Abstract

Research was undertaken to determine the effect of time and rate of N sidedress application to corn (Zea mays L.) on the severity of northern leaf blight (NLB) caused by Exserohilum turcicum and grain yield loss (either associated with the disease or time of N application). Field experiments were conducted at two locations in Pennsylvania (Lancaster and Centre Counties) during 1985 and 1986. Twenty-four treatment combinations were examined: An NLB resistant and an NLB susceptible hybrid; an E. turcicum inoculated and an unioculated, fungicide-treated control; two split applications of N (10 lb/acre at planting followed by 140 lb/acre as a sidedress, and 50 lb/acre followed by 100 lb/acre as a sidedress); and three sidedress application times (5, 7, and 9 wk after emergence, corresponding approximately to the 8-, 10- and 12-leaf stages, respectively). Northern leaf blight reduced yields in susceptible hybrids up to 35%. Neither N split application rate, sidedress application time, nor the interaction of the two factors significantly affected NLB development. However, grain yield and other variables decreased significantly when the sidedress application of the 10/140 lb N/acre rate combination was delayed until 9 wk after emergence. Time of sidedress application did not affect yield when the 50/100 lb N/acre rate combination was used. Thus, the study demonstrated that when a major portion (approximately 95%) of the N requirement for the crop is applied as a sidedress, it is best to apply the N prior to 9 wk after emergence (12-leaf stage). Time of sidedressing is not as critical when a smaller portion of the N requirement for the crop is to be applied as a sidedress (approximately 66% of the N sidedressed). It is clear from this study that presidedress N rates are crucial in determining the optimum time for sidedress applications. In addition, with grain yield losses of up to 35% on the NLB susceptible hybrids, the need for growing resistant hybrids is underscored.

Copyright © 1990. . Copyright © 1990 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, 5585 Guilford Rd., Madison, WI 53711 USA