Efficacy of selected insecticides against the two-spot cotton leafhopper <i>Amrasca biguttula</i> (Hemiptera: Cicadellidae) on <i>Hibiscus rosa-sinensis</i> , 2026

The two-spot cotton leafhopper (TSCL), Amrasca biguttula, is an emerging invasive pest of ornamental crops in the southeastern United States, where feeding by adults and nymphs causes hopperburn and reduces plant quality and marketability. This study provides the first U.S. field evaluation of insecticides for managing TSCL on hibiscus, assessing the efficacy and residual performance of several IRAC groups under field nursery conditions. Hibiscus plants (H. rosa-sinensis ‘Hot Shot') of uniform size and age were obtained from a commercial nursery on 22 August 2025 and planted into 5-gallon pots containing a commercial substrate. Plants were maintained outdoors on a nursery pad at the Clemson University Pee Dee Research and Education Center (Florence County, SC). Plants were placed under protective netted tents to reduce interference from natural enemies and rainfall while remaining fully exposed to ambient temperature [average ≈ 82°F (28°C)], humidity (average = ≈ 75%), wind, and sunlight. TSCL infestations were established by placing infested cotton branches onto hibiscus plants weekly for two months. All flower buds and older leaves were removed to promote vegetative growth. Plants were irrigated on an alternate-day schedule and received one liquid fertilizer application during the season. Treatments were arranged in a randomized complete block design with six replicates, and each replicate consisted of three leaves sampled from the top, middle, and bottom canopy positions. Adult and nymph counts were recorded independently at the top, middle, and bottom canopy positions. Positional values were kept separate during data entry. Foliar sprays were applied to wet foliage using a CO2-pressurized backpack sprayer operated at 30 psi and equipped with a TeeJet XR 8002VS flat-fan nozzle. The first application was made on 13 Oct 2025. After the first application, conditions were: ambient temperature 78°F (25.5°C), relative humidity 74%, soil temperature (1.6 in) 91°F (32.5°C), canopy temperature 87°F (30.7°C), and wind 7 mph from the north. Treatment pots were positioned apart from untreated pots to reduce spray drift. The second application was made on 10 Nov 2025, exactly 28 days after the first application. After the second application, conditions were: ambient temperature 52°F (11.1°C), relative humidity 41%, soil temperature (1.6 in) 54°F (12.2°C), canopy temperature 52°F (11.0°C), and wind 12 mph from the west. Adults and nymphs were counted visually using a hand lens before treatment and again at 7, 14, 21, 28, and 35 days after the first treatment (DAT). Data at each post-treatment sample date were analyzed using one-way ANOVA. When significant treatment effects were detected (P &amp;lt; 0.05), treatment means were separated using Fisher's LSD test, and values are presented as means ± standard error. Before the first treatment, adult and nymph densities did not differ among treatments (Tables 1-2). At 7 DAT, significant differences were detected for both adults and nymphs. Adult counts were lowest in Hachi Hachi, followed in order of suppression by Talstar, Altus, Safari, Ventigra, and Mainspring, all of which differed from the nontreated control (Table 1). Nymph suppression was strongest in Hachi Hachi, followed by Talstar, Altus, Safari, and Ventigra, while Mainspring provided weaker nymph suppression (Table 2). At 14 DAT, treatment differences remained significant. Hachi Hachi and Altus maintained the lowest adult densities, and Hachi Hachi and Safari maintained the lowest nymph densities, while Mainspring showed a rebound in both life stages. Safari, Ventigra, and Talstar continued to provide consistent suppression (Tables 1 and 2). At 21 and 28 DAT, representing the extended residual period following the first spray, significant treatment differences persisted. Hachi Hachi, Altus, Safari, Ventigra, and Talstar maintained low adult and nymph densities through 28 DAT. Mainspring exhibited limited residual activity, with higher counts than other treated plants. The nontreated control consistently had the highest densities. At 21 and 28 DAT, representing the extended residual period following the first spray, significant treatment differences persisted. Hachi-Hachi SC and Safari maintained the lowest adult and nymph densities at both time points, while Altus and Ventigra also provided sustained suppression but at slightly higher levels. Talstar maintained moderate suppression, with adult and nymph densities higher than the strongest treatments at 21 DAT, but improved performance by 28 DAT. Mainspring exhibited limited residual activity, with consistently higher densities than other treated plants. The nontreated control had the highest densities throughout. A two-spray program spaced 28 days apart maintained suppression for six weeks, aligning with the final month and a half before plants flower and are prepared for shipping and sale. Maintaining low TSCL populations during the pre-shipping period is important due to regulatory concerns and spread risk, and we used a 28-day reapplication interval because it reflects common nursery practice and reduces labor and application frequency.