Interaction of the Bioherbicide &amp;lt;i&amp;gt;Myrothecium verrucaria&amp;lt;/i&amp;gt; with Technical-Grade Glyphosate on Glyphosate-Susceptible and -Resistant Palmer Amaranth

Robert E Hoagland,Robin H Jordan,Kenneth C Stetina,C Douglas Boyette

doi:10.4236/ajps.2018.911167

Abstract

Previously we found that a strain of Myrothecium verrucaria (MV) exhibited bioherbicidal activity against several important weeds, and that some commercial formulations of glyphosate applied with MV resulted in synergistic interactions that improved weed control efficacy. We also found that MV had bioherbicidal activity against glyphosate-resistant Palmer amaranth. We have also reported that some commercial formulations are inhibitory to MV. Our objectives were to test the effect of unformulated glyphosate (high purity, technical-grade glyphosate) alone and in combination with MV for bioherbicidal activity on glyphosate-susceptible and -resistant Palmer amaranth biotypes under greenhouse conditions and to examine technical-grade glyphosate on the growth of this bioherbicide. High purity glyphosate (without adjuvants/surfactants) was not toxic to MV growth and sporulation at concentrations up to 2.0 mM when grown on agar supplemented with the herbicide. Both biotypes were injured by MV and MV plus glyphosate treatments as early as 19 h after application (3 h after a dew period of 16 h). These injury effects increased and were more evident through the 6-day time course, when after 120 h the MV plus glyphosate treatment had killed all glyphosate-susceptible and -resistant plants. The interaction of glyphosate plus MV was synergistic toward the control of Palmer amaranth. Data strongly suggest that the active ingredient is responsible for the synergy previously found when this bioherbicide was combined with some commercial formulations of glyphosate. Results demonstrated that MV can control both glyphosate-resistant and -susceptible Palmer amaranth seedlings and act synergistically with high-purity glyphosate to provide improved weed control.

Highlights

IntroductionOriginally controlled with the herbicide glyphosate, Palmer amaranth has become resistant to glyphosate, and resistant biotypes are widely distributed [3]
We found that a strain of Myrothecium verrucaria (MV) exhibited bioherbicidal activity against several important weeds, and that some commercial formulations of glyphosate applied with MV resulted in synergistic interactions that improved weed control efficacy
We found that MV had bioherbicidal activity against glyphosate-resistant Palmer amaranth

Summary

Introduction

Originally controlled with the herbicide glyphosate, Palmer amaranth has become resistant to glyphosate, and resistant biotypes are widely distributed [3] This weed is an abundant seed producer, for example up to 400,000 per plant [11] and herbicide resistance traits can be transferred when Palmer amaranth cross-breeds with the related weed, water hemp (Amaranthus rudis) [12]. Glyphosate resistance in Palmer amaranth plants is due to high copy numbers of the EPSPS gene, relative to that in glyphosate-susceptible plants [16] This high EPSPS copy number enables the plant to produce adequate EPSPS to support required aromatic amino acid production even when high levels of glyphosate are present in plant tissues. The transfer of resistance through cross-breeding, its aggressive nature and the prolific seed producing capacity of this weed [12] exacerbate its spread

Objectives

Methods

Results