TITLE:
Interaction of the Bioherbicide Myrothecium verrucaria with Technical-Grade Glyphosate on Glyphosate-Susceptible and -Resistant Palmer Amaranth
AUTHORS:
Robert E. Hoagland, C. Douglas Boyette, Robin H. Jordan, Kenneth C. Stetina
KEYWORDS:
Amaranthus palmeri, Biocontrol Agent, Bioherbicide, Biological Weed Control, Glyphosate-Resistance, Myrothecium verrucaria, Palmer Amaranth, Pigweed
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.9 No.11,
October
29,
2018
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.