Effect of Adjuvant on Glyphosate Effectiveness, Retention, Absorption and Translocation in Lolium rigidum and Conyza canadensis.

Candelario Palma-Bautista,Jose G Vazquez-Garcia,José A Domínguez-Valenzuela,Rafael De Prado,Alexandros Tataridas,Ilias Travlos,Panagiotis Kanatas

doi:10.3390/plants9030297

Candelario Palma-Bautista, Jose G Vazquez-Garcia + Show 5 more

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https://doi.org/10.3390/plants9030297

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Abstract

Glyphosate retention, absorption and translocation with and without adjuvant were examined in Lolium rigidum and Conyza canadensis in greenhouse and laboratory settings to develop an understanding of the influence of the selected adjuvant on glyphosate activity. Tests on whole plants show that the dose of herbicide needed to reduce dry weight by 50% (GR50) or plant survival (LD50) decreases by mixing glyphosate and adjuvant to 22%–24% and 42%–44% for both populations of L. rigidum and C. canadensis, respectively. This improvement in efficacy could be attributed to the higher herbicide retention and lower contact angle of the glyphosate + adjuvant drops on the leaf surface compared to the glyphosate solution alone. Plants of both species treated with 14C-glyphosate + adjuvant absorbed more glyphosate compared to non-adjuvant addition. Furthermore, the movement of the herbicide through the plant was faster and greater with the adjuvant. Our results reveal that the use of adjuvants improves the effectiveness of glyphosate in two of the most important weeds in agricultural crops in Mediterranean countries.

Highlights

Glyphosate [N-(phosphonomethyl) glycine] has been used worldwide for several decades in a wide range of agricultural and non-agricultural situations, with glyphosate-based herbicides serving as broad-spectrum, water-soluble, non-selective, systemic, post-emergence herbicides [1,2,3,4]
C. canadensis and L. rigidum exhibited a high sensitivity to glyphosate at the rosette and 3–4 leaf growth stage, respectively, showing very low LD50 values compared to 1080 g ae ha−1 —the field dose generally used by farmers in agricultural crops (Table 1 and Figure 1B,D)
Our results indicate that 96 h after treatment (HAT) glyphosate uptake is increased—a result that is similar to Fernandez Moreno et al [13], who tested the uptake and translocation of glyphosate in a susceptible and a resistant population of rigid ryegrass in Spain

Summary

Introduction

Glyphosate [N-(phosphonomethyl) glycine] has been used worldwide for several decades in a wide range of agricultural and non-agricultural situations, with glyphosate-based herbicides serving as broad-spectrum, water-soluble, non-selective, systemic, post-emergence herbicides [1,2,3,4]. Its mode of action is the inhibition of the shikimic acid pathway, blocking the synthesis of the aromatic amino acids (AAA) phenylalanine (Phe), tryptophan (Trp), and tyrosine (Tyr) [2,3]. Glyphosate is considered as the most important herbicide globally [2], which has led to overreliance on it. There are more than five hundred cases worldwide of weeds which have evolved herbicide resistance [5]. A proactive approach to preventing GR weeds could be achieved by including alternative herbicides with different mechanisms of action, by improving herbicide efficacy and through the Plants 2020, 9, 297; doi:10.3390/plants9030297 www.mdpi.com/journal/plants

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