Influence of transplanting date and tobacco budworm (Lepidoptera: Noctuidae) treatment threshold density on flue-cured tobacco quality and yield and secondary pests

The influence of transplanting date and treatment thresholds for tobacco budworm, Heliothis virescens (F.), on leaf quality and yield of flue-cured tobacco, Nicotiana tabacum L., was examined in field plots during 1987-1989. Up to six insecticide applications were needed to maintain budworm population densities of less than one per 20 plants in the early-transplanted tobacco (late March). Fewer insecticide applications were needed to maintain this pest population density in the middle-(mid-April) and late-planted (late April) tobacco. Transplanting date and tobacco budworm treatment threshold level (1, 2, 4, or 8 budworms per 20 plants) significantly affected tobacco quality, yield, and budworm damage. Higher damage and lower yield and quality (grade) were observed in later-planted tobacco, on which peak tobacco budworm populations were higher but were present for fewer weeks during the season. Treatment thresholds of four or eight budworm larvae per 20 plants and the untreated control also resulted in significantly more damage and lower yields and grade, regardless of transplanting date. Damage due to the tobacco aphid, Myzus nicotianae Blackman, also was influenced by these two factors. More tobacco aphid damage was observed in late-planted tobacco and in plots treated when tobacco budworm densities were allowed to reach four or more larvae per 20 plants. Tobacco aphid damage was significantly correlated with tobacco budworm damage. Significant linear contrasts, and in some instances quadratic contrasts, were obtained among the budworm treatment levels for yield, quality, tobacco budworm damage, and tobacco aphid damage. Significant planting date X threshold level interactions were observed. Yield and leaf quality were not significantly different for treatment thresholds of either one or two budworms per 20 plants.