Influence of Seeding Rate, Nitrogen Management, and Micronutrient Blend Applications on Pith Expression in Solid-Stemmed Spring Wheat

The wheat stem sawfly (Cephus cinctus Norton [Hymenoptera: Cephidae]) is a serious threat to wheat (Triticum aestivum L.) and other cereal grains in the northern Great Plains. Wheat cultivars with high expression of pith in the culm of the stem (stem solidity) can minimize losses associated with sawfly infestations and subsequent stem boring of the larva. Based on the widespread area now sown to solid-stemmed wheat, our objective was to develop an integrated nutrient and planting strategy specific to solid-stemmed spring wheat using modern farming techniques. Five levels of banded N fertilizer (0, 30, 60, 90, and 120 kg N ha(-1)) were arranged in a factorial combination with three levels of sowing density (100, 300, and 500 seeds m(-2)) and grown at three sites in southern Alberta, Canada, from 2007 to 2009. Increased planting densities optimized yield, but an inverse relationship with pith expression (stem solidness) was observed. Low plant populations (100 seeds m(-2)) were often most effective at maximizing pith expression in solid-stemmed wheat and reducing sawfly cutting damage. However, this usually required the highest rates of N fertilizer, so a system of low seeding rates and high N may not be economical based on fertilizer input costs and the generally lower grain yield response (-9%). An integrated planting and nutrient strategy for solid-stemmed spring wheat cultivars consists of seeding rates no greater than 300 seeds m(-2) and basal N applications in the range of 30 to 60 kg N ha(-1).