PLUM DISEASES 
361 
January to June, depending upon the locality, and which are 
discharged upon maturity. 
is similar to that of the summer 
spores previously described ; they 
propagate the parasite. The 
original portion of the knot is 
thus matured, but the fungus in 
the bark may continue to grow 
at either end, thereby increasing 
the length of the old knot. In 
this manner a single knot may 
in time extend a long distance 
on a branch, its course tending to 
proceed spirally about the stem. 
The further history of these spores 
Fig. 103.— Black-knot; cross- 
section of a knotted twig. The 
enlargement has not completely en- 
circled the twig. 
Control. 
Eradication of the causal fungus is the recognized method of 
most practical value in the control of black-knot. In following 
Fig. 104. — Black-knot ;  cross- 
section of a diseased twig. The 
knot has completely encircled the 
twig. 
species of plums and cherries. 
this principle, it should be 
remembered that (1) the sum- 
mer spores are produced abun- 
dantly during the late spring 
and early summer, (2) the 
winter spores develop from 
midwinter to spring, and (3) 
there are many kinds of plums 
and cherries attacked by these 
spores. Therefore, prune out 
the knots before either kind of 
spores is matured, that is, in 
the fall or early winter, before 
January. Look for them in the 
wild as well as in the cultivated 
An annual fall inspection of the 
trees and the removal and destruction of all the knots is the most 
