Greg R. Kruger
Date of this Version
B. C. Vieira, Herbicide Drift Influence on Amaranthus spp. Herbicide Resistance Evolution. PhD diss., Department of Agronomy & Horticulture, University of Nebraska–Lincoln, 2019.
The adverse consequences of herbicide drift towards sensitive crops have been extensively reported in the literature. However, no information is available on the consequences of herbicide drift onto weed species inhabiting boundaries of agricultural fields. Exposure to herbicide drift could be detrimental to long-term weed management as several weed species have evolved herbicide resistance after recurrent selection with low herbicide rates. Despite the herbicide drift exposure and its potential implications on resistance evolution and weed management, resistance prone weed species such as Palmer amaranth (Amaranthus palmeri) and waterhemp (Amaranthus tuberculatus) are often neglected and not properly managed in agricultural field margins.
The first study of this research investigated the frequency and distribution of glyphosate-resistant Amaranthus spp. in Nebraska. The study also investigated how agronomic practices influenced the occurrence of glyphosate resistance in Amaranthus spp. in Nebraska. While glyphosate resistance was widespread in waterhemp, few glyphosate-resistant Palmer amaranth populations were reported in Nebraska. Weed species, geographic region within the state, and current crop were the most important factors predicting the occurrence of glyphosate resistance in fields infested with Amaranthus spp. in Nebraska. Moreover, glyphosate resistance was widespread in waterhemp populations collected on field borders and ditches.
The second study investigated the near-field deposition of glyphosate, 2,4-D, and dicamba spray drift from applications with two different nozzles in a low-speed wind tunnel, and their impact on Palmer amaranth and waterhemp growth and development. Herbicide drift was influenced by nozzle design and resulted in Amaranthus spp. biomass reduction or complete plant mortality. Herbicide drift can expose weeds inhabiting field margins to herbicide rates previously reported to select for herbicide-resistant biotypes.
The third study investigated if recurrent selection with glyphosate, 2,4-D, and dicamba spray drift could select for Amaranthus spp. biotypes with reduced herbicide-susceptibility over two generations. The study results confirmed that herbicide drift towards field margins can rapidly select for weed biotypes with reduced herbicide sensitivity. Preventing the establishment of resistance prone weeds on field margins is an important management strategy to delay herbicide resistance. Weed management programs should consider strategies to mitigate near-field spray drift, and suppress weed populations on field borders.
Advisor: Greg R. Kruger