Controlling weeds in continuous corn
Planting continuous corn may promote greater weed control problems, but growers can stave off serious issues as long as they follow the best management strategies for their situation, according to release from Ag Answers, a partnership between Purdue University and Ohio State University.
"Rotation of crops has historically resulted in greater diversity in herbicide use. Planting a monoculture of corn, or even soybeans, can result in greater weed problems over the long term, due to the propensity for overuse of certain herbicides that weeds can become resistant to," says Mark Loux, an Ohio State University Extension weed specialist. "However, we are not convinced that the planting of continuous corn really poses more serious issues for weed management, compared with a crop rotation, as long as appropriate weed management strategies are used."
Loux offers the following considerations for weed management in a continuous corn system to most effectively control tough weeds and minimize selection for herbicide resistance.
- Use tillage or pre-plant burndown herbicides to ensure that corn is planted into a weed-free seedbed
Doing so may help growers avoid issues of glyphosate resistance that have impacted other crop systems.
"Planting soybeans into weedy fields, and delaying the first glyphosate application until sometime after soybeans emerge, contributed to the development of glyphosate resistance in giant ragweed and marestail, and also the general increase in winter annual weeds and dandelions," Loux says.
- Select an herbicide program that is appropriate for the weeds in the field
"A total pre-emergence herbicide program can control many annual weeds, but frequently fails to provide season-long control of weeds that can emerge in mid-season, such as dense annual grass infestations, giant ragweed, burcucumber, and perennial weeds," says Loux. "A combination of pre-emergence and post-emergence herbicide applications is more effective for these type of weeds, and in any field with a history of poor weed control."
- Use a diversity of herbicide sites of action to reduce the risk of herbicide resistance
"This is more easily accomplished where a combination of pre-emergence and post-emergence herbicides are used, compared with a total pre-emergence or post-emergence approach," says Loux. "For example, avoid using atrazine as the sole broadleaf herbicide in continuous corn, and avoid continued use of ALS inhibitors for control of the same weeds every year."
- Use other herbicides in conjunction with glyphosate programs to reduce the chance of glyphosate resistance.
"Apply pre-emergence herbicides at the time of planting to reduce the weed population that will need to be controlled with post-emergence glyphosate applications. In a tilled field where a total post-emergence program is planned, mix glyphosate with other herbicides that can help control emerged weeds and provide residual weed control. And where glyphosate is applied late post-emergence following pre-emergence herbicides, mix it with low rates of other post-emergence herbicides," says Loux.