New weed resistant to Roundup® at 16x the label rate!

[Craig Dremann]

Dear All,

Here's a press release about a weed, Conyza bonariensis or Hairy
Fleabane, with a newly discovered extreme resistance to Roundup®.  

Originally native to South America and common in agricultural areas of
California, some populations can't be killed at 16x the application rate
on the label! 

Sincerely,  Craig Dremann (650) 325-73333

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>>> "UC ANR News" <ucanrnews at ucop.edu> 09/06/07 14:17 >>>
September 6, 2007

CONTACT: Stephanie Klunk, (530) 754-6724, sjklunk at ucdavis.edu
 
Another weed in south Central Valley shows resistance to herbicide

Hairy fleabane, a common summer annual in the south Central Valley, has
joined the ranks of weeds that are resistant to
glyphosate, an herbicide sold under the brand name Roundup. This is the
first occurrence of glyphosate-resistant hairy
fleabane in the United States. 

Researchers suspect that this resistant weed may be widespread on
Central Valley roadsides and in orchards and vineyards.
Glyphosate-resistant hairy fleabane has also been found in South Africa,
Spain, Brazil and Columbia. 

A few years ago, some populations of rigid ryegrass and horseweed were
confirmed as glyphosate-resistant in California.
Worldwide, 13 weed species are resistant to the herbicide. 

Hairy fleabane is a prolific producer of fluffy seeds that can easily be
spread by wind. Growers and land managers have
been having trouble controlling this species with labeled rates of
glyphosate, leading researchers to study this weed's
resistance.

The resistance was first reported in 2005 in Fresno to UC Statewide
Integrated Pest Management Weed Ecologist Anil
Shrestha. Since then, Shrestha, USDA-ARS Scientist Brad Hanson, UC
Cooperative Extension Farm Advisor Kurt
Hembree, and student assistants Thomas Wang and Ivan Ramirez collected
seeds of hairy fleabane from several locations in
the Central Valley and tested them for resistance to glyphosate.

"After several tests, we found that the plants grown from seeds
collected from a roadside in Reedley, Calif., were more
resistant to glyphosate compared to the plants grown from seeds
collected from west Fresno and Davis," says Shrestha.

"We sprayed the herbicide at various growth stages of the plant ranging
from 8 to 11 leaves and 18 to 23 leaves. While most
of the plants collected from Davis and Fresno died with the labeled rate
of glyphosate, all the plants from Reedley showed
resistance to glyphosate. They generally survived after applications of
up to eight times the labeled rate. A few plants from Reedley even
survived a dose of 16 times the labeled rate of glyphosate.

"Glyphosate is an herbicide that provides broad-spectrum weed control,"
says Shrestha. "Appropriate strategies to prevent
herbicide-resistance must be taken to avoid losing this effective
herbicide." 

Herbicide-resistant plants evolve when the same herbicide with the same
overall manner of affecting a plant is used on them
repeatedly. Several articles have been published on this subject. An ANR
article on this topic is available online at:
http://anrcatalog.ucdavis.edu/pdf/8012.pdf. For more information about
hairy fleabane, visit http://www.ipm.ucdavis.edu. 

                                          #

Media contact: Anil Shrestha, IPM Weed Ecologist, (559) 646-6534,
anil at uckac.edu