EXPERIMENT STATION BULLETINS. 263 



It will be seen that the fruitgrowers of any section have it in their 

 power to secure the prompt destruction of all fruit and trees in which the 

 disease appears. In Berrien, Van Buren, and Allegan counties there are 

 numberless cases where the disease has been kept in check, even after it 

 has appeared in an orchard, and one can also find in those same counties 

 other instances in which the law has not been enforced, where yellows 

 appeared in fully 30 per cent, of the trees in 1893, and even then nothing 

 was done beyond cutting off the branches and leaving them on the ground 

 to scatter their contagion, while the trunks of the trees left standing 

 sprouted and sent up wiry shoots that show unmistakable signs of yel- 

 lows. If the owners alone are to be the sufferers, after all that has been 

 said and written on the subject, one would hardly waste a thought upon it, 

 but one can not help feeling sorry for the neighbors whose orchards seem 

 doomed to destruction, even though they have not shown public spirit 

 enough (to say nothing of their private interests) to secure the enforce- 

 ment of the law. As will be noticed, the law also provides for the destruc- 

 tion of the "black knots," upon plum trees, which is a disease fully as 

 fatal as peach yellows, where its appearance is not guarded against. With 

 a little concerted eff'ort, however, this disease also can be readily controlled. 



BLACK KNOT. { Ploivrightia morbosa. Sacc.) 



In some parts of the state entire plum orchards have been destroyed by 

 this disease, and there is great danger of its obtaining a strong foothold 

 in the plum-growing districts and crippling that thriving industry. The 

 only hope of safety is in the thorough awakening of every plum-grower to 

 the danger that menaces him. If they could see the thousands of acres of 

 plum orchards that have been blotted out by this disease in the state of 

 New York, during the last five years, they might be upon their guard. 



In order to successfully combat this disease, all the plum-growers in a 

 given locality must be leagued in an intelligent warfare asrainst it. If one 

 man allows the knots to form upon his trees he will spread the disease to 

 his neighbor's orchards. As much of the danger comes from the disper- 

 sion of the spores, formed by the knots before they have taken on the black, 

 pimply appearance (Fig. 9, 1) that is usually regarded as distinctive, every 

 one should be familiar with the changes through which the knots pass. The 

 spores (seeds) are borne through the air and, falling upon the branch of a 

 plum tree, soon germinate and penetrate the tissues. They grow there 

 until the following spring without manifesting their presence. A swell- 

 ing will then be seen at the point infected, generally two or three inches 

 long; the bark cracks and the branch seems to puff out to twice its normal 

 size. If these incipient knots are cut off and burned at this time, the 

 injury to the tree will be stopped and, what is of most importance, it will 

 be destroyed before it has had time to ripen and scatter its spores. In one 

 or two months, if left upon the tree, the knot becomes covered with an 

 olive-green mold, made up of an immense number of spores upon their 

 supporting stalks; these are soon scattered by the wind and disseminate 

 the disease. In the autumn, a hard, black crust forms over the knot; this 

 is covered with minute pimples in which a second form of spores is pro- 

 duced. They ripen late in the winter and are the source of other knots. 

 Hundreds of knots often appear upon a single tree, and as they not only 

 rob the tree of food, but practically strangle and starve the branches upon 

 which they are located, by girdling them and thus shutting off the supply 

 of food, the tree is soon destroyed. 



