Differential response of horseweed (Conyza canadensis) to halauxifen-methyl, 2,4-D, and dicamba

Abstract

Halauxifen-methyl is an auxin herbicide for broadleaf weed control in preplant applications to corn and soybean. Our objective for this research was to characterize the phytotoxicity of halauxifen-methyl on horseweed, relative to 2,4-D and dicamba, in terms of weed height, the response to an auxin synergist, and root activity. The 50% reduction in plant growth (GR50) value for halauxifen-methyl on rosette-sized plants was 0.05 g ae ha−1, 100 times less than the labeled use rate of 5 g ae ha−1, compared with 36 and 31 g ha−1 for 2,4-D and dicamba, respectively. In a whole-plant bioassay, 240 g ae ha−1 of 2,4-D was calculated as the GR50 value on horseweed 20-cm tall, whereas applications of only 53 and 0.40 g ae ha−1 were necessary for dicamba and halauxifen-methyl, respectively, to achieve the same response. As weed size decreased, there was a concomitant reduction in the estimated herbicide dose for the GR50 with similar differences observed between halauxifen-methyl and the other two auxin herbicides. The addition of diflufenzopyr, an auxin synergist, to 2,4-D and dicamba resulted in a synergistic response on horseweed. However, the addition of diflufenzopyr to halauxifen-methyl resulted in an additive or antagonistic effect, depending on rate of diflufenzopyr, demonstrating a distinctive physiological pathway for halauxifen-methyl compared with 2,4-D and dicamba. In the agar-based bioassays, GR50 values for horseweed root length for 2,4-D and dicamba were 0.16 and 0.19 µM, respectively, whereas only 0.004 µM halauxifen-methyl was required for a comparable root response. These results indicate that horseweed exhibits a high level of sensitivity to halauxifen-methyl and suggest the activity of halauxifen-methyl is different from that of 2,4-D and dicamba. These differences in herbicide activity may reflect differential absorption, translocation, metabolism, or targeting of auxin receptors found in horseweed.

Cotton tolerance to halauxifen-methyl applied preplant

“…In previous research, halauxifen controlled horseweed similarly to 2,4-D and dicamba (Ellis et al. 2017; McCauley and Young 2016; Zimmer et al. 2018a, 2018b).…”

“…(2018a, 2018b) observed 87% to 97% control of glyphosate-resistant horseweed from treatments containing halauxifen. In another study, halauxifen and dicamba controlled 30-cm-tall glyphosate-resistant horseweed 80%, whereas 2,4-D provided ≤50% control (McCauley and Young 2016).…”

Development of novel pesticides in the 21st century

“…106) It is effective in managing weed biotypes resistant to other modes of actin such as ALS-inhibitor herbicides, glyphosate, and triazine herbicides. It has been shown that the activity (sensitivity to horseweed) of halauxifen-methyl is different from that of 2,4-D and dicamba, 107) which are typical auxin-like herbicides.…”

Corteva Agriscience's perspective and commitment to managing herbicide resistance

“…Members of the arylpicolinate family demonstrate novel and differentiated characteristics in terms of use rate, spectrum, weed symptoms, environmental fate, toxicology profile, and molecular interaction as compared to other auxin chemotypes. 30,31 Florpyrauxifenbenzyl formulated products are recommended for broad spectrum weed control in rice production in Italy, where weed pressure is high, and weed resistance is a growing issue among farmers. Due to the special and challenging conditions for weed management in Italy, and after several years of development and characterization, Corteva designed a program, under which florpyrauxifen-benzyl products are recommended and only allowed to be used as part of pre-defined herbicide programs, which involve florpyrauxifen-benzyl formulated products (straight and pre-mixtures) and also other modes of action in pre-emergence and in post-emergence applications.…”

“…Florpyrauxifen‐benzyl (Rinskor active) and halauxifen methyl (Arylex™ active) are new herbicide active ingredients from Corteva Agriscience and are members of a unique synthetic auxin chemotype, the arylpicolinates (HRAC/WSSA Group 4). Members of the arylpicolinate family demonstrate novel and differentiated characteristics in terms of use rate, spectrum, weed symptoms, environmental fate, toxicology profile, and molecular interaction as compared to other auxin chemotypes 30,31 . Florpyrauxifen‐benzyl formulated products are recommended for broad spectrum weed control in rice production in Italy, where weed pressure is high, and weed resistance is a growing issue among farmers.…”