Abstract

The most effective adjuvant is often herbicide-specific and dependent on the target weed species. Tolpyralate is a 4-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide that is usually tank-mixed with atrazine for improved weed control in corn (Zea mays L.). Previous research has reported that a methylated seed oil (MSO) adjuvant (MSO Concentrate®) enhances the efficacy of tolpyralate + atrazine on several annual broadleaf and grass weed species. The efficacy of tolpyralate can also be improved with the addition of bromoxynil instead of atrazine; however, there is no information in the peer-reviewed literature that tests the efficacy of tolpyralate + bromoxynil with different adjuvants. Therefore, four field trials were conducted in 2020 and 2021 in Ontario, Canada to evaluate the efficacy of tolpyralate + bromoxynil without an added adjuvant and with MSO Concentrate®, Agral® 90, Assist® Oil Concentrate, Carrier®, LI 700®, or Merge® on six annual weed species in corn. The adjuvants did not enhance control of wild mustard (Sinapis arvensis L.) or velvetleaf (Abutilon theophrasti Medik.) with tolpyralate + bromoxynil. At 8 weeks after application (WAA), common ragweed (Ambrosia artemisiifolia L.) control was improved with the addition of MSO Concentrate® or Merge® to tolpyralate + bromoxynil. At 8 WAA, all adjuvants enhanced the control of common lambsquarters (Chenopodium album L.) with tolpyralate + bromoxynil similarly except for Assist® Oil Concentrate; Merge® was a better adjuvant than Assist® Oil Concentrate for common lambsquarters control. At 8 WAA, control of barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] was enhanced with the addition of Assist® Oil Concentrate, Carrier®, MSO Concentrate®, or Merge® to tolpyralate + bromoxynil. Carrier®, MSO Concentrate®, and Merge® enhanced the efficacy of tolpyralate + bromoxynil on Setaria spp. at 8 WAA. Control of velvetleaf, wild mustard, common ragweed, Setaria spp., and barnyardgrass with tolpyralate + bromoxynil was similar with the six adjuvants evaluated at 8 WAA.

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