A COMPARISON OF CHEMICAL AND CULTURAL CONTROL OF WEEDS IN IRRIGATION DITCHBANKS

Abstract

A study was conducted to compare the efficiency of various herbicidal treatments and cultural methods for control of weeds in a series of irrigation ditches similar in design to farmer head ditches. The residual herbicides, applied at soil sterilant rates, atrazine (22.4 kg/ha), bromacil (15.2 kg/ha), monuron (38.5 kg/ha), and simazine (22.4 kg/ha), were reapplied during September of 1973 to the same ditches that had received similar treatments in September of 1970. The foliar herbicidal applications of paraquat (2.2 kg/ha), dalapon + amitrole-T (11.2 + 2.2 kg/ha), paraquat + diquat (1.1 + 1.1 kg/ha), as well as growth retardent chlorflurenol (3.6 kg/ha), were applied annually each June from 1971 until 1976. Cultural control methods consisted of sowing (in 1971) the ditch bottoms and sides with streambank wheatgrass, sheep fescue, Russian wild ryegrass, and dwarf timothy. Over the period 1973–1976, the soil-applied herbicides gave good control of weeds in the ditches, with simazine and atrazine being superior to monuron and bromacil. The transport of these herbicides in the initial water flush and their leaching into the soil profile were shown to be potential hazards for contamination. The foliar herbicides paraquat and paraquat + diquat and to lesser extent amitrole-T + dalapon provided yearly suppression of weeds (following the third annual application in 1973) which allowed satisfactory water flow. Trace amounts of amitrole and dalapon were noted in the irrigation water immediately after herbicide treatment. The growth retardant was unsuitable for weed control since suppression was poor and adequate water flow conditions were observed only during the final year of the study. The grasses allowed good water flow and satisfactorily controlled weeds along the ditch side and bottom. However, some species required a period of 2 to 3 yr to become established whereas others were satisfactory for the first 3 to 4 yr only, suggesting that a mixture may be more suitable.