The influence of manganese on glyphosate efficacy in ryegrass (Lolium spp.)

[摘要] ENGLISH ABSTRACT: In the Western Cape of South Africa, ryegrass (Lolium spp.) developed resistance to the herbicide glyphosate within wheat fields, orchards and vineyards. The influence that plant available Mn might have on glyphosate resistance in ryegrass were investigated by measuring percentage survival and dry matter production in response to Mn treatments and glyphosate dosage rates.Four different trials were conducted in this study. In the first trial, glyphosate dosage response was tested against the effect of added Mn treatment levels on glyphosate susceptible and resistant ryegrass populations. In the second trial, glyphosate dosage response was tested against the effect of soil types of differing Mn contents. In the third trial, glyphosate dosage response was tested against ryegrass species found in agricultural setting in soils of different Mn content from the same farm where it naturally grew. Glyphosate dosage response in ryegrass were lastly also tested under varying temperature ranges and Mn treatment levels.Glyphosate efficacy was found to exhibit trends of decline at higher Mn treatment levels, especially at sublethal dosage rates or soils of naturally higher Mn content. Ryegrass originating from a soil of higher Mn content (biotype R3) as opposed to their counterparts seemed to be naturally more inclined to a magnified resistance, regardless of the soil into which it was transplanted.When testing glyphosate dosage response against Mn treatment level and temperature conditions, trends showed that regardless of the temperature conditions ryegrass were subjected to, Mn levels played a distinct role in glyphosate efficacy. Added Mn exhibited trends of better survival rates than control treatments throughout the temperature conditions. At 25-30°C, glyphosate efficacy was reduced compared to the lower temperature ranges.Generally, it was found that Mn treatments seemed to exert some effect of decreased glyphosate efficacy in ryegrass albeit only at low, sub-lethal dosage rates. Trends indicated that some levels of added plant available Mn seemed to curb glyphosate efficacy at low dosage rates. It was concluded that some effect must exist where plant available Mn influences the herbicidal activity of glyphosate in a negative manner. Reduced translocation is the most likely explanation for this trend. This reduced efficacy probably occurs as a result of either complexation of glyphosate with Mn and subsequent reduced uptake or vacuolar sequestration. However, Mn did not affect glyphosate efficacy at recommended dosage rates. Results of this study emphasize the importance of applying glyphosate at recommended dosage rates and never to apply below recommended dosage rates.

[发布机构] Stellenbosch University