75 



used at the proper time, will, to a large degree, prevent the ravages of the 

 fungus. From past experience it is thought doubtful that a third applica- 

 tion does sufficient good to make it worth tr.ving. The onl.v spra.v to be 

 recommended at this writing is a properly prepared Bordeaux mixtnre of 

 6-4-50 formula. Further experiments ma.v show that a weaker Bordeaux 

 can be used with good results — that point has not .vet been determined. — 

 Washington Experi menial Station Bulletin Xo. (?}. 



Bl.\ckspot Canker. 



{Macruphomn ciin ispora, C. H. Peck; Glovosporium malirorticis, 



A. B. CORDLEY.) 



Common Xa)nc of the Disease. 

 Blackspot canker is known under a number of different names. Canker, 

 Black canker, Blackspot Apple canker, Blackspot, Dead spot Apple tree 

 Anthraenose and Sour Sap disease, are several of the names applied to it. 

 There are several somewhat similar diseases of the apple throughout the 

 Tnited States. Among these are the Xew York Apple tree canker and the 

 Illinois Apple tree canker. The term canker is a general one that includes 

 nearl.v all the diseases involving the bark of trees. In order to retain 

 uniforniit.v of names and to retain the name which so accurately describes the 

 canker, the author has chosen to use the common name of Blackspot canker. 

 Oceniiiny on both Fruit and Bnrlc. 



Parasitic in the bark and sapwood of the trunk and the branches and on 

 the stored fruit of the cultivated apple. 



In the Bark. — Infested areas depressed, dark brown to blackish, oblong 

 in outline one-fourth to si-x iuelies in lengtli or longer; sometimes merging 

 together when fully grown, free from the sapwood and bounded by a ragged 

 fissure. 



On the Fruit. — Decaying spots light to dark brown, concave, dry and 

 leathery; acervuli numerous, usually larger than those in Dark, usually con- 

 centrically arranged. 



Cause of the Disease. 



Numerous theories have been offered in explanation for the occurrence 

 of the disease. Nearly all these theories have been abandoned. One which 

 has been recently promulgated is the sour sap theory. This holds that the 

 trees have been feeding on an excess of nitrates ; that nitrates collect in the 

 liark of the tree; that fermentation takes place and puts the bark in such a 

 condition that the fungus is able to penetrate it. Such a theory is easily 

 refuted by testing the bark for nitrates. Such tests have been made of 

 infested bark in all stages and of healthy bark, and in neither case have 

 nitrates been found. 



It has been known and definitely proven for a period of several years 

 that the canker is caused by a parasitic fungus. According to Minto (1), 

 Pierce as early as June, 1S95, grew the fungus from diseased bark collected 

 at Olympia, Washington, inoculated healthy trees in the Sacramento Valley, 



