"We thought we had a herbicide that was infallible."  - Purdue University weed scientist, Stephen Weller on Roundup

"It's a kind of a symbol of our pest-control policies and our pest-control practices. Our pests are becoming resistant about as fast as we can develop chemicals." - Rae Schnapp, Hoosier Environmental Council
---

Weed develops Roundup resistance
East Coast find will affect farmers' strategies nationwide
BY NORM HEIKENS STAFF WRITER THE INDIANAPOLIS STAR
February 20, 2001

A pesky weed is developing resistance to Roundup in some East Coast farm fields, according to University of Delaware research released last week.

Horseweed, or conyza canadensis, isn't yet known to resist the popular herbicide outside Delaware and New Jersey. But experts say the news will prompt farmers to manage fields differently, and an environmentalist pointed to the discovery as evidence of wrong-headed thinking.

"It's a kind of a symbol of our pest-control policies and our pest-control practices," said Rae Schnapp of the Hoosier Environmental Council. "Our pests are becoming resistant about as fast as we can develop chemicals."

However, John Goette of Monsanto, the St. Louis company that developed the herbicide, defended the weed killer as comparatively benign. "We have only two resistant plants after one quarter century" of use, Goette said.

Initial Monsanto tests show horseweed with elevated resistance, but not as much as the university's findings, Goette said. Ryegrass in Australia and goosegrass in Malaysia developed resistance in the late '90s.

Delaware farmers last summer complained of horseweed surviving Roundup treatments in soybean fields.

Seeds gathered from the surviving weeds were germinated in green houses. Then the plants were doused with as much as 10 times the amount of Roundup typically used in fields.

They lived. Said University of Delaware researcher Mark VanGessel, "I knew we had something unusual."

It is the first broadleaf weed to resist glysophate, the active ingredient in Syngenta's Roundup and Touchdown.

Nearly two-thirds of soybeans grown in Indiana are resistant to Roundup. Farmers in the 1990s had enthusiastically adopted soybeans genetically engineered to survive Roundup because the chemical conveniently killed everything but the soybeans.

VanGessel emphasized the resistance resulted from stronger plants surviving, not genes shifting from genetically altered crops to the weed.

Farmers have long used Roundup along with other chemicals to "burn down" weeds before planting. The other chemicals probably suppressed horseweed even as the stronger specimens developed Roundup resistance.

When farmers switched to Roundup-resistant soybeans and abandoned the  other chemicals, the horseweeds suddenly survived.

Referring to early Monsanto claims and farmer hopes, Purdue University  weed scientist Stephen Weller said, "We thought we had a herbicide that was infallible."

Horseweed resistance will come slowly in Indiana, because different herbicides are rotated along with crops, Weller said.