38 CALIFORNIA AGRICULTURAL EXTENSION SERVICE [CIRC 42

The Control of Peach Diseases—Peach diseases are usually controlled
 in one or more of the following ways: (1) by planting a variety
that is immune or resistant to the disease; (2) by planting a variety
only in the locality where the disease is not serious; and (3) by the
use of direct control measures, such as spraying or disinfection.?® The
quarantine service is a means of preventing the introduction and
spread of new diseases and insects within the state

Fig. 10.—Peach roots of young tree infected with erown call,

Crown Gall, Bacterium tumefaciens S. & T.—The bacterium caus
ing crown gall or root knot is found in many soils. Swellings or tumorlike
 enlargements are formed on the crown and the main roots and
sometimes on above ground parts of the tree (fig. 10). A tree affected
by this disease shows a loss of vigor, and may eventually die, The
trouble may be lessened by inspecting and rejecting diseased nursery
trees, and by care in cultivation so as not to wound the trees. Examine
the erown and main roots of stunted trees for evidences of the disease
20 Horne, W. T., E. O. Essig and W. B. Herms. Plant disease and pest control.
California Agr. Exp. Sta. Cir. 265:1-182. 1927.