing herbicide resistance, Oliver said.
Existing herbicides can be used for effective soybean weed control at a cost of $10 to $15 per acre, or even less, using Cooperative Extension Service guidelines for careful timing of reduced-rate herbicide applications.
The reduced rate recommendations developed by Oliver and weed scientist Dr. Ford Baldwin, state leader of the Extension pest management section, were first published in 1985 in the annual Extension publication MP-44, Recommended Chemicalsfor Weed and Brush Control, and in the "Soybean Weed Control" computer program.
Arkansas Soybean Promotion Board research grants have helped support continuing studies to verify and update reduced rate recommendations and other soybean weed control research.
Weed biology research, also supported in part by the Arkansas Soybean Promotion Board, is providing information that will be needed regardless of the farmer's choice of herbicide chemistry, Oliver said.
"An understanding of weed biology and ecology will allow effective timing of cultural and chemical control practices," he said. "A key component of a weed management program is the assumption that the producer can manage the weed seed bank or weed seeds produced when complete control is not obtained."
Extensive weed seed bank information is not currently available, especially for hard-tocontrol weeds, he said.
Field experiments under tilled and no-tilled conditions are being conducted to learn more about important questions such as percent of weed seeds that emerge the following year, the percent that remain viable in the soil, and the effects of environmental conditions such as temperature and moisture.
"These are critical considerations for determining effective timing and rate of herbicide applications," Oliver said. He added that information on weed emergence patterns will also help in planning planting dates to avoid major weed emergence flushes.
