This research was conducted with glyphosate resistant biotypes of tropical S halepense and temperate L rigidum in which we had established that the reduced glyphosate translocation resistance mechanism is present. These biotypes do not appear to have any target site EPSPS gene mutations.
Good work from the Sammons laboratory at Monsanto has demonstrated with glyphosate resistant Conyza biotypes with the reduced glyphosate translocation resistance mechanism (increased vacuolar sequestration) that the level of glyphosate resistance is considerably lower at low temperatures.
Here we examined the temperature dependence of glyphosate resistance in tropical warm season S halepense versus temperate cool season L rigidum biotypes with the reduced glyphosate translocation resistance mechanism. With these contrasting warm season versus cool season species the results are very clear that glyphosate resistance level is temperature dependent in that the reduced glyphosate translocation resistance mechanism is inefficient at low temperatures. This is good confirmation of the results of Sammons et al and extends the observations to the warm season S halepense. Indeed, in some cases, it may be possible to achieve control of glyphosate resistant biotypes with this reduced translocation resistance mechanism if plants can be treated at times of low temperature.