Uptake and translocation of 14'C-glyphosate in glyphosate-resistant cotton

ABSTRACT

H.M. Harris and W.K Vencill
Univ. of Georgia, Athens
Department of Plant Protection
Nanjing Agricultural University
Weed Science Society of America Abstracts
2000 Meeting of the Weed Science Society of America
Vol 40, 2000

Studies were conducted to ascertain the uptake and translocation of glyphosate when applied to glyphosate-resistant cotton as basal direct spray, a directed spray 33% up the stem, a single broadcast application, and a sequential broadcast application at match head square and first white flower growth stage. Glyphosate was applied at 1 kg ha-1 spiked with approximately 0.198 < l.c.muCi of 14C-glyphosate in 10 ml of solution per plant. Sequential applications were made ten days later. All plants were harvested five days after the last application, and plant parts were separated into vegetative and reproductive tissue per node, roots, stem, and terminal tissue. One-gram samples of dried plant materials were oxidized and counted using a LSC system. Four replications in a complete block design were used. Plants were grown in a controlled-environment glasshouse with 16-h photoperiod at 30/25 C temperature regime. Glyphosate uptake was similar between stages of growth when a directed base application was made. However, when glyphosate was applied 33% up the stem or applied broadcast to the whole plant either as a single or sequential application, glyphosate uptake at the match head square stage of growth was approximately twice that of glyphosate applied at the first white-flower stage. Less than 3% of absorbed glyphosate was translocated to the root, stem, or terminal of cotton with any with any glyphosate application method at at both growth stages. When glyphosate was applied to the base of two-leaf cotton, there was an even distribution of glyphosate amongst vegetative and reproductive tissue. However, when glyphosate was applied to the base of cotton at the match head square stage, approximately 70% was translocated to vegetative tissue. Applications of a single or sequential application of glyphosate broadcast or a single application 33% up the stem resulted in greater than 70% translocation of glyphosate to vegetative tissue at both stages of cotton growth. These data indicate that substantial levels of glyphosate are translocated to the reproductive tissues of cotton regardless of application type. (157A)