Manual of Gardening

The root-gall of raspberries, crown-gall of peaches, apples, and other
trees, is the most popularly recognized of this class of troubles (Fig.
216). It has long been known as a disease of nursery stock. Many states
have laws against the sale of trees showing this disease. Its cause was
unknown, until in 1907 Smith and Townsend, of the Bureau of Plant
Industry, United States Department of Agriculture, undertook an
investigation. They proved that it is a bacterial disease (caused by
_Bacterium tumefaciens_); but just how the bacteria gain entrance to the
root is not known. The same bacterium may cause galls on the stems of
other plants, as, for example, on certain of the daisies. The
"hairy-root" of apples, and certain galls that often appear on the

limbs of large apple-trees, are also known to be caused by this same
bacterium. The disease seems to be most serious and destructive on the
raspberry, particularly the Cuthbert variety. The best thing to be done
when the raspberry patch becomes infested is to root out the plants and
destroy them, planting a new patch with clean stock on land that has not
grown berries for some time. Notwithstanding the laws that have been
made against the distribution of root-gall from nurseries, the evidence
seems to show that it is not a serious disease of apples or peaches, at
least not in the northeastern United States. It is not determined how
far it may injure such trees.

Of obvious insect injuries, there are two general types,--those wrought
by insects that bite or chew their food, as the ordinary beetles and
worms, and those wrought by insects that puncture the surface of the
plant and derive their food by sucking the juices, as scale-insects and
plant-lice. The canker-worm (Fig. 217) is a notable example of the
former class; and many of these insects may be dispatched by the
application of poison to the parts that they eat. It is apparent,

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