Grain Yield Reduction Caused by Second Generation European Corn Borer in BS9 Corn Synthetic1

Abstract

Damage to the corn (Zea mays L.) plant caused by the European corn borer (ECB) [Ostrinia nubilalis (Hübner)] can cause substantial grain yield reduction. The ECB damage results in both physiological reduction, caused by decreases in plant productivity, and harvest loss, caused by weakening of the stalk and shank from tunneling by the fifth instar larvae (borers). Yield reductions caused by ECB can be decreased with the use of resistant hybrids. Iowa normally has two generations of ECB per year, and resistance to the two generations is expressed by separate genetic mechanisms. A corn synthetic, designated BS9, was specifically developed and selected for resistance throughout the life of the plant. This study used hand and machine‐harvested plots of a control treatment and a treatment of a high infestation of second generation ECB to estimate the magnitude of physiological reduction and harvest loss contributing to a decrease in total grain yield. Corn cultivars used were the original and fourth cycle populations of BS9 [BSSCO and BS9(CB)C4], the two populations crossed with four inbred line testers, and two check single‐cross hybrids. Physiological reduction and harvest loss were estimated to be 25.9 and 2.8%, respectively. Harvest loss had little effect on total yield reduction, and contributions by other genetic factors seemed more important than ECB damage on harvest loss. Ear drop page under high insect pressure was determined more by the inherent properties of the hybrids for ear retention than as resistance to ECB. Whereas ear droppage before harvest had little effect, stalk lodging was significantly correlated with harvest loss.