1
Associate Professor, Department of Horticulture, University of Nebraska, Lincoln, NE 68583-0724. Journal Series no. 91-14 College of Agriculture and Natural Resources, Univ. of Nebraska.
2
Associate Professor, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow, ID 83843-4196. Journal Series no. 92712, Idaho Agricultural Experiment Station.
