1. Western Regional Research Center, USDA, Agricultural Research Service, 800 Buchanan Street, Albany, CA 94710. The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.
2. Corresponding author. Phone: 510/559-5665. Fax: 510/559-5777. E-mail: tsk@pw.usda.gov