1560 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



curled, and in severe cases tall prema- 

 turely. While usually the entire leaf is 

 affected, the mildew occurs also in spots 

 and then appears most abundantly upon 

 the under surface. 



Powdery mildew on the peach seems to 

 occur in two general conditions. The dis- 

 ease may be scattered on the fruit and 

 leaves, with a few twigs affected; this 

 may be referred to as the scattered form, 

 and is the most common condition of the 

 disease. Occasionally, however, trees are 

 found on which the disease is generally 

 distributed, when practically all the 

 twigs are attacked and the general growth 

 of the tree is seriously interfered with. 

 This may be referred to as the general- 

 ized form. See Fig. 2. 



In general the disease may be said to 

 be more abundant upon seedlings, though 

 the standard commercial varieties are not 

 uncommonly attacked. 



Cause 



Two mildews are reported upon the 

 peach, namely, Hpliaerotheca pannosa and 

 Podosphaera oxycanthae. It is possible 

 both of these diseases occur in the North- 

 west and that the scattered form is due 

 to the former species, while the more gen- 

 eralized form is due to the latter. The 

 species of powdery mildews are deter- 

 mined from the characteristics of the 

 perfect stage which develop late in the 

 season as small black bodies in the moldy 

 blotches on the twigs. This perfect stage 

 is seldom produced on the peach, and no 

 studies have been made to determine the 

 exact species occurring in the Northwest. 



Remedy 



Where occurring in the scattered form 

 on a few twigs and the fruit, the disease 

 can doubtless be held under control by 

 the methods described for the spring 

 treatment of California peach blight or 

 for the brown rot. Where the disease 

 attacks a tree in the generalized form, it 

 is very difficult to control, and ordinary 

 spraying methods, according to our ob- 

 servations, have not been successful. In 



• Hee circular Bulk-tin iri. Orecon Expiri 

 ment Statl'm. for the details or preparation 

 of this mixture. 



many cases such trees are found to be 

 seedlings and should be taken out. If 

 this condition occurs upon standard va- 

 rieties, severe cutting back followed by 

 thorough spraying should be tried as a 

 remedy. It is suggested that the grower 

 combine the recommendations given for 

 California peach blight in the fall and 

 for peach leaf curl and brown rot in the 

 spring. 



Crown Gall. See under Apple. 



MusuHOOM Root Rot. See under Apple. 



Pustular Spot 



Helminthosporiiim carpophilum Lev. 



Pustular spot of the peach is a disease 

 referable to a minute fungus, which is ap- 

 parently spread by spores that alight 

 upon the upper surface of the fruit, flour- 

 ish there and produce minute, light- 

 brown spots, often surrounded by an 

 angry red border. The red border is con- 

 spicuous in earlier varieties and is some- 

 times elevated and pustular in appear- 

 ance. This fungus greatly disfigures the 

 fruit and is very easily prevented. Three 

 applications of Bordeaux mixture have 

 reduced the amount of pustular spot to 

 less than one per cent; whereas un- 

 sprayed trees gave more than 16 per cent 

 of spotted fruit, much of which was se- 

 riously damaged. 



A. D. Selby 



Root Rot. See Apple Diseases. 

 Rot. See Broion Rot, this section. 

 Rosette. See "Yellows" this section. 



Bust 



Piiccinia pruni-spinosae 



H. S. Jackson 

 A true rust of the foliage of prunes is 

 not uncommon, though it is seldom pres- 

 ent in sufficient amount to he considered 

 serious. This disease is caused by a fun- 

 gus known technically as Ptiiccinia pruni- 

 spinosae. It is most abundant late in the 

 season and when serious may cause a 

 premature falling of the foliage. The dis- 

 ease is also known to attack the peach, 

 plum and other related trees. The dis- 

 ease may be recognized by the appearance 

 of small dusty brown or black sori on the 

 under surface of the leaves. On the upper 

 surface yellowish spots appear. It is 



