Influence of Adjuvants on the Efficacy of Tolpyralate plus Atrazine for the Control of Annual Grass and Broadleaf Weeds in Corn with and without Roundup WeatherMAX<sup>®</sup>

Abstract

Tolpyralate is a new HPPD-inhibiting herbicide that is efficacious on annual grass and broadleaf weed species in corn. For maximum herbicide performance of tolpyralate, it is recommended that atrazine is tank mixed with tolpyralate along with the adjuvants methylated seed oil concentrate (MSO) plus urea ammonia nitrate (UAN). A common use pattern of tolpyralate plus atrazine will be in a tank mix with Roundup WeatherMAX® due to the high proportion of corn acres that are seeded to Roundup Ready® hybrids in Eastern Canada. There is no information in the peer-reviewed literature if the adjuvant system in Roundup WeatherMAX® is adequate for optimal herbicide performance of tolpyralate plus atrazine, or if MSO and UAN are still required. Six field trials were conducted over two years near Ridgetown and Exeter, ON, Canada to determine if adjuvants are still required when tolpyralate plus atrazine is tank mixed with Roundup WeatherMAX® in corn. Tolpyralate plus atrazine plus MSO and Roundup WeatherMAX® plus tolpyralate plus atrazine provided excellent control of velvetleaf, pigweed spp, common ragweed, lambsquarters, ladysthumb, wild mustard, flower-of-an-hour, barnyardgrass and green foxtail in this study. Results of this study show that in the absence of Roundup WeatherMAX®, weed control with tolpyralate plus atrazine was improved substantially with the addition of MSO; however, there was little to no increase in weed control with the addition of UAN. When tolpyralate plus atrazine was co-applied with Roundup WeatherMAX®, there was no improvement in weed control with the addition of MSO and/or UAN.

Enhancement of Tolpyralate + Bromoxynil Efficacy With Adjuvants in Corn

“…In the current study, velvetleaf control was 89-100% at 2, 4, and 8 WAA when tolpyralate + bromoxynil was applied with and without the addition of adjuvants. This is comparable to previous studies that reported velvetleaf control of 86-99% with tolpyralate + MSO Concentrate®, tolpyralate + atrazine + MSO Concentrate®, tolpyralate + atrazine + glyphosate, and tolpyralate + atrazine + glyphosate + MSO Concentrate® (Langdon et al, 2020;Metzger et al, 2018). In agreement with the control data, the density and dry biomass reduction of velvetleaf with tolpyralate + bromoxynil was similar among the different adjuvant treatments.…”

“…Similarly, Harbour et al (2003) found that four different surfactants did not improve kochia or Russian thistle control with bromoxynil. In contrast, Langdon et al (2020) reported that velvetleaf control with tolpyralate + atrazine was enhanced with the addition of MSO Concentrate®; however, when glyphosate was co-applied with tolpyralate + atrazine, MSO Concentrate® did not improve velvetleaf control. Previous research has reported >90% velvetleaf control with bromoxynil applied without the addition of an adjuvant, which may have contributed to the inability to detect a benefit of adjuvant addition to tolpyralate + bromoxynil (Corbett et al, 2004).…”

“…Activator adjuvants such as oil adjuvants and surfactants can improve the efficacy of foliar-applied herbicides (Harbour et al, 2003;Langdon et al, 2020). The most effective adjuvant to add to a herbicide depends on the herbicide and target weed species.…”

“…Beauv.] was enhanced when MSO Concentrate® was added to tolpyralate + atrazine (Langdon et al, 2020). In contrast, control of common ragweed and wild mustard was not improved at 8 weeks after application (WAA) with the addition of MSO Concentrate® (Langdon et al, 2020).…”

“…was enhanced when MSO Concentrate® was added to tolpyralate + atrazine (Langdon et al, 2020). In contrast, control of common ragweed and wild mustard was not improved at 8 weeks after application (WAA) with the addition of MSO Concentrate® (Langdon et al, 2020). Langdon et al (2020) also reported that the addition of MSO Concentrate® did not improve weed control when tolpyralate + atrazine was co-applied with glyphosate.…”