Abstract

Halauxifen-methyl is a new synthetic auxin herbicide for broadleaf weed control prior to planting of corn, cotton, and soybean. Experiments were conducted to evaluate the efficacy of herbicide programs containing halauxifen-methyl for control of glyphosate-resistant (GR) horseweed and other problematic weed species in comparison to existing herbicides programs utilized in no-till GR soybean systems. Halauxifen-methyl-, dicamba-, and saflufenacil-based herbicide programs controlled GR horseweed, while glufosinate and 2,4-D herbicide programs resulted in lower GR horseweed control. The addition of ALS and PPO inhibitor herbicides with soil residual activity increased GR horseweed control of herbicide programs with halauxifen-methyl and glufosinate.

Halauxifen-methyl applied alone or in tank-mixtures controlled both GR horseweed and common ragweed. However, the addition of either 2,4-D or dicamba was necessary to increase the weed control spectrum of halauxifen-methyl in preplant burndown applications.

Synthetic auxin herbicides such as 2,4-D and dicamba have preplant interval restrictions for soybean. Research was conducted to evaluate the potential of halauxifen-methyl to cause soybean phytotoxicity when applied at five different preplant intervals. Soybean phytotoxicity from halauxifen-methyl applied at any preplant interval did not occur in 2015. Soybean phytotoxicity ranging from 1 to 15% was observed in 2016 at 14 days after planting for applications made at 14, 7, and 0 days before planting. However, soybean plants quickly recovered and phytotoxicity was negligible at 21 days after planting.

Research was conducted to evaluate the efficacy of halauxifen-methyl and dicamba alone and in tank-mixtures with 2,4-D, glyphosate, and chlorimuron + tribenuron for control of fall-emerged GR horseweed. Fall applications of halauxifen-methyl, 2,4-D, and dicamba control fall-emerged horseweed and reduce GR horseweed height in the spring. However, control of winter annual weeds can increase spring horseweed emergence.

Halauxifen-methyl controls GR horseweed and common ragweed in spring preplant burndown applications and fall-emerged horseweed in fall burndown applications; however, tank-mixtures are required to increase the weed control spectrum of the herbicide. Halauxifen-methyl can cause minor phytotoxicity to soybean unifoliates, although it did not impact soybean stands or grain yield. The potential use of halauxifen-methyl for weed management in preplant burndown applications will depend on market price, adoption of dicamba- and 2,4-D-tolerant crops, and the spectrum of weeds present at burndown.

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Botany and Plant Pathology

Committee Chair

William G. Johnson

Date of Award

12-2017

Committee Member 1

Bryan G. Young

Committee Member 2

Shaun N. Casteel

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