The herbicidal activity of haloxydine in some Manitoba soils
McMillan, Alan Duncan
Haloxydine, an experimental herbicide was tested in the field for selective control of broad-leaved and grassy weeds in wheat Triticum aestivum L., barley Hordeum vulgare L., flax Linum usitatissimum L., rape Brassica napus L. and potatoes Solanum tuberosum L. Applications of 280 g/ha of haloxydine controlled weeds at some locations with barley, flax and rape not showing any phytotoxicity, however wheat stands were reduced by 30%. Rape and flax were tolerant to applications of haloxydine of 840 g/ha. Potatoes were severely damaged by applications of 560 g/ha and 1120 g/ha at Carman but not at Carberry. Post-emergent treatments were more effective than pre-emergent treatments in controlling weeds. Weed control ranged from nil to excellent from one site to another. This was attributed to variations in soil properties. A comparison of formulations of haloxydine at Carman indicated the ester form had less biological activity than the potassium salt. Haloxydine residue trials were established in the fall of 1969. A field bioassay was conducted in the spring of 1970 using wheat, flax, rape and alfalfa Medicago sativa L. Rape was the only crop that could be safely grown following fall application of haloxydine. Persistence and movement of haloxydine applied in the fall was studied. Samples collected 18 and 68 days after application indicated a 100% recovery of haloxydine and maximum movement to a depth of 15 and 23 cm in a clay soil and a sandy loam soil, respectively. Samples collected the following spring indicated an 80% recovery and no downward novement during the intervening winter. One year after application, haloxydine had penetrated to a depth of 45 cm in the sandy loam soil but no further movement had occurred in the clay soil. After one year, 42% to 77% of the haloxydine persisted in the sandy loam soil and 21% to 68% in the clay soil, with high rates having a greater percentage degraded. A bioassay of haloxydine-soil type interaction indicated ED50 values of 0.125 ppm to 0.993 ppm. Multiple regression analysis using the variables cation exchange capacity, organic matter, % sand, % silt, % clay on observed ED50 values yielded an R2 = .9322. The best signle variable was cation exchange capacity with R2 = .8072. Cation exchange capacity plus clay had an R2 = .9270. However, organic matter plus sand with an R2 - 0.8745 is preferred since clay is highly correlated with cation exchange capacity. The use of three variables, cation exchange capacity (C.E.C.), sand and silt yields an equation predicting ED50 values of Y = 0.9794 + 0.0311 C.E.C. - 0.0101 sand + 0.0119 silt. These three variables are responsible for 99.96% of the total regression.