264 



STATE HORTICULTURAL SOCIETY. 



One source of contagion is through nursery stock, and young orchards 

 should be carefully watched, when trees are obtained from infected dis- 

 tricts. Not only is there danger from 

 knots upon other plum trees, but it 

 seems probable that the knots upon 

 the cultivated cherries, choke and 

 other wild cherries, and wild Ameri- 

 can and other wild plums, may be of 

 the same species and be able to com- 

 municate the disease to plum trees 

 in our orchards. Experiments by 

 inoculation would seem to indicate 

 that the knots upon choke cherries 

 will communicate the disease to cul- 

 tivated plums, and the only thing 

 that points to the contrary is that 

 the plum orchards in Oceana county 

 are sometimes surrounded by thick- 

 ets of the wild pin cherry {Primus 

 Pennsylvanica L. ), and yet remain 

 free from disease. However, as these 

 thickets of wild plums and cherries 

 are at best a nuisance, prudence 

 would indicate the desirability of 

 applying the ax and fire to them, 

 as there may be conditions under 

 which the disease may be transmit- 

 ted. It has been noticed that there 

 are unknown conditions under 

 which the disease has greatly in- 

 creased virulence. For several years *^3i^^p^^lf= 

 it may make but little headway, but Ot^^ff^- 

 at length a time will come when it ^^^=^ 

 will sweep like fire throuah ihe 



7 I J J J.- 'i -LI X Fig. 9. Black Knot. Plowriphtiu vwrbosa. Sacc. 



plum orchards and entirely blot l. stem of pJum tree with knot upon it, as it appears 



them out '^ *^® '^^'^ ^^^ winter. 



.' . . . 2. Perithecium with mycelium, a a between the cells 



Ihe disease is certainly getting a of stem, and covered with filaments bearing spores. 

 i> +1 1 I -I-.^ ^^-.^^ „,^^.^iJZ,^ 6, at^their extremities. Section made in May. 



strong 



spores {conidia}, more highly 

 a cavity containing stylospores. 



m some sections, 3. FUaments and 



and it behooves every plum-grower, "J^Son through 

 even if he has but a single tree, to After Fariow. 

 be upon the alert. 



It is now nearly five years since the writer began a crusade against the 

 disease, and, from the reports that come in, it is encouraging to see that 

 the growers appreciate the danger that menaces them, and are acquiring 

 the knowledge of its appearance necessary to enable them to combat it 

 upon its manifestation. What is needed now is a united public sentiment 

 against it that will secure prompt action upon the part of all. 



While the destruction of the outside sources of contagion should not be 

 neglected, it seems desirous that the trees should be kept in such a condi- 

 tion as will enable them to withstand the disease; hence, thorough cultivation 

 and liberal quantities of mineral manure should be given the orchards. As 

 severe outbreaks of the disease often follow years of full crops of fruit, it 



