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

On 20 Mar, transplants were set 18 inches apart on raised beds of EauGallie fine sand covered with black polyethylene mulch. Plots consisted of three, 20-ft-long rows on 5 ft centers. Treatments were replicated 4 times in a randomized complete block design and were applied with a tractor-pulled sprayer on 6, 12, 17 Apr, 2, 8, 16, 22, 30 May, 5, 11, and 18 Jun. 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 Albuz— ceramic “brown” (equivalent to # 5 disk), hollow cone nozzles fitted with #80 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) 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 (100 gal/acre), 6 nozzles (three on each side of each row) for the fifth application (64 gal/acre), and 8 nozzles (4 on each side of each row) for the remaining applications (100 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 29 May and 27 Jun. The numbers of eggs, crawlers, sessile nymphs, and pupae of the sweetpotato whitefly were counted on the whole leaflet of the first sample and on a 16 mm leaf disk of the second sample. The number of plants in each plot infected with geminivirus was determined on 13, 20 Apr, 7, 11, 18, 24 May, 1, 8, 15, and 22 Jun. All fruit of marketable size were harvested on 12 and 25 Jun and the fruit counted and weighted. Samples of 50 fruit from each plot from each sample 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 percent of unmarketable fruit was calculated using fruit rated 3 or 4 as unmarketable. Percent data were transformed to the arcsine of the square root of the proportion prior to analyses but are presented in the original scale.