Petroleum Oils for Management of the Sweetpotato Whitefly and Geminivirus on Fresh Market Tomatoes in West-Central Florida, Fall, 1990

Abstract

Abstract On 10 Sep, transplants were set 18 inches apart on raised beds of EauGallie fine sand covered with black polyethylene mulch. Plots consisted of three, 25-ft-long rows on 5 ft centers. Treatments were replicated 2 times in a randomized complete block design and were applied with a tractor-pulled sprayer on 12, 17, 24 Sep, 1, 8, 15, 22, 29 Oct, 5, 13, 19, and 26 Nov. Five petroleum oil products were applied at 200 psi using nozzles with standard D-3 disks and #25 cores. Two of the products were also applied at 400 psi using TX-5SS hollow cone nozzles made of stainless steel (equivalent to D-5 disks and #50 cores). The spray boom was fitted with a single drop between or on each side of each row. Thus, the normal spray width was 4 ft. For the first four applications, 1 ft extensions were added to the nozzles on the drops so that the spray swath width was 2.5 ft. For the 400 psi treatments, two nozzles were added to a cross boom in order to provide coverage on the tops of the plants. As the plants grew, the number of nozzles per row was increased in order to increase gallonage. For the 200 psi applications, 4 nozzles per row (2 on each side of each row) were used for the first five applications (80 gal/acre for the first four applications and 50 for the fifth when the spray swath was increased), 6 nozzles the next two applications (75 gal/ acre), and 8 nozzles for the remaining 6 applications (100 gal/acre). For the 400 psi applications, 6 nozzles per row (2 on each side of each row and 2 above each row) were used for the first 4 applications (85 gal/acre), 4 nozzles (two on each side of each row) for the fifth application (35 gal/acre), 6 nozzles (three on each side of each row) for the next two applications (50 gal/acre), and 8 nozzles (4 on each side of each row) for the remaining applications (70 gal/acre). JMS Stylet Oil was applied at 0.5 gal/100 gal for the first 3 applications and at 0.75 gal/100 gal for the remaining applications. The terminal leaflet was collected from the 7th or 8th leaf (counting from the top) of each of ten stems from the middle row of each plot on 23 Oct and 20 Nov and the numbers of eggs, crawlers, sessile nymphs, and pupae of the sweetpotato whitefly were counted. On 21 Sep, 2, 17 Oct, 2, 9, and 20 Nov, the numbers of sweetpotato whitefly adults were counted on the undersides of three leaves randomly selected from the top, middle, and bottom of each of 10 plants per plot. The numbers of plants in each plot infected with geminivirus were determined on 20, 27 Sep, 4, 12, 18, 24 Oct, 1, and 8 Nov. All fruit of marketable size were harvested on 15 Nov, 5, and 18 Dec and the fruit were counted and weighed. Samples of 50 fruit from each plot and harvest were held at room temperature in paper bags. As the fruit ripened, each was rated 1 to 4 for increasing severity of external symptoms of irregular ripening (IRR). This disorder is associated with high populations of the sweetpotato whitefly and is characterized by inhibited or incomplete ripening of longitudinal sections of fruit. The percentage of unmarketable fruit was calculated with fruit rated 3 or 4 as unmarketable. Percentage data were transformed to arcsine of the square root of the proportion before analyses but are presented in the original scale.