International survey of herbicide-resistant weeds: lessons and limitations

The "International Survey of Herbicide-Resistant Weeds" monitors the occurr ence of herbicide-resistant weeds throughout the world. Currently there are 222 herbicide resistant weed biotypes (147 unique species) found in 45 cou ntries. Whilst triazine-resistant weeds account for 61 of these cases, ALS inhibitor and ACCase inhibitor-resistant weed species are now of greater ec onomic importance globally. There are 58 ALS inhibitor-resistant weed speci es found in 14 countries and 19 species of ACCase inhibitor-resistant grass es found in 17 countries. ALS inhibitor-resistant weeds are most problemati c in cereal, corn/soybean, and rice production. ACCase inhibitor resistant Lolium and Avena spp. threaten cereal production in Australia, Canada, Chil e, France, Saudi Arabia, South Africa, Spain, the United Kingdom, and the U SA. Grasses now comprise 40% of all resistant weed biotypes indicating that this family has the greatest propensity to evolve resistance to herbicides . The incidence of resistance is rapidly increasing in Asia and South Ameri ca as these regions adopt high input agriculture. Researchers from 60 count ries have assisted in completing 583 survey forms to report herbicide-resis tant weeds, either via regular mail or over the Internet. The survey is not without its limitations. Estimating the number of resistant sites and the area infested is extremely difficult and is likely to be inaccurate in many cases. Occasionally incorrect identification of species or inappropriate t esting procedures has led to retraction of records from the survey database . The survey is brief to encourage participation, and detailed information about the genetics, mechanisms, or even cross-resistances are sought from f ollow-up questions or the scientific literature and posted along with the s urvey results at http://www.weedscience.com.