Distribution, biology, and management of glyphosate-resistant horseweed in no-till crop production.

摘要

Current no-till production practices are heavily reliant on postemergence glyphosate for weed control facilitated by >90% adoption of glyphosate-resistant (GR) soybean. Horseweed, Conyza canadensis, is an increasingly common and problematic annual broadleaf weed due to the frequent occurrence of glyphosate-resistant biotypes. GR horseweed has currently been documented in over 1/3 of the states in the continental U.S infesting greater than two million hectares. Six research experiments were conducted. The objectives were: determine the presence of GR horseweed in Indiana soybean fields, determine the potential to predict glyphosate resistance in horseweed populations using in-field survey data, characterize levels of glyphosate resistance in horseweed populations and selected biotypes, characterize growth and seed production of biotypes with single and multiple resistance to glyphosate and acetolactate synthase (ALS) inhibiting herbicides, determine the influence of various management practices on GR population densities in a long-term no-till field experiment, and evaluate horseweed control from residual preplant herbicides. To begin there were 850 Indiana soybean fields sampled, 158 horseweed populations collected, and 88 determined resistant to glyphosate. The GR populations were found in all regions but were most frequent (38%) in the southeastern region of Indiana. Glyphosate response (resistant or susceptible) for each population was predicted using several 'real-time' in-field data factors. GR and glyphosate-susceptible (GS) populations were predicted with 89 and 51% accuracy by field surveyors, respectively. Among the GR populations collected, resistance fluctuated 22-fold from low- to high-levels of resistance. However, differences diminished to 2-fold in first-generation progeny after plants selected to represent the continuum of low- to high-level resistance were self pollinated. Three field experiments were conducted in southeastern Indiana. In the first, there were no differences in the growth or seed production between glyphosate-, ALS-, and glyphosate+ALS inhibitor-resistant populations. In a long-term no-till experiment, spring preplant applications consistently reduced horseweed densities more than fall applications, residual herbicides reduced densities more than glyphosate applied alone, and corn-soybean rotation reduced densities more than continuous soybean. Management systems also shifted the ratio of GR:GS biotypes from an initial ratio of 3:1 to 1:6 after four years of residual preplant herbicide use followed by non-glyphosate postemergence herbicides.