Evaluation of Nematic1Des/Insecticides for Sweet Potato, Wayne County, 1978

Abstract

Abstract The effects of fumigant and non-fumigant nematicides/insecticides on nematodes and soil insects, yield, and quality of sweet potatoes were studied in a deep Norfolk sandy loam (pH = 6.4; O. M. = 0.5%; sand = 85.2%, silt = 10.1%, clay = 4.7%) in Wayne County, NC. The site had been planted to sweetpotatoes in 1977 and soybeans in 1976; root-knot nematode larvae counts of ca. 100/500 cm3 soil were low on May, 1978. On Jun 7, plots were hilled, and Vernam 6EC herbicide (.66 pt/acre) was applied. On Jun 14, fumigants were injected with a single chisel at a depth of ca. 6 inches centered over the row using a self-propelled applicator. Soil temperature at 6-inch depth was 83°F, air temperature was 90°F, and soil moisture was 85.3% of field capacity. On Jun 28, granular formulations were uniformly applied with a “salt shaker#x201D;, and wettable powders were suspended in water and applied as a drench at a rate of ca. 500 gal/acre or were applied with transplant water. Granular materials and drenches were applied to a 12-inch band over row centers, and within an hour incorporated to a depth of ca. 6-8 inches using a rototiller. Soil temperature at a 6-inch depth was 88°F, air temperature was 95°F, and soil moisture was fairly dry (77.6% of field capacity). On Jul 24, at layby, granular materials were uniformly applied to a 12-inch band over plant canopy using a “salt shaker#x201D;. Plots were single rows, 50-ft long, on 40-inch spacing. Treatments were replicated in four complete randomized blocks with 10-ft alleys between replications. On Oct 23, twelve soil borings (2 to 12-inch horizon) were taken from the root zone of each plot, composited, assayed for nematodes (extracted by the elutriation-centrifugation technique) and identified. On Oct 24, roots were harvested, graded into U.S.D.A. size grades (Jumbo, No. 1, Conner), and weighed; fifteen roots (5 canner, 5 small and 5 medium No. 1) were removed from each plot and rated for nematode, wireworm, white grub, and flea beetle damage; internal nematode infection was counted by slicing ca. 40% of the distal portion of each root in 2-mm sections and counting internal lesions. Weather during growing season was dry, and plants were under moisture stress in late summer. There was no water injury to roots at harvest as had occurred in previous years.