An Evaluation of Methods for Measuring Corn Earworm Injury12

Abstract

The magnitude of variance ratios obtained from analyses, when 3 corn earworm injury measurement scales (Centimeter, Survey, and Visual) were used on 5 sweet corn single crosses, indicated that under artificial infestation the Centimeter Scale based on depth of penetration gave the most precise measurements. Deviations from normal were found for the frequency distribution of inbred means obtained by a previously used measurement method (Injury Index). Tests for normality of the distribution of individual plants measured on the Centimeter Scale also indicated anormality. The anormalities occurred in both segregating and nonsegregating generations and appeared to be more closely associated with certain inbreds. Anormality of the Centimeter Scale was largely attributed to grouping in a single injury class all ears which had feeding on unfilled tips. A Revised Scale, which eliminates this discrepancy and generates frequency distributions in nonsegregating generations that are essentially normal, is proposed.