Cabbage Flea Beetle Insecticide Trial, 2016* Open Access

The purpose of this experiment was to compare the efficacy of various soil-applied systemic insecticides for FB control, as well as to assess the performance of transplant tray versus post-planting drench applications of Verimark (cyantraniliprole) for lepidopteran control on cabbage. The trial was conducted at the Mountain Horticultural Crops Research Station, Mills River, NC. Five-week -old “Bravo” cabbage transplants were set in bare ground on 29 Jul. Plots consisted of two 25-ft long rows on 3-ft centers with plants spaced 15  inches apart within rows. A non-treated row separated treatment rows. Treatments were arranged in a RCB design with -->four replications. Except for Brigade, insecticides were applied either as transplant tray treatments 3  d before planting (26 Jul), or as transplant water drenches at planting (29 Jul) (see tables for materials and application methods). Transplant drench applications were made by pouring 8 oz of insecticide/water solution to the soil of each plant at planting. The single foliar application of Brigade for FB control was made with a CO₂ backpack sprayer delivering 30 gpa through a single hollow-cone nozzle (D4 disk, #45 whorl) at 35 psi on 6 Aug. Beginning approximately 11  d after planting, FB were counted weekly on 10 plants per plot, and each of the 10 plants was rated for FB damage based on the percentage of area injured on the first fully expanded leaf. Severity of damage was rated from 1 to 4, with 1 = 0–5% damage, 2 = 6–25%, 3 = 26–50%, and 4 = 51–100%. On three sample dates, a minimum of 20 FB were collected from border rows and identified to species.

All neonicotinoid treatments were sprayed with Avaunt (3.5 oz/acre) on 5 Sep for control of lepidopteran larval pests, followed by Radiant (6.0 fl oz/acre) on 16 Sep. Brigade was applied to the standard treatment. Weekly sampling for lepidopteran larvae (CL, ICW, and CSCW) occurred from 6 Sep to 4 Oct by examining 10 plants from each plot and recording the total number of larvae. All data were subjected to two-way ANOVA and means were separated by LSD (P = 0.05).

Phyllotreta albionica and Phyllotreta striolata were the two FB species infesting plots, with P. striolata accounting for about two-thirds of all beetles (Table 1). On the first sample date, 11 d after planting (DAP) and 3 d after the foliar Brigade treatment, the only treatments to significantly reduce total FB counts were the 13.5 fl oz/acre rates of Verimark (both transplant tray and drench applications) and the Venom drench treatment (Table 2). Surprisingly, the foliar application of Brigade did not reduce FB populations. By 18 DAP, none of the treatments had significantly fewer flea beetles than the control, although numbers were lowest in the Venom treatment. Also, the FB counts in the Verimark transplant tray and transplant drench treatments were significantly higher than the check on 23 Aug.

Despite the high FB counts in several of the Verimark treatments, feeding damage was consistently low on all sample dates, suggesting that Verimark-treated plants were not palatable to beetles (Table 3). The high beetle counts in these treatments may have been due to the fact that Verimark-treated plants were more attractive to beetles due to less damage. Damage ratings were also low in the Venom treatment during the first 18 DAP, but when the residual activity of Venom declined and beetle counts increased, so did damage levels.

When lepidopteran larval populations were first sampled on 6 Sep, there was no difference in the number of CL in any of the Verimark treatments versus the check (Table 4). Although looper densities naturally declined thereafter, season total counts indicated that the Avaunt, Radiant and Brigade treatments were all effective against this looper population. The 6.75 fl oz rate of Verimark applied as a transplant tray treatment was the only treatment that did not significantly reduce ICW below the check (Table 5). CSCW were present in relatively high numbers in all Verimark treatments by late Sep (Table 6), and the Verimark treatments were the only treatments not to reduce season total numbers below the check.

Author notes