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The tobacco budworm, Chloridea (Heliothis) virescens (F.), has evolved resistance to numerous insecticides in the field. In tobacco, chlorantraniliprole can be applied as either a preventative systemic soil application at or near transplant, or a foliar application timed to current treatment thresholds. With a novel mode of action chlorantraniliprole provides an option for rotation with other insecticides to reduce the probability of insecticide resistance development. However, specific usage patterns in tobacco have the potential to increase the risk of resistance development to this insecticide. In particular, soil applied treatments may expose C. virescens to sublethal concentrations of the insecticide. We studied chlorantraniliprole susceptibility in nine field populations and one laboratory strain of C. virescens using a diet incorporation bioassay. Mortality was measured at 7, 10, and 14 d after exposure. Our results demonstrated that bioassays should be evaluated at 14 d after exposure to optimize interpretation of the dose–response due to the antifeeding properties of chlorantraniliprole. We observed low variation within field-collected populations. Field populations were as susceptible as the laboratory strain; the resistance ratio at the 14-d evaluation for field-collected populations ranged from 1.01 to 1.05. A discriminating dose of 0.117, 0.080, and 0.070 μg a.i./g diet could be used at 7, 10, and 14 d, respectively. Larval growth varied between field populations. Two field populations continued growing on diet containing chlorantraniliprole and differed in size from the laboratory and other populations. Further evaluation of growth inhibition will be necessary. [ABSTRACT FROM AUTHOR]

Phytophthora nicotianae causes devastating disease in a range of hosts, including tobacco ( N. tabacum L.), tomato, citrus, strawberry, and numerous ornamentals. Black shank, caused by P. nicotianae , is the most economically important disease to tobacco production in Tennessee and North Carolina. Black shank management includes the use of resistant cultivars, crop rotation, and fungicides. Fungicide resistance is a concern for black shank management due to the limited number of active ingredients available and the repeated exposure of pathogen populations to these products. In vitro fungicide sensitivity assays were conducted on 155 P. nicotianae isolates collected in Tennessee and North Carolina in 2021 and 2022 to determine their EC 50 values for oxathiapiprolin, mandipropamid, and fluopicolide. The P. nicotianae was isolated predominantly from burley, dark, and flue-cured tobacco showing symptoms of black shank as well as tomato with buckeye rot symptoms. A discriminatory dose was used to determine each isolate's sensitivity to mefenoxam in 2021 and 2022. In 2021, EC 50 values were determined for oxathiapiprolin, mandipropamid, and fluopicolide. In 2022, discriminatory doses based on EC 75 values were used to determine each isolate's sensitivity to these fungicides. All isolates from the 2 years were sensitive to mefenoxam, mandipropamid, and fluopicolide. One isolate in 2022 was moderately sensitive to oxathiapiprolin, while all other isolates were sensitive., Competing Interests: The author(s) declare no conflict of interest.