Herbicide scrutiny mounts as resistant weeds spread in U.S.

By Carey Gillam
Sept 22 (Reuters) - Concerns about the world's most popular
herbicide continue to mount, as U.S. agricultural experts note
spreading weed resistance to glyphosate.
As the key ingredient in Monsanto (NYSE:MON) Co's MON.N Roundup
herbicide products as well as about 700 other products,
glyphosate is widely used on farms as well as residential lawns.
But the chemical has come under increasing scrutiny in
recent years in part because scientists and environmentalists
have warned that weed resistance to glyphosate has become a
significant problem that impacts crop production.
In the latest account of glyphosate-resistant weeds, U.S.
weed scientist Dallas Peterson said this week that resistance
is increasing rapidly in the key farming state of Kansas. The
trend is a worrisome sign as weed resistance spreads from the
southern U.S. into the Midwest and Plains farming states, he
said.
Peterson, who is both a weed scientist at Kansas State
University (KSU) and president of the Weed Science Society of
America, said Kansas soybean farmers in particular are
experiencing weed problems, particularly with a type known as
Palmer amaranth. Wet weather along with the weed resistance
contributed to the problem, he said.
"It's really kind of exploded," he said.
Farmers in other Midwestern states, including Missouri,
Nebraska, and Illinois have reported mounting problems with weed
resistance as well.
Weeds can choke off nutrients to crops hurting production,
and raise costs for farmers who often use added chemicals or
other means to combat the troublesome weeds.
Weed resistance across U.S. farmland is becoming such a
significant problem that the agriculture committee of the U.S.
House of Representatives has scheduled a briefing on the problem
for Dec. 4.
The U.S. Department of Agriculture said that reliance on
glyphosate by many farmers is the primary factor for the
problem. Fourteen glyphosate-resistance weed species have so far
been documented in U.S. crop production areas, according to
USDA.
The use of glyphosate by farmers surged after Monsanto
introduced glyphosate-tolerant "Roundup Ready" soybeans and
other crops in the mid-1990s.
Monsanto and DowAgroSciences, a unit of Dow Chemical
DOW.N , are bringing new herbicides to market, combining
glyphosate with dicamba from Monsanto, and glyphosate with 2,4-D
from Dow.
Peterson warned, however, that tests at KSU showed that
these combinations still had trouble controlling Palmer amaranth
weeds.
Both companies said research shows their new herbicide
combinations are highly effective, but they also advise farmers
to use multiple strategies to fight the troublesome weeds.