Effect of Glyphosate on Guineagrass Submitted to Different Soil Water Potential

ABSTRACT: The action of herbicides on weeds that develop under water deficit can be compromised, because the routes of penetration of hydrophilic herbicides are reduced due to the lower hydration of the cuticle in these plants. Moreover, hydrophobic compounds found in the epicuticular wax coating of plants under water stress, hinder the penetration of hydrophilic compounds. This study evaluated the control efficiency of glyphosate on guineagrass plants when submitted to different water deficits. The study was conducted in a greenhouse, and treatments were composed of guineagrass plants submitted to three soil water conditions [low water deficit (13%), intermediate water deficit (10%) and high water restriction (8%)], three doses of glyphosate (0.0, 270.0 and 540.0 g ha-1) and two phenological stages of plant development (4-6 leaves and 1-3 tillers). The water management started when plants presented two developed leaves. Visual evaluations were performed 7, 14, 21 and 35 days after the application of the herbicide; the morpho-physiological parameters of the specific leaf area, stomatal conductance and the difference between the environment temperature and the leaf temperature on the day of the herbicide application were also analyzed at the end of the study, as well as the dry matter of shoot and root. With the increase of the water restriction, there was a decrease in the analyzed morpho-physiological parameters, as well as in the dry matter accumulation of the shoot and roots of the studied plants. Plant control was more efficient when a 540 g ha-1 dose of glyphosate was applied, and when they were controlled at their vegetative stage of 1-3 tiller, and with a water management of 13%. It is possible to state that guineagrass under water restriction have less control efficacy when treated with glyphosate.

摘要：除草剂对缺水环境下生长杂草的防控效果可能会受到削弱，原因在于亲水型除草剂的渗透途径会因这类植物表皮（cuticle）的水合度降低而减少。此外，水分胁迫下植物表皮蜡质层（epicuticular wax coating）中存在的疏水化合物，会阻碍亲水型化合物的渗透。本研究针对不同缺水条件下草甘膦（glyphosate）对几内亚草（guineagrass）的防除效果展开了评估。本试验于温室环境中开展，试验处理包含三类：经受3种土壤水分条件[低缺水（13%）、中缺水（10%）和高水分限制（8%）]的几内亚草植株、3个草甘膦施用量梯度（0.0、270.0和540.0 g·ha⁻¹）以及2个植物发育物候期（4~6叶期和1~3分蘖期）。水分调控处理始于植株长出2片完全展开叶之时。分别于除草剂施用后第7、14、21和35天开展目视评估；试验结束时，还测定了比叶面积（specific leaf area）、气孔导度（stomatal conductance）、施药当日环境温度与叶温差值等形态生理参数，以及地上部与根系干物质含量。随着水分限制程度加剧，供试植株的各项形态生理参数、地上部与根系干物质积累量均显著降低。当草甘膦施用量为540.0 g·ha⁻¹、植株处于1~3分蘖的营养生长期，且水分调控水平为13%时，几内亚草的防除效果最佳。综上可得出结论：经受水分限制的几内亚草经草甘膦处理后，其防除效果会有所下降。