Drip Chemigation of Diamides and Neonicotinoids in Tomato, 2015*

This study was conducted at the Mountain Horticultural Crops Research Station in Mills River, NC. Five-week-old ‘Mountain Majesty’ tomato transplants were set on 27 May on black plastic mulch with drip irrigation. Plots consisted of 32.5-ft-long double rows with tomatoes planted in a 25-ft section (i.e., plots were 0.008 acres each). Rows were on 5-ft centers with plants spaced 1.5 ft within rows. Treatments were replicated four times and arranged in an RCB design. Tomatoes were staked and strung as needed and sprayed with a standard fungicide program. A CO₂-powered injection system in which insecticide treatments were delivered to the drip tube of individual plots through 1-inch poly tube was used to make treatment applications. Treatments were applied during a 15-min injection period, which was equal to the time it took water to travel from the point of injection to the furthest drip emitter (which was calibrated by injecting dye into the system). Following the injection period, the irrigation was run with water-only for a period equal to the injection time plus 10 min to ensure that all chemical was flushed from the drip lines. Treatments, rates, and application dates are listed in the tables. Insect populations were counted weekly: FT were monitored by removing 10 flowers per plot, placing them in a vial of 50% ETOH, and counting dislodged adults and immatures under a stereomicroscope. PA were monitored by recording the number of apterous aphids on 10 terminal trifoliate leaflets per plot. TSSM were counted by examining 10 terminal leaflets per plot. Season cumulative thrips, aphid, and mite days were calculated by multiplying the average insect density by sample interval (days) and summing values for each date. On 6 and 20 Aug and 3 and 17 Sep, mature fruits were harvested from the 10 middle plants of each row and assessed for damage. Data were transformed by square root (x + 1), subjected to two-way ANOVA, and means were separated by LSD (P ≤ 0.05). Data presented are back transformations.

FT populations were relatively low and consisted primarily of Frankliniella tritici (approximately 94% of collected specimens were F. tritici, 1% fusca, <1% occidentalis, and 5% in too poor condition to identify). Populations reached their peak densities in flowers on 21 Jul, averaging 10.8 thrips per 10 flowers in the check (Table 1). There were no differences among plots on any sample date. PA populations were extremely low until mid-Sep. By 24 Sep, populations had reached a high of 28.5 aphids per 10 trifoliate leaflets in the check. The Coragen/Sivanto, Coragen/AdmirePro/Venom, and 6-wk cyclaniliprole treatments (applied on 26 Jun and 7 Aug) significantly reduced populations below the check, although there were no significant differences among plots when cumulative aphid days were calculated (cumulative data not shown). TSSM populations began to increase in early Aug, reaching a high of almost 30 mites per leaflet in the check on 25 Aug. Cumulative mite days ranged from 1,153 in the 4-wk cyclaniliprole treatment to 2,314 in the Verimark treatment, but none of the differences were statistically significant (cumulative data not shown). The only differences occurred on 28 Jul and 18 Aug when only the cyclaniliprole treatments significantly reduced populations below the check.

Total yield from the 4 harvest dates averaged approximately 115 lbs of fruit across all treatments with no significant differences (Table 2). The untreated check had approximately 64% marketable fruit. The Coragen/AdmirePro/Venom treatment produced more marketable fruit (76%), though not significantly so, and the other treatments produced less (52–61%). Much of the fruit was categorized nonmarketable due to SB damage, which was found in 16% of check fruit but in significantly higher percentages in the Coragen/Sivanto (27%), Verimark (30%), and cyclaniliprole (23 and 32%) treatments. Only the Coragen/AdmirePro/Venom treatment significantly reduced SB damage (7%). Lepidopteran damage, including that from loopers, was fairly low, with only 6.3% of check fruit affected. This was higher than the treated plots, but not significantly. FT damage was relatively low (5% in the check) and did not differ significantly among plots. Damage assigned to the “other” category, primarily due to disease or physiological issues, averaged about 9% across all plots with no significant differences.

There were no differences in the amount of lepidopteran or FT damage among plots on any sample date (Table 3). There were always differences in the amount of SB damage, with the treatment receiving Venom consistently providing the highest control. Overall SB damage was fairly constant throughout the 6-wk harvest period, except for 3 Sep, which had at least twice the level of damage as the other harvest dates.

Author notes