Abstract
Tolpyralate is a new benzoylpyrazole herbicide for weed management in corn. It is recommended to be co-applied with atrazine along with the adjuvants methylated seed oil concentrate (MSO) plus an ammonium nitrogen fertilizer, such as urea ammonium nitrate (UAN). Two studies were conducted on glyphosate-resistant (GR) Canada fleabane and GR waterhemp to determine if an additional adjuvant is still required when tolpyralate plus atrazine are tankmixed with a commercial glyphosate formulation (Roundup WeatherMAX®) in corn. Trials were conducted over a two-year period (2018-19) on farms in south western Ontario with confirmed GR populations. When co-applied with Roundup WeatherMAX®, the addition of MSO to tolpyralate + atrazine increased control of GR waterhemp 9%; however, there was no increase in GR Canada fleabane control from the addition of additional adjuvants. At 8 WAA, all treatments provided > 91% and > 84% control of GR waterhemp and GR Canada fleabane, respectively. This study concludes that the addition of Roundup WeatherMAX® to tolpyralate plus atrazine improves the control of GR waterhemp and GR Canada fleabane in corn.
Highlights
Glyphosate-resistant (GR) waterhemp (Amaranthus tuberculatus) and GR Canada fleabane
Data analysis indicated that the Roundup Weather MAX® by tolpyralate + atrazine interaction was not significant for GR waterhemp density (P = 0.6348) and biomass (P = 0.9906) and corn yield (P = 0.3225) (Table 3)
Averaged across the 0 and 900 g∙ae∙ha−1 of Roundup WeatherMAX®, tolpyralate + atrazine reduced GR waterhemp density and biomass, the decrease in density and biomass were greater with the addition of methylated seed oil concentrate (MSO) or MSO + urea ammonium nitrate (UAN) compared to UAN
Summary
Glyphosate-resistant (GR) waterhemp (Amaranthus tuberculatus) and GR Canada fleabane Competitive, troublesome weed with an extended emergence from early spring until October [1]. Waterhemp requires cross pollination, resulting in genetic and phenotypic variability, accelerated spread of resistance genes, and the ability to adapt to diverse environmental conditions [6]. The first GR waterhemp population in Ontario was confirmed from seed collected in 2014 in Lambton county [1]. Waterhemp biotypes in Ontario have confirmed resistance to Groups 2, 5, 9, and 14 herbicides [7]. Of the waterhemp populations in Ontario, it was estimated that 61% have 3-way multiple resistance to imazethapyr, atrazine and glyphosate [1]. Wats); it is more competitive and causes greater yield reductions than redroot pigweed (A. retroflexus L.) [11]
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