Corn stalk response to plant population and the Bt-European corn borer trait

Current research indicates that plant populations should increase above the current Wisconsin recommendation of 74100 plants ha(-1) for higher corn (Zea mays L.) grain yields. However, stalk lodging is a major constraint to increasing plant populations. One option growers have is using Bt (Bacillus thuringiensis) hybrids, which are known to lodge less. A new method for assessing stalk lodging risk is needed. The objectives of this study were to (i) assess rind strength of corn hybrids with or without the Bt trait to increasing plant populations at natural levels of European Corn Borer [ECB, Ostrinia nubilalis (Hubner)], and (ii) determine the potential of rind strength measurements for predicting stalk lodging. In 2003 and 2004, rind penetrometer resistance (RPR) was used to measure rind strength for four Bt and five non-Bt hybrids with plant populations ranging from 64220 to 123500 plants ha(-1) at 10 locations in Wisconsin. Stalk lodging increased from 6 to 18% as plant population increased, and only at one location, Arlington, did Bt hybrids lodge significantly less (20 vs. 42%) than non-Bt hybrids. The RPR of both Bt and non-Bt hybrids decreased from 3.9 to 3.7 load-kg plant(-1) with increasing plant population. Plants with rind strength measurements < 3.9 load-kg plant(-1) taken at physiological maturity showed more lodging. Thus, such measurements appear to be a good indicator of stalk lodging potential in a high plant population situation. This new method has potential to help growers prepare for grain harvest by identifying fields with plants having average RPR below a 3.9 load-kg plant(-1) threshold, and adjusting harvest schedules of suspect fields earlier to avoid yield losses caused by stalk lodging. Further research using more hybrids across a range of environmental conditions and plant populations will be necessary to fully understand the importance of this tool and its potential importance in understanding and identifying high lodging potential environments.