1. Department of Agricultural and Resource Economics, University of Tennessee, 2521 Morgan Circle, 321C Morgan Hall, Knoxville, TN 37996, USA
2. Department of Horticulture and Landscape Architecture and Department of Agricultural Economics, Purdue University, West Lafayette, IN 47907, USA
3. Department of Horticulture, Michigan State University, 1066 Bogue Street, East Lansing, MI 48824, USA
4. Department of Plant and Soil Sciences, University of Delaware, 146 Townsend Hall, Newark, DE 19716, USA