Monsanto has confirmed that a Johnsongrass biotype has become resistant to glyphosate in Northeastern Argentina.

The findings were announced last week by companies represented by two of the major fertilizer and agrochemical trade organizations in Argentina and Monsanto.

No Johnsongrass resistance has been identified in the United States.

Monsanto took the initiative in researching reports in 2004 of resistance and has worked with the industry to develop recommendations to mitigate the resistance.

A preliminary assessment of the affected area identified the problem on 17,000 to 25,000 acres.

Monsanto and the agricultural organizations have developed recommendations to mitigate the documented resistance.

Several weed species have been identified as resistant to glyphosate in the U.S. and Monsanto has developed agressive vegetaion management plans to mitigate those situation as well. Among them is an online weed resistance management continuing education course for California and Arizona pest control advisors on the Western Farm Press website. Monsanto also sponsors a major online resistance course for Midwest and Southern corn producers.

Information in these courses includes recommendation for chemical control with herbicides other than glyphosate as well as recommendations for mechanical and non-chemical control.