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. Additio nally, we wished to determine whether delayed larval development or exclusi on 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 P lus' (73, 78, and 85 day, respectively, Idaho standard) as sub-plots. Two d istinct plant ages for each cultivar were concurrently infested with colony -reared neonatal European corn borer (ECB) larvae. plants were harvested af ter 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 pla nt 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 pla nt damage and larval number. in general, corn infested with ECB at V10-V12 stage (approximately 10-12 fully expanded leaves and palpable tassel develo pment) sustained greater damage, more larvae, and greater larval developmen t 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 i nteraction 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. Exc lusion or mortality of lan,ae appears to be a more important mechanism of r esistance than does delayed larval development.