125 



It is best known and most destructive as a pear disease, but is also 

 common and wide-spread in the apple orchard. It alTects likewise 

 the quince, the mountain-ash, the raspberry, the blackberry, and 

 some other rosaceous plants. 



Its characteristic symptom is a sudden dying- and blackening- 

 of the newer growth of twigs and leaves, beginning generally at 

 or near the tips and thence extending downward. The dead twigs 

 and leaves presently become almost inky black, and remain con- 

 spicuous among- the green and healthy leaves during much of the 

 growing season. The disease extends rapidly at times, especially 

 in the pear, but sometimes more slowly. Insects assist in its dis- 

 semination, especially when the trees are in bloom. Its bacterial 

 germ remains dormant over winter in some of the affected trees, 

 and starts again the following spring. It is mainly an orchard 

 disease, but occurs occasionally in nurseries, particularly where 

 these grow adjacent to affected orchards. If it appears in the nur- 

 sery infected trees should be promptly cut out and destroyed, as no 

 fungicide or other artificial treatment will serve to check its 

 progress. 



Thk Bi.ack-knot. 



This is a fungous disease of the branches of plum- and cherry- 

 trees, appearing first in the form of a thickening or swelling of 

 the twig, which becomes thicker on one side than on the other, and 

 here the distended bark presently breaks and a spongy mass grows 

 out. This generally develops into large sooty-black wart-like 

 growths, with slightly granular surface broken by deep fissures 

 runningmostly crosswise of themass (Fig. 14). The fungus parasite 

 causing this disease is technically known as PhKcrio-Jilia niorhosa. 

 " Since the knot generally occupies only one side of the limb, 

 it does not entirely check the life processes, and the limb beyond 



conti n u es to 

 grow and put 

 forth leaves. It 

 is only where 

 the knot e x- 

 I'Il;. 14. Ihf. 1>lack-knot. ((.larman.) tends com- 



pletely around the twig or branch that the part beyond is killed at 

 once. When the knots are abundant trees maybe killed in a couple 

 of year, and indeed whole orchards may in the course of a few 

 years become so infested as to be worthless, although the injured 

 trees may survive in a feeble way for a longer period." 



*H. Garman, Kentucky Bulletin No. 80. 



