Studies were conducted to compare the effects of low-volume applications to conventional high-volume applications on the phytotoxicity of selected herbicides to purple nutsedge (Cyperus rotundus L.). Two field experiments were conducted in 1990. One experiment involved the effects of herbicides applied post-directed on a band to purple nutsedge in cotton. The other experiment was conducted to determine the effects of herbicides applied broadcast over-the-top to purple nutsedge alone. Low-volume applications were applied at the broadcast rate of 2 gallons per acre (gpa) with the herbicides in either the light weight paraffinic oil, Orchex 796, or in an invert emulsion composed of the following proportions: a light-weight paraffinic oil, AC-100 (3 ml), ortho X-77 nonionic surfactant (3 ml), lecithin (4 ml), and lanolin (3 ml). Each herbicide plus Agri-dex (83% paraffinic oil and 17% polyoxyethylene fatty acid ester) was added to the above mixture to make a total volume of 20 ml. Then water (20 ml) and Orchex 796 (10 ml) were added separately and stirred after each step. High-volume applications were applied at the broadcast rate of 20 gpa in water containing 0.25% (v/v) nonionic surfactant, Ortho X-77.

In the post directed experiment, cotton was 12 to 15 inches tall and purple nutsedge was 7 to 9 inches tall. The herbicides and broadcast rates were: fluridone, 0.3 lb/A; glyphosate 1.0 lb/A; MSMA, 1 lb/A; and norflurazon 0.5 lb/A. The low-volume applications were on a 14-inch band and the high-volume applications were on a 20-inch band.

In the broadcast experiment, purple nutsedge was 12 to 15 inches tall growing in an open field. Treatments were made with the same diluents and application volumes as with the directed sprays with glyphosate and MSMA at 1lb/A as before, and norflurazon increased to 1 lb/A. Treatments were made to plots 80 inches wide and 40 feet long

In post-directed treatments at 4 weeks after treatment (WAT), purple nutsedge control was greater with glyphosate and MSMA when applied in oil or invert emulsion (<89%) than when applied in water (<75%) diluent. With low-volume applications glyphosate injured from glyphosate int he high-volume, water diluent and no cotton injury from fluridone and norflurazon at either low- or high-volume application. Yield of seed cotton was decreased 23 and 31% with the applications of glyphosate in the low-volume oil and ivert emulsion diluents, respectively.

At 2 WAT, broadcast treatments to purple nutsedge alone yielded similar results as the directed sprays. Control with glyphosate applied in the low-volume invert emulsion and the oil diluent was as good as when applied in the high-volume water diluent (71 to 75% control of purple nutsedge with water, oil and invert emulsion diluents, respectively. Norflurazon, as with the post-directed treatments, was not effective when applied broadcast with 11 to 18% control with the different diluents and spray volumes of this study.