Julius-Kühn-Archiv (Mar 2012)
Status and development of ACCase and ALS inhibitor resistant black-grass (Alopecurus myosuroides Huds.) in neighboring fields in Germany
Abstract
Neighboring fields in three local areas of southern Germany have been investigated for the infestation level and herbicide resistance structure of black-grass (Alopecurus myosuroides Huds.). One field within a local area, each with confirmed resistance, served as starting point to survey the surrounding fields. Eighty percent of the fields had very few black-grass ears prior to harvest, with mainly ears from single plants spread over the field. Infestation in the other fields was in large patches or widespread, yet in most situations it did not significantly impact on yield level. Resistance to ACCase-inhibiting herbicides was found on all tested fields in each region. Plants with a target-site mutation to ACCase inhibitors were found in all samples; in addition, most plants also exhibited non-target-site resistance. All five mutations conferring ACCase resistance were found. The diversity of the mutations between areas suggests that resistance evolved independently in most fields. At two locations, each one with confirmed ALS resistance, additional fields with reduced ALS efficacy were detected. At one location only the mutation P197T was found, at the second the W574L mutation was also found. Target-site resistance appears to be the major mechanism for these early cases of ALS inhibitor resistance. Understanding the resistance development in individual fields and the spatial dynamics requires investigation over several years. The example of ACCase resistance to black-grass demonstrates how a specific mode of action can be rendered ineffective over a whole region. It provides a possible model for ALS-inhibiting herbicides. In the current situation, farmers are able to manage the black-grass infestation quite well. Resistance in a field seems to develop first in patches with high population densities. Resistance management should therefore focus on the management of the seed bank of each field, using all measures to keep the population pressure low.
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