Effect of chemicals on vine kill,yield and quality of potatoes in the Red River Valley

Sodium arsenite at 9 lb, DNBP at 2.5 lb, diquat at 1 lb, paraquat at 0.5 and 1 lb and prep at 2 and 4 lb/acre were tested as vine killers for potatoes during 1963, 1964 and 1965. Based on ratings 1 or 2 days after spraying, 1 lb diquat, 1 lb paraquat and 2.5 lb/acre DNBP resulted in the quickest kill. Paraquat at 0.5 lb and sodium arsenite at 9 lb/acre were slightly slower. Prep at 2 and 4 lb/acre was consistently slowest. Some of the slower acting chemical gave equally good kill after 7 days. Chemical vine killing usually reduced yields and specific gravity by shortening the growing period. There was no effect from any of the chemicals on the color of potato chips. A slight amount of vascular discoloration did occur in tubers from all treatments. Vascular discoloration of tubers from vines treated with prep at 2 lb/acre was greater than that of tubers from vines which were cut and not sprayed. None of the vascular discoloration was severe enough to be economically important. In a second test sodium arsenite at 9 lb and diquat at 0.5, 1 and 2 lb/acre were applied as single and split applications in 1963. The major effect from the split applications was a slower rate of vine kill.