8 Strate Crop Pest COMMISSION OF 
: CroWN GALL AND Hairy Roor DISEASES. 
Almost all orchardists are familiar with the appearance of 
the disease known as crown gall or root knot. This is not caused 
by an insect, but is a plant disease. Plants affected with the 
hairy root disease send out at the crown a tremendous number 
of fibrous roots, which are distinctly noticeable as soon as the 
tiee is dug. Plants affected with the true crown gall form a 
large knot right at the crown, which may vary, according to the 
size of the tree and stage of the disease, from an inch or so in 
diameter to a knot twice the circumference of the tree, or more. 
Nurserymen are prevented from sending out trees infected with 
this disease in the same manner as they are prevented from send- 
ing out trees infested with nematodes or woolly aphis. Any 
stock sent out infected with crown gall, nematode root knot or 
woolly aphis is subject to confiscation. 
Buack Knot. 
This is a disease on plum and cherry trees, which manifests 
itself by large knots upon the limbs, which knots increase in 
size year to year, gradually sapping the vitality of the tree. 
These knots are caused by a fungus. When trees affected with 
black knot are found in a nursery, all knots are required cut 
out before a certificate of inspection is granted. 
CONCLUSION, 
The above are the principal insects at present most injurious 
to nursery stock. As time goes on it is not impossible that other 
insects, at present unknown, may ultimately become more injuri- 
ous than any of these. Conditions are constantly changing, and 
with the wholesale destruction of forests and birds—two very 
important factors in the control of insects—it is not surprising 
that insects have assumed the importance which they now have. 
in every state and country scientists are now working on the 
