1. Geophysical Inst., Univ. of Alaska Fairbanks AK99775
2. School of Natural Resources, Univ. of Nebraska Lincoln NE 68583‐0728
3. Dep. of Plant Pathology Univ. of Nebraska Lincoln NE68583‐0722
4. Dep. of Agronomy and Horticulture Univ. of Nebraska Lincoln NE685893‐0724