Water Deficit Effects on the Cotton Leaf Cuticle and the Efficiency of Defoliants

Abstract

Inconsistent results are often experienced with chemical defoliants in cotton (Gossypium hirsutum L.). Leaves of field‐and growth chamber‐grown plants were used in a 3‐yr study to evaluate the hypothesis that drought‐induced alterations in the leaf cuticle may be associated with the decreased efficiency of defoliants. Plants which experienced previous water stress had reduced defoliation and increased regrowth when treated with the commercial defoliant Harvade [dimethipim (2,3 dihydro‐5,6‐dimethyl‐1,4‐dithiin‐1,1,4,4‐tetraoxide) Uniroyal Chemical Co., Middlebury, CT]. Water deficit increased leaf cuticle thickness by 33%, altered the epicuticular wax composition, and increased total wax content. Chloroform extracts of the leaf cuticle indicated that water‐stressed leaves had increased concentrations of higher molecular weight waxes which increased the hydrophobicity of the leaf surface. Although the 14C‐labelled defoliant Harvade penetrated the leaf under both water regimes, 34% less defoliant entered the previously stressed leaves. The thicker, more hydrophobic cuticles of water‐stressed leaves decreased the penetration of the 14C‐labelled defoliant and this was reflected in the decreased defoliation efficiency. These results suggest that seasonal inconsistencies in defoliant efficiency may be related to the irrigation history of the crop. In cotton growing areas receiving inadequate rainfall or irrigation, defoliant rates may need to be increased or the choice of spray adjuvant changed.

Environmental Effects on Velvetleaf (Abutilon theophrasti) Epicuticular Wax Deposition and Herbicide Absorption

“…The results of this study reinforce the results by Retzlaff (1983), but also suggest that the quantity of ECW may affect bentazon absorption as the quantity of ECW was greater under the DS condition. Oosterhuis et al (1991) concluded that an increase in leaf ECW production for cotton was associated with decreased foliar-applied chemical penetration.…”

Influence of atmospheric CO2 enrichment, soil N, and water stress on needle surface wax formation in Pinus palustris (Pinaceae)

“…Jordan et al (1984) reported that sorghum leaf wax densities Ͼ 0.07 g/m 2 were effective in reducing cuticular water loss under most conditions. Water-stressed cotton leaves were found to have altered wax composition, greater cuticle thickness, and increased wax content, which collectively decreased penetration of chemical leaf defoliant (Oosterhuis, Hampton, and Wullschleger, 1991). Bondada et al (1996) found that water-stressed cotton leaves had altered wax composition and increased wax content (leaves, bolls, and bract), but no discernible changes in wax morphology were observed.…”

Sequential Applications of Synthetic Auxins and Glufosinate for Escaped Palmer Amaranth Control

“…Dicamba and 2,4-D are systemic herbicides and efficacy is dependent on translocation within the plant [35]. Larger plants may have thicker plant cuticles which could reduce herbicide penetration resulting in poor control [27,36,39]. Furthermore, mature plants have reduced sugar transport which may decrease translocation of some systemic herbicides [34,40,41].…”