The following article is the twelfth annual report of progress in studies on orchard frost protection published in California Agriculture.

Rodney Vertrees provided the test peach orchards and the under-tree wind machine, and assisted in the tests.

Fred Lory and Richard Miller, Department of Agricultural Engineering, University of California, Davis, assisted in these studies, as did George Post, Dave Chaney, and Dave Ramos, Farm Advisors, University of California, Sutter County.

Joe Ganser and Tom Beecroft, United States Weather Bureau, also assisted with forecasts and participation in the spring tests.

The return stack orchard heaters used in the experiment were loaned by National-Riverside Company and Scheu Products Company.

The above progress report is based on Research Project No. 400-U.