Yield Response of Corn Stands to Stalk Borer (Lepidoptera: Noctuidae) Injury Imposed During Early Development

Abstract

In a 3-yr study, visual injury and grain yield were evaluated for two fullseason corn ( Zea mays L.) hybrids infested by stalk borer larvae, Papaipema nebris (Guenee), at leaf stages 1 through 7. Individual plants were assigned a rating based upon a six-class scale, and the average rating per plot was determined; 80% of the total number of injured plants within each plot were classified as injured within 1 wk after infestation. A significant linear relationship between leaf stage and injury rating was detected in all years of the study, with injury rating declining at an average rate of 0.332 ± 0.033 points per leaf stage. In all years, infested plots yielded significantly less grain than uninfested control plots. Average yields of Pioneer hybrids 3541 and 3377 were reduced by 24.8 and 18.9%, respectively, when compared with uninfested control plots. In 2 of 3 yr, yield losses declined linearly as plants were attacked later in development. However, in a drought-stressed year, leaf stage was independent of plot yield even though injury ratings for each leaf stage were very similar to those recorded during years with normal rainfall. Linear models, which regressed injury rating on yield, were developed and compared for each year and hybrid combination.