SOME OF Oru MOST COMMON APPLE DISEASES 867 



Little is being done by pathologists or growers in this state 

 toward the control of the disease. In the light of the above 

 theories, all of which agree that the trouble is a result of some 

 Irregularity in the water supply, it appears that any operations 

 which will tend to make uniform the water relations of the soil 

 and of the plant will aid in reducing the disease. Some points 

 worthy of note in this connection are soil drainage, proper tillage, 

 and cover cropping at the proper season. It is also advised that 

 pruning and thinning be not overdone. Wherever the trouble 

 occurs periodically in storage, it is recommended that the store- 

 room be not too dry and that the temperature be kept at about 

 30 to 32 degrees Fahrenheit, 



EUROPEAN APPLE-TREE CANKER 



This canker is caused by the fungus Nectria galligena. In the 

 younger stages it is not easily recognized as distinct from any other 

 canker. As new callus is developed around the margin of the 

 wound, it is attacked and killed by the fungus; the latter spreads 

 for a short distance, where another layer of new growth, or callus, 

 is formed. This process is repeated until a series of ridges or 

 rolls of callus may be developed, giving the appearance so charac- 

 teristic of this disease in its later stages. The trouble seems to 

 be on the increase in New York. For its control it seems reason- 

 able to conclude that the measures advised in the case of the New 

 York apple tree canker are applicable. (See Black Eot. Leaf 

 Spot, and Canker of Apple, page 861.) 



ILLINOIS BLISTER CANKER 



This disease is caused by the fungus Nummularia discreta. 

 The blister canker is chiefly a disease of apple orchards of Indiana, 

 Illinois, and neighboring states, although it is now present 

 in this state. It is usually found on the larger limbs and the 

 trunks, affecting the bark and wood. The diseased bark is at first 

 brown and slightly sunken, showing healthy bits of tissues scat- 

 tered within the generally diseased area. In a later stage the bark 

 becomes much roughened and blackened, and falls off in irregular 

 patches, exposing the wood. On the dead areas, or even on the 

 bark before it falls away, the fruiting parts of the fungus are devel- 

 oped. These bodies are relatively large and black, and therefore 



