Woolly cupgrass continues to march across the western and northern Corn Belt, largely because it's being controlled like other grasses.
However, Mike Owen, an Iowa State University extension weed scientist, claims the only way to manage woolly cupgrass is to understand that it's not like other grasses.
"The increasing number of acres infested with woolly cupgrass is an example of weed shifts caused by changes in crop management practices," Owen says. "To better manage this weed, we have to adjust management practices."
Woolly cupgrass is different from most grassy weeds in the Midwest in that it's highly competitive and no single strategy provides consistent control. The cost of weed management programs increases once woolly cupgrass becomes established in a field.
Integrating cultural, mechanical and herbicidal strategies improves woolly cupgrass control and helps keep costs at a reasonable level.
One factor that has allowed the weed to spread fast is its high tolerance of most herbicides. Unlike other grassy weeds, like the foxtails, woolly cupgrass can stand high application rates of most older grass-control chemicals. And some of the newer herbicides have very little impact on it.
"The unique biological traits of cupgrass are as important as herbicide tolerance, however, in making it difficult to control," Owen says.
First, woolly cupgrass seed is larger than seed produced by most grassy weeds. It can emerge from soil depths of 4" or more.
Woolly cupgrass seedlings are hardy and usually grow fast. They begin tillering early, at the two- to three-leaf stage, and soon produce seed. This weed is a prolific seed producer, so any plants that escape control quickly replenish the soil seed bank.
The first and heaviest flush of woolly cupgrass typically emerges earlier than giant foxtail. Controlling this primary flush should help diminish the impact of cupgrass on crop yield.
Like most weeds, however, some cupgrass plants will emerge after control strategies have been implemented. Although the percentage of late emergers is lower than with most weeds, late-emerging plants are still able to produce large quantities of seed.
Even though these plants may come in too late to have a significant effect on yield in the current crop, Owen cautions that there could easily be high infestations in subsequent years.
Owen says an integrated strategy would adequately manage woolly cupgrass. It would involve cultural practices like early planting, crop rotation, and row cultivation to supplement timely use of herbicides, as well as constant monitoring of the weed.
The weed is especially difficult to manage in continuous corn. Rotating to soybeans permits the use of herbicides that are more effective on woolly cupgrass than are most corn products.
Alfalfa sometimes is planted to deplete the soil of woolly cupgrass seeds. That usually helps reduce cupgrass populations when a field is brought back into row crops. But sufficient cupgrass seeds will survive to reinfest the field if effective strategies are not implemented.
"The easiest way to manage it is to prevent it from becoming established in a field. Most infestations start from seeds carried into fields on farm machinery," Owen says.
For this reason, he suggests that growers:
* Till and harvest infested fields last, when possible.
* Thoroughly clean implements before moving from infested fields.
* Prevent cupgrass from growing in waterways, fencerows or terraces, all of which are sites where a few escapes can quickly replenish the seed bank.
Plant infested fields as soon as possible after the final tillage pass to give the crop an even start with the cupgrass seedlings.
"A few days' delay between seedbed preparation and plant- ing gives woolly cupgrass a head start on the crop and places the grower at a disadvantage for the remainder of the growing season," Owen says.
Once the crop is up, start managing cupgrass by rotary hoeing the field, he suggests. It will control most emerged seedlings, and also can improve the performance of pre- and postemergence herbicides.
Finally, if timed to suppress the first cupgrass flush, rotary hoeing can provide greater flexibility in application timing of postemergence herbicides.
Row cultivation is less expensive than herbicides and can control cupgrass seedlings between the rows. Herbicides are still needed, though, Owen explains, to remove woolly cupgrass from the rows and to control plants that escape cultivation.