Control of Sweetpotato Whitefly on Staked Tomatoes in Florida, Fall 2015*

Sweetpotato whitefly (SWF): Bemisia tabaci (Gennadius) Middle-East Asia Minor cryptic species 1 (MEAM1) also known as biotype B, continues to be the most important pest of tomatoes in Florida due to its role as vector of tomato yellow leaf curl virus (TYLCV). Thus, the necessity of testing new products and combinations, as well as monitoring those already in general use. Seedlings of ‘BHN-975’ obtained from a commercial greenhouse were transplanted at our center on 9 Sep. Plants were spaced 18-inches apart on a set of 3 beds 420 ft in length on 6 ft centers and covered with whiteface 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 was left untreated as a buffer and source of pests. On the remaining 2 rows, 4 replicates and 7 treatments were distributed in an RCB design among plots of 18 plants each with 2 plants left between as buffers. Soil drenches of one of 5 different systemic insecticides were completed on 9 Sep by delivering a 120 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. Movento applications included a non-ionic surfactant at 0.25% vol/vol. 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 to 0.5 oz/ac, Regalia^® (5% extract of Reynoutria sachalinensis) at 2qts/ac and Quadris Opti^® azoxystrobin + chlorothalonil @1.6 pts/ac were applied to all plants as needed for suppression of fungal and bacterial disease, as were Xentari^® DF (Bacillus thuringiensis aizawai) at 1.5 lbs weekly starting 12 Oct Nov for control of lepidopteran pests and Hero (10.3 oz)/Malathion (32 oz) 20 Nov and Baythroid (3.0 oz)+Malathion (32.0) oz 25 Nov to prevent whiteflies from emigrating to nearby plots (Table 2).

Whitefly adults were monitored weekly from 8 Oct to 19 Nov by carefully inverting five leaflets from one mid-canopy level true leaf of 8 plants per plot and counting all adults on the leaflet. Immature stages were counted under a stereoscopic microscope from 8, 0.5 in² leaf discs cut from each of three leaflets of one terminal 7th node trifoliate taken on 8, 15, 21 Oct and 2, 12, 19 Nov from 5 plants per plot. TYLCV incidence was evaluated on 13 Nov by rating each of 16 plants per plot as: (0) no visible signs of TYLCV, (1) one to three shoots with some visible symptoms, (2) four to ten shoots with virus symptoms, (3) more than ten shoots with some stunting observed, and (4) severely stunted plant. Number, size, and weight of marketable fruit were recorded from fruit of 4 marketable sizes harvested from 6 plants per plot on 10 Dec. Data were subjected to ANOVA and means separated by LSD (P = 0.05).

Adult numbers were low throughout the study with no suppression compared to the check seen until 15 Oct, 36 days after drench applications. Thereafter, significant differences were only seen on 12 Nov at which time treatments commencing with AdmirePro or Sivanto drenches showed significantly fewer adults than the untreated check. All treatments significantly reduced the number of nymphs compared with the check on 8, 15 Oct, and 2, 12 Nov with no differences among treatments. On 21 Oct, all treatments commencing with drenches containing dinotefuron (Scorpion, Venom, and Certador) were not different from the check and fewest nymphs were seen with Sivanto–Movento although not significantly different from Admire–Sivanto–Movento or Venom–Movento treatments. On 19 Nov, all treatments were providing significant control although less so with Certador–Movento than all other treatments except for Venom–Movento. All treatments provided significant reduction in TYLCV incidence compared to the untreated check. No symptomatic plants were seen among those treated with Admire–Movento, although incidence was not significantly different from Venom–Movento. TYLCV incidence with these latter two treatments was lower than in plants treated with Scorpion–Knack–Courier or Certador–Movento.

No significant differences in yield were found, with an average of 94.5 ± 15.2 fruit weighing 40.4 ±5.5 lbs from 6 plants per plot. No phytotoxicity was observed for any treatment.

Author notes