PEACH DISEASES 



1557 



years ago, but no steps were taken to 

 investigate it. It has now become very 

 serious and is under investigation. 



H. T. Gussow, 

 Ottawa. Canada. 



Crown Gall. See Apple Diseases. 



Peosty Mildew. See Leaf Spot, tliis 

 section. 



Gdm Flow. See Blight, this section. 



Griijiosis. See Blight, this section. 



Juno Drop 



June Drop is often named by peacli 

 growers as a specific trouble. It con- 

 sists in the dropping of tlie young 

 peaches during the month of June, 

 though dropping sometimes comes 

 earlier. The cause seems to be physio- 

 logical and need not be feared where the 

 trees have been prevented from over- 

 bearing, or protected from the effects 

 of drought by thorough cultivation the 

 previous season. See Setting and Drop- 

 ping OF Fruits, under Fruits. 



Little Peach. See Yellows, this sec- 

 tion. 



Leaf Curl 



Exoascus deformans 



H. S. Jackson 



The most common and destructive dis- 

 ease of the peach in the humid sections 

 of the Northwest, and probably wherever 

 the peach is grown in that region, is 

 without doubt the peach leaf curl or 

 "curl leaf," as it is most commonly 

 known among growers. 



Symptoms 



The disease may be recognized by the 

 characteristic effect upon the foliage and 

 twigs. The leaves are peculiarly and 

 characteristically curled as shown in 

 Fig. 1. This curling results from a stim- 

 ulation induced by a parasitic fungus, 

 which grows among the cells of the leaf. 

 The infected leaves become considerably 

 increased in thickness and breadth. The 

 cells of the tissues develop thickened 

 walls and increase in size and number. 

 The tissues of the midrib do not increase 

 to any extent and the abnormal growth 

 in the tissues on either side, as de- 

 scribed above, results in a puckering or 

 curling. Since the greatest growth is 

 in the tissues toward the upper side. 



there is a tendency for tlie upper surface 

 of the curled leaf to be convex. Affected 

 twigs are increased in thickness and very 

 much shortened. The green coloring 

 matter normally present in healthy twigb 

 is bleached out so that diseased twigs 

 appear whitish. 



Cause 

 The parasitic fungus causing the 

 trouble is known as Exoascus deform- 

 ans. The vegetative condition of the fun- 

 gus (the mycelium) is present among 

 the cells of all diseased tissues and ab- 

 sorbs the juices needed for the proper 

 growth of the tree, thus stimulating the 

 tissues to produce the abnormal struc- 

 tures described above that are not able 

 to properly perform the functions of nor- 

 mal tissues. Reproductive bodies or 

 spores are produced in little sacs which 

 form a layer on the surface of affected 

 leaves. These form under the cuticle, 

 finally pushing it off and imparting to 

 the surface a frosted appearance. In 

 each sac are borne at first eight spores. 

 These become greatly increased in num- 

 ber by budding within the .sac. The 

 spores thus formed escape by the rup- 

 ture of the sac. These spores, which are 

 presumably carried over the winter on 

 the surface of twigs and bud scales, pro- 

 duce infection as soon as the leaf buds 

 open in spring. 



Affected foliage usually' drops, and, 

 where abundant, may cause more or 

 less complete defoliation of the tree. 

 Such trees set little or no fruit. Defol- 

 iated trees usually leaf out again, so tliat 

 in midsummer little sign of the disease 

 may be found. The effect of such de- 

 foliation, however, is to stunt the tree. 

 Trees allowed to become infected year 

 after year are usually unprofitable. 



Besides the method mentioned above, 

 the fungus may be carried over from one 

 season to the next by the mycelium liv- 

 ing over the winter in the twigs. The 

 fungus probably gains entrance to the 

 twigs by the growth of the mycelium 

 down the leaf stalks of affected leaves 

 into the twig. Where such twigs remain 

 alive over the winter the leaves produced 

 in the buds on these twigs will always 



