Management of Glyphosate-Resistant Weeds in Mexican Citrus Groves: Chemical Alternatives and Economic Viability

Abstract

Glyphosate is a cheap herbicide that has been used to control a wide range of weeds (4–6 times/year) in citrus groves of the Gulf of Mexico; however, its excessive use has selected for glyphosate-resistant weeds. We evaluated the efficacy and economic viability of 13 herbicide treatments (glyphosate combined with PRE- and/or POST-emergence herbicides and other alternative treatments), applied in tank-mixture or sequence, to control glyphosate-resistant weeds in two Persian lime groves (referred to as SM-I and SM-II) of the municipality of Acateno, Puebla, during two years (2014 and 2015). The SM-I and SM-II fields had 243 and 346 weeds/m2, respectively, composed mainly of Bidens pilosa and Leptochloa virgata. Echinochloa colona was also frequent in SM-II. The glyphosate alone treatments (1080, 1440, or 1800 g ae ha−1) presented control levels of the total weed population ranging from 64% to 85% at 15, 30, and 45 d after treatment (DAT) in both fields. Mixtures of glyphosate with grass herbicides such as fluazifop-p-butyl, sethoxydim, and clethodim efficiently controlled E. colona and L. virgata, but favored the regrowth of B. pilosa. The sequential applications of glyphosate + (bromacil + diuron) and glufosinate + oxyfluorfen controlled more than 85% the total weed community for more than 75 days. However, these treatments were between 360% and 390% more expensive (1.79 and 1.89 $/day ha−1 of satisfactory weed control, respectively), compared to the representative treatment (glyphosate 1080 g ae ha−1 = USD $29.0 ha−1). In practical and economic terms, glufosinate alone was the best treatment controlling glyphosate resistant weeds maintaining control levels >80% for at least 60 DAT ($1.35/day ha−1). The rest of the treatments, applied in tank-mix or in sequence with glyphosate, had similar or lower control levels (~70%) than glyphosate at 1080 g ae ha−1. The adoption of glufosiante alone, glufosinate + oxyfluorfen or glyphosate + (bromacil + diuron) must consider the cost of satisfactory weed control per day, the period of weed control, as well as other factors associated with production costs to obtain an integrated weed management in the short and long term.

Effect of Phosphinothricin on Transgenic Downy Birch (Betula pubescens Ehrh.) Containing bar or GS1 Genes

“…The absence of glufosinate-resistant weeds suggests a high specificity of the action of this herbicide and provides it with an advantage over the widely used glyphosate. It was shown that glufosinate from the practical and economic points of view turned out to be the best for the control of glyphosate-tolerant weeds in citrus orchards [58]. However, the study of the metabolome in several PPT-tolerant transgenic cultures demonstrated increased accumulation of acetylamino adipate and acetyl tryptophan, which indicated non-specific activity of the bar gene [59].…”

Glyphosate ban in Mexico: potential impacts on agriculture and weed management

“…The resistance mechanisms in the six glyphosate‐resistant weeds found in Mexico were determine by just one research team 99–104 . Knowing these mechanisms has provided a basis for the management of herbicide resistant weeds in citrus; 105,106 however, these efforts are insignificant considering the extensive area planted in Mexico, of which citrus crops occupied only 4.2% (641 900 ha) in 2019 9 . The resistance mechanisms of herbicide resistant weeds found in wheat were characterized, 107–109 but have not been determined in any resistant weeds found in maize.…”

Non-Target Site Mechanisms Endow Resistance to Glyphosate in Saltmarsh Aster (Aster squamatus)

“…This herbicide disrupts the biosynthesis of tryptophan, phenylalanine and tyrosine by interrupting the activity of the enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) [ 2 ]. Glyphosate is used to control all types of annual and perennial weeds [ 3 ], being the main weed control tool in citrus groves in Veracruz, Mexico [ 4 ].…”