Translocation of¹⁴C-Glyphosate in Soybeans (Glycine max) and Johnsongrass (Sorghum halepense)

Abstract

Absorption and translocation of14C-glyphosate [N-(phosphonomethyl)glycine] in johnsongrass [Sorghum halepense(L.) Pers.] and soybeans [Glycine max(L.) Merr. ‘Lee 68’] were evaluated under various environmental conditions. The toxicity of unlabeled glyphosate applied similarly was determined in soybeans under similar conditions. In johnsongrass, absorption of14C-glyphosate nearly doubled and translocation increased as air temperature increased from 24 to 35 C. Translocation in johnsongrass and soybeans was often greater at a relative humidity (RH) of 100% than at 45% and at a soil moisture level of 20% (field capacity) than at 12% (near the wilting point). In soybeans, absorption of14C-glyphosate increased about 100%, translocation increased between 100 and 1200%, and glyphosate toxicity increased more than 200% as temperature decreased from 35 to 24 C. At 35 C, translocation in soybeans was often greater at 20% than 12% soil moisture. Absorption of14C-glyphosate in soybeans was greater when the herbicide was applied to mature rather than immature leaves and stems, but the age of the treated tissue had less effect on14C translocation. The addition of surfactant plus KH2PO4to the treatment solution increased glyphosate absorption and translocation in soybeans, but addition of surfactant alone reduced translocation and addition of KH2PO4alone increased translocation. Injury to six soybean cultivars from application of unlabeled glyphosate at 0.4 kg/ha ranged from 37% to 95% while total absorption of14C-glyphosate into treated leaves of the same six cultivars ranged from 23% to 74% of the amount applied.

Effect of environment and formulation on the absorption and translocation of fenridazon in wheat (Triticum aestivum L.)

“…Similar humidity effects on absorption of postemergence herbicides have been reported [3,5,8] . These results are often explained by the effect of humidity on (1) the biosynthesis and deposition of leaf waxes, (2) the hydration state of the leaf cuticle, or (3) the spray solution on the leaf surface .…”

“…As in the time-course experiment, an increase in temperature from 4'C to 24'C increased the total foliar absorption of fenridazon (Table 1) . Other researchers have found absorption of glyphosate increases with temperature [5,6,8] .…”

Investigating the mechanisms of glyphosate resistance in Lolium multiflorum

“…In contrast, in the S and in the SF populations, a greater percentage of 14 C-glyphosate moved to non-treated leaves and the stem. Because glyphosate tends to be actively phloem transported and accumulates in meristematic tissue (Sprankle et al 1975;McWhorter et al 1980;Arnaud et al 1994), the different translocation pattern in the OR population and other L. rigidum populations is associated with glyphosate resistance. 14 C-glyphosate translocation patterns between the SF and the S populations were similar at 48 h but different at 24 and 72 h after treatment.…”

Temperature influences the level of glyphosate resistance in barnyardgrass (Echinochloa colona)

“…Environmental factors have an impact on glyphosate activity and may affect the expression of glyphosate resistance in plants . Of these various factors, temperature has been demonstrated noticeably to affect the absorption and translocation of glyphosate to vegetative organs of plants in a number of studies . In addition, a reduction in herbicide translocation in plants has been identified as one of the mechanisms of glyphosate resistance; these plants have included annual ryegrass ( Lolium rigidum ), Italian ryegrass ( Lolium multiflorum ), horseweed ( Conyza canadensis ) and Johnsongrass ( Sorghum halepense ) .…”