No abstract

Two watersheds were treated with one application of 2,4,5,T + picloram (1:1) at 1.12 kg/ha while one other watershed was treated for 2 consecutive years at the same herbicide rates. Residues of 2,4,5‐T were reduced to trace levels [<10 parts per billion (ppb)] in soils 7 days after application at one location, after 28 days at the second, and after 56 days at the third. Residues of 2,4,5‐T were not detected below 15 cm and usually remained in the surface 2.5 cm of soil. Picloram was reduced to trace levels within 56 to 112 days after application, was not detected deeper than 60 cm, and was usually restricted to the surface 15 cm of soil. There was no evidence of subsurface lateral movement of either herbicide. Surface runoff water contained trace amounts of residue following storms for about 30 days after application. There was no evidence of residue carry over into the second year after treatment in water, soils, or vegetation. Monitoring of cumulative residues in water, soils, and vegetation showed that about 75% of the picloram was dissipated from the ecosystem within 28 days after application and over 90% was lost after 112 days.

We investigated the forces involved in the adsorption and desorption of 4-amino-3,5-6-trichloropicolinic acid (picloram), 1,1-dimethyl-4,4′-bipyridinium ion (paraquat), and α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) using cationic, anionic, and nonionic exchange resins. The anionic resin (Cl-form) adsorbed 375, 0.08, and 0.67 mg of picloram, paraquat, and trifluralin, respectively, per gram of oven-dry resin. The nonionic resin adsorbed 4.0, 0.34, and 10.0 mg of picloram, paraquat, and trifluralin, respectively, per gram of oven-dry resin, while the cationic resin (H-form) adsorbed 2.3, 226, and 0.17 mg of picloram, paraquat, and trifluralin, respectively. Other cationic resins (Na-form and Ca-form) performed similarly to the hydrogen form. Desorption studies indicated that picloram was adsorbed mainly in the anionic form by coulombic forces (electrostatic) and to a lesser degree by weak physical bonding (van der Waal's forces). Paraquat was adsorbed as a cation through coulombic forces. Trifluralin was mainly absorbed by physical bonds at sites on the resins where there were no coulombic forces.

Three blended foam adjuvants increased 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] uptake from aqueous solutions by detached live oak (Quercus virginianaMill.) leaves as compared to uptake from water alone. There were no differences in honey mesquite [Prosopis juliflora(Swartz.) D.C. var.glandulosa(Torr.) Cockerell] control with 2,4,5-T or 1:1 combinations of 2,4,5-T with picloram (4-amino-3,5,6-trichloropicolinic acid) or with dicamba (3,6-dichloro-o-anisic acid) at 0.56 kg/ha whether applied in water + 0.5% (v/v) foam adjuvant or in a diesel oil: water (1:4, v/v) emulsion. Residual life of picloram in native forages was not extended by foam carrier as compared to water, water and surfactant, and diesel oil:water emulsion as carrier. Foam generation from adjuvants with expansion ratios (ER) of two to four was less susceptible to alteration from addition of commercially-formulated herbicides than was an adjuvant with an ER of seven. Foam adjuvant ER's increased in a curvilinear fashion as water temperature was increased from 5 to 50 C.