Influence of plant age and genotype on resistance to European corn borer in sweet corn

Experiments were conducted to determine if the reaction of sweet corn (Zea mays L.) to European corn borer (Ostrinia nubilalis Hubner) was affected by plant age, genotype, or the interaction of plant age and genotype. Additionally, we wished to determine whether delayed larval development or exclusion of larvae was responsible for resistance. The experiments were conducted using a split plot design with six planting dates as main plots and three cultivars vith different maturation rates, 'GH1703', 'GH2690', and 'Prime Plus' (73, 78, and 85 day, respectively, Idaho standard) as sub-plots. Two distinct plant ages for each cultivar were concurrently infested with colony-reared neonatal European corn borer (ECB) larvae. plants were harvested after heat accumulation had reached 325-335 degree days (base 10C). Three to ten plants from each plot were destructively sampled. The number of larvae, number Of tunnels, and length of each tunnel were recorded to evaluate plant damage. The mass and developmental stage of each larva were recorded to determine if plant age or genotype affected larval development. There were significant interactions of plant age and cultivar affecting plant damage and larval number. in general, corn infested with ECB at V10-V12 stage (approximately 10-12 fully expanded leaves and palpable tassel development) sustained greater damage, more larvae, and greater larval development than did corn infested in the V6-V8 stage (6-8 fully expanded leaves). We conclude that ranking cultivars for resistance can be complicated by the interaction of genotype and plant age: resistance observed in corn infested in the V6-V8 stage was not apparent when infested in the V10-V12 stage. Exclusion or mortality of lan,ae appears to be a more important mechanism of resistance than does delayed larval development.