Influence of Water Quality and Coapplied Agrochemicals on Efficacy of Glyphosate

Experiments were conducted in 2008, 2009, and 2010 to determine the influence of water source as carrier and other agrochemicals on glyphosate efficacy and physicochemical compatibility. Glyphosate efficacy was not affected by most water sources, when compared with deionized water, although response was not consistent across all weed species, including cereal rye, common lambsquarters, common ragweed, goosegrass, Italian ryegrass, large crabgrass, Palmer amaranth, tall morningglory, and wheat. Control by glyphosate was not negatively affected when coapplied with cloransulam-methyl, dicamba, flumioxazin, pyrithiobac-sodium, thifensulfuron-methyl plus tribenuron-methyl, trifloxysulfuron-sodium, and 2,4-D but was affected by acifluorfen and glufosinate. Calcium, manganese, and zinc solutions consistently reduced weed control by glyphosate, whereas boron seldom affected efficacy. Compared with deionized water, Italian ryegrass control was affected by water sources when applied at seedling and jointing stages more so than at tillering and heading growth stages. Calcium, manganese, and zinc reduced control regardless of growth stage. Precipitates were not produced when glyphosate was applied with the water sources or fertilizer solutions. However, transient precipitates developed when glyphosate was coapplied with cloransulam-methyl, flumioxazin, thifensulfuron-methyl plus tribenuron-methyl, and trifloxysulfuron-sodium but not when coapplied with acifluorfen, dicamba, glufosinate, pyrithiobac-sodium, and 2,4-D. Solution pH ranged from 4.11 to 5.60 after glyphosate was added, regardless of solution pH before glyphosate addition. Nomenclature: 2,4-D; acifluorfen; boron; calcium; cloransulam-methyl; dicamba; flumioxazin; glufosinate; glyphosate; manganese; pyrithiobac-sodium; thifensulfuron-methyl plus tribenuron-methyl; trifloxysulfuron-sodium; zinc; cereal rye, Secale cereale L.; common lambsquarters, Chenopodium album L.; common ragweed, Ambrosia artemisiifolia L.; goosegrass, Eleusine indica (L.) Gaertn.; Italian ryegrass, Lolium perenne L. ssp. multiflorum (Lam.) Husnot.; large crabgrass, Digitaria sanguinalis (L.) Scop.; Palmer amaranth, Amaranthus palmeri (L.) S. Wats.; tall morningglory, Ipomoea purpurea (L.) Roth; wheat, Triticum aestivum L.