Control of Sweetpotato Whitefly With Insecticides on Staked Tomatoes, Fall 2014*

Sweetpotato whitefly biotype B continues to be the key tomato pest in Florida due to its role as vector of tomato yellow leaf curl virus (TYLCV). Seedlings of cv. ‘BHN-945’ obtained from a commercial greenhouse were transplanted at the Southwest Florida Research and Education Center in Immokalee Florida on 10 Sep. Plants were spaced 18-inches apart on 2 sets of 3 beds 420 ft in length and covered with white polyethylene film mulch after incorporating 50% of the expected nutrient requirement as 10-2-10 NPK dry fertilizer. The rest was injected during the course of the crop as liquid 7-2-7 through drip tapes (2 per bed) with 8 inch emitter spacing. The center row in each 3-bed section was left untreated as a buffer and source of pests. A RCB plot design was used consisting of four treated rows in each of four replicates and main plots of 24 plants each with four plants left between plots as buffers. Soil drenches of Admire Pro were made to all plants including the check on 15 Sep by delivering a 90-ml suspension per plant using an EZ-Dose^® sprayer operating at a pressure of 45 psi (Table 1). Foliar sprays (Table 1) were applied with a high clearance sprayer set up for single row operation at 180 psi and 2.3 mph. The sprayer was fitted with two vertical booms equipped with yellow Albuz^® hollow cone nozzles, each delivering 10 gpa. Total spray volume increased from 60 to 80 gpa as nozzles were added to accommodate plant growth (Table 1). Actigard 50 WG (Acibenzolar-S-methyl) at 0.33–0.5 oz/acre and Regalia (5% extract of Reynoutria sachalinensis) at 2 qts/acre were applied as needed for suppression of fungal and bacterial disease. Xentari DF at 1.5 lbs was applied 6, 20, 27 Oct and 3 in addition to Intrepid (8 oz/acre) on 13 Oct and 10, 17 Nov for control of lepidopteran pests.

Whitefly adults were monitored weekly 23 Oct to 19 Nov on five leaflets from one mid-canopy level true leaf taken from 10 plants per plot. Eight 0.5 inch square leaf discs were cut from each of three leaflets of one terminal 7th node trifoliate sampled on 23, 30 Oct and 6, 13 and 19 Nov from five plants per plot. Immature stages counted under a stereoscopic microscope. Fruit of marketable size were harvested from six plants in each plot on 3 and 11 Dec and culled for defects due to insect damage, uneven ripening, bacterial spot and surface deformities such as shoulder cracking and zippering. Number, size, and weight of marketable fruit were recorded. Data were subjected to ANOVA and means separated using LSD (P = 0.05).

No statistically significant treatment effects were observed with regards to the number of adults recorded on any of the sample dates (P = 0.19–0.73, data not shown). However, all treatments reduced the number of nymphs compared to the untreated check on 6, 13 and 19 Nov (Table 2). Differences among treatments included greater suppression of nymphs by Closer at 5 oz/acre compared to the plant extract on 6 Nov, by the standard compared to Closer at 3 oz/acre, Closer at 4 oz/acre alternated with Baythroid and plant extract on 13 Nov, and by Closer at 4 oz/acre alternated by Baythroid compared to Closer at 3 oz or plant extract on 19 Nov. Rate responses with Closer either alone or with Baythroid were inconsistent. Yields averaged 131.7 ± 4.0 (mean ± SE) marketable fruit per six plants weighing 55.8 ± 1.7 lbs with no significant treatment effect. No phytotoxicity was observed for any treatment.

Author notes