Tower mounted wind machines raise orchard temperatures largely by the forced mixing of cold orchard air with the warmer air overhead. However, tests in an almond orchard in the Chico area –in 1955 and 1957–showed that the air jet from tower mounted machines had difficulty in penetrating the tree canopy –typical of deciduous orchards–formed by the intertwining of branches of adjacent trees. Underneath the tree canopy deciduous orchards are relatively open but growers report that most frost damage occurs in the lower part of the trees.

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

Rodney Vertrees provided the test peach orchard and the under-tree wind machine and assisted on test nights.

C. E. Barbee, Fred Lory, and Richard Miller of the Department of Agricultural Engineering, University of California, Davis, assisted in these studies.

Joe Ganser and Tom Beecroft, United States Weather Bureau, also assisted with forecasts and participation in the tests of March 20 and 25.