Evaluation of Trabon for the Control of Sweetpotato Whitefly, Bemisia tabaci, Infesting Indeterminate Greenhouse Tomatoes, 2017

The objective of this study was to evaluate the effect of Trabon EC (soybean oil) as a foliar spray against sweetpotato whitefly, Bemisia tabaci Biotype B, and compare it against the combined products Botanigard 22WP + PFR-97, two industry standards, (Beauveria bassiana Strain GHA + Isaria fumosorosea Apopka Strain 97). The experiment was conducted at a greenhouse at Ohio Agricultural Research and Development Center in Wooster, OH. On 17 Feb, the greenhouse was cleaned and disinfected; wire trellis systems were set up and grow bags hydrated. On 18 Feb tomato seedlings ‘Campari’, provided by Soave Agricultural Group from Kingsville, Ontario Canada, were transplanted into Golden Grow Hydroponics Premium Grow Bags from Projar, made of coco husk. Plots were arranged in an RCBD design with four replications. Each treatment consisted of three plants spaced 0.46 m apart with 1.2 m between rows. A drip irrigation system was set up at transplant and a greenhouse grade fertilizer (MGS SELECT Customized Soluble Nutrition) was injected every 6 h to the tomato plants at the rate of 1:100 by using a Dosatron D14MZ2 injector and emitter with a flow rate of 1.9 liters/h beginning 18 Feb and ending 9 Jun. For weight support and ease of pruning, trellis twine with hooks were hung from main wire lines and each plant was tied with trellis clips to the vine stalk on 20 Feb. The insecticide Spinosad at 0.44 liter/ha was applied on 27 Feb and 11 Apr to control thrips.

Treatments were applied using a backpack CO₂-pressurized sprayer (275.79 Kpa, 447 l/0.4 ha, 3.8 kph) beginning on 5 May and ending on 16 Jun for a total of seven applications. An RCBD design was used with four treatments, including an untreated check, and four replicates. Tomato plants were selected at random from each unit and were infested with whitefly eggs. On each selected plant, five leaflets were selected and six pairs (male:female) of sweetpotato whitefly adults were placed inside a plastic clip cage to prevent their escape. Whitefly adults were obtained from colonies maintained at the Canas lab. After 24 to 48 h, all the adults were removed to prevent plant cross-contamination. Once the adults were removed, all whitefly eggs on the leaflets were counted. The plants were ready for treatment once nymphs hatched from eggs. Before treatments started the total number of nymphs found was counted on each leaflet. For the duration of the experiment, five leaves were evaluated from each plant, and the number of SWF nymphs and adults was counted. All count data were analyzed via ANOVA and a Tukey’s test was used to separated means (α = 0.05). When necessary non-normal data were transformed using a Log (X + 10) transformation.

During each date, plants were evaluated for phytotoxicity. For this, we use a qualitative rating system that evaluated leaf damage and ranged from 0 to 10. Zero is the lowest number and indicates no leaf damage, and 10 is the highest indicating complete leaf burn in the whole plant. Because we included all leaf damage, the most important comparison is against the untreated check.

All treatments started with similar numbers of whitefly nymphs (Table 1).

Nymphs

There were no statistical differences between treatments 7 days after treatment (DAT) (Table 1). However, there was a numerical trend for all insecticide treatments to have fewer whitefly nymphs compared with the untreated check. At 14 DAT, similar results were observed. At 21 DAT, all treatments had statistically fewer whitefly nymphs than the untreated check. At 35 DAT, only the combined product had statistically fewer whitefly nymphs compared with the untreated check. At 42 DAT, all treatments had statistically fewer whitefly nymphs compared with the untreated check.

The results show that the combined treatment had the best nymph control followed by the two Trabon rates.

Adults

All insecticide treatments had numerically fewer whitefly adults than the untreated check at all dates evaluated (Table 2). At 21 DAT, all insecticide treatments had significantly fewer whitefly adults compared with the untreated check with the combined product having the fewest number of whitefly adults. At 28, 35, and 42 DAT all insecticide treatments had statistically fewer whitefly adults than the untreated check.

There was a numerical trend for the combined product to have fewer whitefly adults. However, this trend of fewer whitefly adults was not statistical different from the two Trabon rates except for one instance: the higher Trabon rate at 21 DAT.

Phytotoxicity

No phytotoxicity (from ratings) differences were observed between the untreated check and the treatments (Table 3). Also, all plants had similar size at the end of the experiment (Table 4).

In summary, in this experiment, all insecticide treatments significantly lowered the number of whitefly nymphs and adults compared with the untreated check. The combined treatment (Botanigard + PFR-97) had the best numerical nymph and adult control followed by the two Trabon rates, but these numerical differences were not statistical significant except in one instance.

Support for this project was kindly provided by Crop Protection Technologies PTE LTD, Singapore 658071.