Trying to get a handle on weeds

URBANA, Ill. – Herbicides are designed to selectively kill weeds in crops. At the same time, it is difficult for most herbicides to selectively control weeds that are closely related to certain major crops, such as grass weeds in corn and wheat and broadleaf weeds in soybeans and cotton.
Understanding the science. To overcome this problem, chemical compounds known as herbicide safeners are commonly used with herbicides to protect corn and other grass crops from injury. Although these chemicals are included in most major soil-applied herbicides for corn, the details of how and why they work are still not well understood.
As part of a project under way at the University of Illinois, a research team headed by Dean Riechers, assistant professor of weed physiology, is studying the mechanisms of how safeners protect plants from herbicide injury.
Studying safeners. “Chemicals known as safeners are like plant vaccines that can immunize a crop against herbicide injury,” Riechers said.
They are used in most herbicides for corn, such as Dual II Magnum, Bicep, and Harness Xtra.
“By understanding what is going on at a molecular level, we hope to someday develop plants that can effectively treated by herbicides without the added safener.”
What triggers defense? Current work is focused on studying the proteins and genes that are induced by herbicide safener treatments in different tissues of wheat seedlings.
The seedlings can also serve as a model for understanding how and why safeners work inside corn and other grass-related crops.
“Our research indicates that safeners trigger the expression of proteins in a plant defense pathway that is normally regulated by a plant hormone called jasmonic acid,” Riechers said.
“This pathway is usually stimulated in response to insect feeding or by other types of stress. It appears that herbicide safeners can also induce the proteins and genes involved in this stress response within a plant’s defense pathway.”
Broadleaf differences. Riechers’ research team is also studying the perplexing question of why safeners do not protect broadleaf crops, such as soybeans and cotton, from herbicide injury.
“Our research shows that this may be due to differences in the tissues of emerging grass and broadleaf seedlings,” Riechers said. “This could well be the key to figuring out why they respond differently to safeners.”
He notes that much of the information gained from studying the response to safeners in cereal crops could also be applied to understanding the problem in broadleaf crops. Such information could eventually be used to introduce the safener response into a crop such as soybeans.
“That would allow the use of herbicides that are not registered for use in soybeans due to unacceptable crop injury,” Riechers said.
“We could then expand the number of weed management options for controlling resistant or difficult-to-control weeds, such as waterhemp and lambsquarters.”