Evaluation and prediction of maize response to early-season injury from stalk borer

Davis, Paula
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The effects of stalk borer (Papaipema nebris (Guenee) (Lepidoptera: Noctuidae)) injury, imposed at corn-leaf stages 1 through 7, on visible injury, stalk elongation, and grain yield were evaluated in a three-year study. Tunneling by stalk borer in seven-leaf corn was confined to the lower nine internodes. A fifth-instar stalk borer that survives to pupation would be expected to produce a tunnel 15.8 cm long. Although tunneling shortens internodes at and above the tunnel, yield loss varied by year. A six-class scale was developed to evaluate injury. The average injury rating for a plot declined 0.332 ± 0.033 points per leaf stage. In years of adequate rainfall, yields declined linearly as plants were attacked later in development. Injury profiles were developed to describe feeding injury. Plot yield losses seem to be moderated by the ability of uninfested or slightly injured plants to compensate for severe stalk borer injury. Regression models were developed to predict plot yield and individual plant yield. Models for individual plant yield were combined with injury profiles to predict grain yield as a function of percentage of plants injured and corn development stage. Economic injury levels and economic thresholds were determined and a management program was presented. In a second study, degree-day models were used to time insecticide applications (permethrin) to egg hatch and larval movement. Although applications at egg hatch significantly reduced stalk borer density in grass terraces by 54-85%, applications timed with movement were more effective in reducing severe damage to corn. Finally, a management model, SBMGMT, was developed to simulate the stalk borer/corn agroecosystem. The model predicts stalk borer phenology, corn development, and grain yield for various management strategies.

Entomology, Statistics