Is There a Benefit of Adding Atrazine to HPPD-Inhibiting Herbicides for Control of Multiple-Herbicide-Resistant, Including Group 5-Resistant, Waterhemp in Corn?

Darren E. Robinson,David C. Hooker,Nader Soltani,Lauren Benoit,Peter H. Sikkema,Amit J. Jhala,Christian Willemse

doi:10.5539/jas.v13n7p21

Abstract

The evolution of multiple-herbicide-resistant (MHR) waterhemp (resistant to Groups 2, 5, 9, and 14) in Ontario, Canada is challenging for growers. The complementary activity of the co-application of hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides with atrazine has been well documented. The objective of this research was to determine if the addition of atrazine to 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides applied postemergence improves their consistency of MHR waterhemp (including Group 5 resistance) in corn. Five field trials were conducted over a two-year period (2018, 2019) in Ontario, Canada. Five HPPD-inhibiting herbicides [isoxaflutole (105 g ha-1), mesotrione (100 g ha-1), topramezone (12.5 g ha-1), tembotrione (90 g ha-1), and tolpyralate (30 g ha-1)] were applied postemergence with and without atrazine to 10-cm-tall waterhemp. Corn injury (&le; 10%) was observed at specific sites where the application of tembotrione, isoxaflutole and isoxaflutole + atrazine resulted in characteristic white bleaching of corn foliage; however, yield was not affected. Averaged across field sites, the addition of atrazine to isoxaflutole, mesotrione, topramezone, or tembotrione improved MHR waterhemp control 15%, 11%, 7%, and 7%, respectively at 4 weeks after application (WAA). Averaged across herbicide treatments and sites, the addition of atrazine reduced the standard error of MHR waterhemp control by 13% to 100%. This study concludes that the co-application of atrazine with HPPD-inhibitors applied postemergence reduced the risk of herbicide failure and resulted in greater and more consistent control of MHR waterhemp.

Highlights

Waterhemp (Amaranthus tuberculatus) is ranked as one of the most troublesome weeds in corn production in the United States (Nordby & Hartzler, 2004)
Multiple-herbicide-resistant (MHR) waterhemp populations have since been identified in Ontario with four-way resistance to acetolactate synthase (ALS) (Group 2), photosystem II (PS II) (Group 5), 5-enolpyruyl shikimate-3-phosphate synthase (EPSPS) (Group 9) and protoporphyrinogen oxidase (PPO) (Group 14) inhibiting herbicides (Benoit et al, 2019a)
Control of MHR waterhemp with atrazine was variable within and across sites ranging from 28% to 96% while the standard error ranged from 1.4% to 10.3% 4, 8, and 12 weeks after application (WAA) (Table 3)

Summary

Introduction

Waterhemp (Amaranthus tuberculatus) is ranked as one of the most troublesome weeds in corn production in the United States (Nordby & Hartzler, 2004). The distribution of herbicide-resistant (HR) waterhemp currently includes 18 states in the United States and three Canadian provinces, including Ontario (Heap, 2020). Multiple-herbicide-resistant (MHR) waterhemp populations have since been identified in Ontario with four-way resistance to acetolactate synthase (ALS) (Group 2), photosystem II (PS II) (Group 5), 5-enolpyruyl shikimate-3-phosphate synthase (EPSPS) (Group 9) and protoporphyrinogen oxidase (PPO) (Group 14) inhibiting herbicides (Benoit et al, 2019a). A waterhemp population resistant to six herbicide modes-of-action (MOA) was reported in Missouri in 2015 with resistance to Group 2, synthetic auxins (Group 4), 5, 9, 14, and 4-hydroxyphenylpyruvate dioxygenase (HPPD) (Group 27) (Shergill et al, 2018). Waterhemp is the first weed species to evolve resistance to HPPD-inhibiting herbicides (Heap, 2020; McMullan & Green, 2011)

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Results