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.

Both purple nutsedge (Cyperus rotundusL. # CYPRO) and yellow nutsedge (C. esculentusL. # CYPES) are problem weeds in crops in many parts of the world. Yellow nutsedge is found in all U.S. states. Purple nutsedge is confined to the southern region of the United States, ranging from North Carolina across southern Arkansas and into southern California.

The effects of several inorganic salts on the toxicity and translocation of nonradiolabeled and14C-radiolabeled MSMA (monosodium salt of MAA) and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] following foliar applications to purple nutsedge (Cyperus rotundusL. ♯ CYPRO) were evaluated. Salts of the monovalent cations NH4+, K+, and Na+and to a lesser degree the anion PO4generally resulted in increased toxicity of these herbicides. Salts of the divalent and trivalent cations Zn++and Fe+++frequently reduced the activity of glyphosate and MSMA, whereas salts of the divalent Ca++ion caused little or no effect on activity. Salts of the anions Cl–, NO3–, CO3—-, and SO4–resulted in increased, decreased, or unchanged glyphosate toxicity as influenced by the associated cation. Translocation of the radiolabel of14C-glyphosate and14C-MSMA was increased by the addition of NH4Cl, while retention of the radiolabel within the tissue of the treated area was increased by the addition of FeCl3to the treated leaf surface.

Toxicity of nonradiolabeled and translocation of14C-labeled glyphosate [N-(phosphonomethyl)glycine] in cotton(Gossypium hirsutumL.) were evaluated under different environmental conditions as affected by surfactant and by the maturity of the plant tissue at the place of herbicide application. Toxicity was affected primarily by temperature with 21 to 40% greater cotton injury at 25 C than at 35 C. The addition of surfactant often increased toxicity under environmental conditions where toxicity was initially low. Absorption and translocation of14C was affected primarily by relative humidity (RH). At constant temperature and rate of surfactant, an increase in RH from 40 to 100% resulted in a 3- to 6-fold increase in translocation of14C. Autoradiograms indicated that the movement of the14C-label was primarily into leaves above the treated area. Translocation of14C was significantly greater following application to the mature lower stem than to the mature lower leaves or to immature upper stem or leaves of cotton.

Purple nutsedge(Cyperus rotundus L.)develops as a series of shoots connected by bulbs, rhizomes, and tubers. The leaves contain parallel, collateral vascular bundles with the majority of the photosynthetic cells concentrated in the sheathing girdle around each bundle. The upper leaf surface consists of a single layer of large epidermal cells covered by a thick cuticle. Stomates occur only in the lower surface. The vascular bundles vary from collateral to amphivasal as they pass from the leaves through the bulb into the rhizomes and tubers. Newly developing rhizomes and tubers appear white and fleshy with a parenchymatous epidermis and cortex. Mature rhizomes appear brown and wiry with a deteriorated outer cortex and a lignified inner cortext and endodermis. Tubers and bulbs form similarly at the rhizome apices with each accumulating starch. The interconnecting vascular system appears to remain intact throughout the growing season.