PEACH DISEASES 



1555 



Fig. 2. Fruit Affected with the Fruit-Spot Stage of California Peach Blight. 



where the disease is abundant, forms one 

 of the most characteristic symptoms. 



The spots frequently develop into small 

 cankers which may girdle the twigs. 

 These may start on twigs of the current 

 year's growth, as shown in Fig. 1. Simi- 

 lar cankers are found associated with the 

 buds that have been killed. The twigs 

 and branches killed in this way are usu- 

 ally found first in the lower part of the 

 tree. The disease progresses upward and 

 in serious cases only the top branches of 

 the tree may be healthy. This mode of 

 progress of the disease may be related 

 to the fact that moisture Is held longer 

 in the lower branches of the tree and 

 hence the conditions for the development 

 of the disease are more favorable than 

 in the upper branches. 



On account of the fact that the one- 

 year wood in the peach develops the 

 fruit buds, it is seen that the form of the 

 disease above described is capable of 

 causing almost if not complete failure of 

 the crop. 



Constantly associated with the phase 

 of the disease on the twigs, is a char- 

 acteristic fruit spot and shot-hole effect 

 on the leaves. On the fruit, the spots 

 resemble the effect produced by the San 

 Jose scale. These are shown in Fig. 2. 

 The spots are at first rather small and 



purplish red. As the disease progresses 

 the spots become larger and a light- 

 colored area develops in the center. 

 Later the spots turn brown and where 

 abundant become confluent. On badly 

 affected peaches cracks may appear and 

 a more or less copious exudation of gum 

 may make its appearance. While inocu- 

 lation experiments have not yet been 

 carried out to prove that the spots on 

 the fruit and leaves are caused by the 

 same fungus as that which causes the 

 twig blight, it is highly probable that 

 such is the case. 



Cause 



Peach blight is caused by a parasitic 

 fungus known technically as Coryneum 

 heijerinckii. This fungus is known only 

 in the summer spore stage. A sexual 

 stage, if it exists, has not been certainly 

 associated with this disease. The fun- 

 gus, which is the initial cause of the 

 dying of the buds, and of the formation 

 of the spots and cankers on the twigs, 

 produces little three or four-celled brown 

 spores on the ends of threads from little 

 cushions which break through the outer 

 bark. These cushions are visible to the 

 unaided eye as black spots or pustules. 

 What is evidently the same fungus has 

 been found associated with the fruit spot 

 and shot-hole of the leaves. 



