Julius-Kühn-Archiv (Mar 2012)
Amaranthus develops resistance to HPPD inhibitors in seed corn production fields - another example of lack of diversity in the weed control program
Abstract
In 2010, a hybrid seed corn production field was confirmed to be infested with a population of Amaranthus tuberculatus that was not controlled by postemergence applications of all tested commercially available HPPDinhibitor herbicides. In glasshouse and field studies, resistance to post-emergence applications of mesotrione, tembotrione and topramezone was confirmed. In addition, this population was identified to be resistant to ALSinhibitors and to triazines. A. tuberculatus is a very competitive weed, which can appear in high population density and can emerge even very late during the season. A. tuberculatus is dioecious and therefore an obligate outcrosser, which is leading to high genetic variability within a population. All these biological features increase the risk of developing resistance to herbicides. Therefore, the field history explains clearly that this resistance developed under specific conditions. In this field, inbred corn was grown for at least seven consecutive years. Inbred corn is much less competitive with weeds compared to hybrid field corn and herbicide options are reduced vs. hybrid field corn production. In addition due to the resistance to triazines, only one effective mode of action (HPPD) has been used post-emergence to control A. tuberculatus for over seven consecutive years. The resistance development in this A. tuberculatus population is clearly a result of the lack of diversity in the weed management plan which should include crop and herbicide rotation. Field testing showed pre-emergence applications of mesotrione combinations (Lumax®, Lexar®) provided good control of this A. tuberculatus population. In addition alternative herbicides to control this population have been identified: Glyphosate, glufosinate, paraquat, PPGO-inhibitors, auxins, and triazinones were very effective.
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