NEW YORK EXPERIMENT STATION BULLETINS. 399 



When the spores begin growth they send a germinating thread from 

 each end. Under favorable conditions these threads grow quite rapidly 

 and the interlacing branches form a perfect mat of threads (mycelium). 

 When growing within the bark of the plum or cherry trees these threads 

 absorb their nourishment from the surrounding tissue and produce in 

 succession the swelling and rupture of the bark, the formation of summer 

 spores, the development of black-knot; and lastly, within the knot are 

 formed myriads of the winter spores. 



Both summer and winter spores are produced in great numbers, really 

 in incalculable numbers, and by their agency the disease assumes an 

 infectious character and spreads from tree to tree and from community to 

 community. The fungus is perennial and, having once gained lodgment 

 in a tree, continues to form new knots and to develop the succession of 

 summer and winter spores year after year. 



REMEDIES. 



Is it not plain, therefore, that the best way to deal with thoroughly 

 infested trees is to cut them down and burn them at once, thus insuring 

 the destruction of the spores before they spread the disease any further? 

 Trees not badly infested may be treated by cutting off affected branches 

 some distance below the knot. This operation is best performed in the 

 fall immediately after the foliage drops, because the winter spores are not 

 formed at that time and consequently there is less danger of their being 

 disseminated in the operation and also because the work can be done more 

 thoroughly when there are no leaves to hide the knot. 



The summer spores must also be taken care of in their season. As soon 

 as there are any indications of the formation of a new knot in the spring 

 or during the summer the branch on which it occurs should be cut and 

 burned. The first outbreak will probably be noticed about the middle of 

 May. 



It is important to note that if a branch containing the knot be cut from 

 the tree and thrown on the ground the spores will ripen in due time just 

 the same. Therefore, the practice of collecting carefully and burning 

 every knot can not be too strongly urged. 



The bulletins of the Massachusetts experiment station contain reports of 

 some experiments in the application of various substances for the purpose 

 of destroying the knot. Kerosene, turpentine, linseed oil, sulphate of 

 copper, and a mixture of red oxide of iron and linseed are mentioned as 

 among the substances tried. These seem to be effective in destroying 

 warts to which they are applied to saturation but care must be used with 

 the turpentine and kerosene or the entire branch will be killed. 



Concerted action on the part of all who are interested in growing plum 

 and cherry trees can do much toward eradicating black-knot. For those 

 cases that can not be reached by other means it would seem right that 

 proper legislative enactment be provided so that the fruitgrower may 

 protect his orchard from all infected trees of the vicinity. Let it be 

 remembered that in the work of thorough eradication of the disease the 

 wild plum and cherry trees before mentioned as host-plants of black- 

 knot must not be neglected. 



