282 CALIFORNIA FRUITS: HOW TO GROW THEM 



tions are practically free from.it. Some varieties are much more 

 subject to curl-leaf than others; generally speaking, some curl 

 nearly everywhere, others curl in one place and not in another, 

 others are practically free from curl in all situations. 



Curl-leaf occurs in various degrees. Mild cases do not seem 

 to injure either tree or fruit; severe cases destroy the fruit and 

 sometimes the tree itself. The disease is almost always at its 

 height when the young fruit is about the size of small peas. If the 

 curl is "bad," the fruit will fall to the ground, there not being 

 healthy leaves enough to afford the required support. If, however, 

 the curl is moderate and partial, only a part and sometimes none 

 of the fruit will be lost. The disease, as is well known, is of brief 

 duration, say twelve to twenty days,, after which the trees resume 

 a healthy appearance in every respect, and if the fruit has been 

 able to survive the ordeal, it also appears to grow and become as 

 perfect as if no check had been given to its growth. But it is 

 better to save the tree the burden of a new foliage growth. 



Mildew. This disease, which occurs in the form of whitish 

 felted patches on leaf and twig early in the spring, and finally 

 affects the fruit, has long been troublesome in this State, and 

 occurs on certain susceptible varieties in many localities from the 

 coast to the Sierra foot-hills. Observation in this State has fully 

 affirmed the statement of Downing, that the serrate, glandless- 

 leaved varieties are liable, and those with good glands on the leaf 

 stems are free. 



The conclusion would be that where mildew prevails, varieties 

 with serrate, glandless leaves should be avoided. But it has been 

 found that some glandless-leaved varieties, although subject to 

 mildew, resist curl-leaf. Therefore it may be worth while to com- 

 bat the mildew. This has been done effectually by treatment which 

 will be described in a later chapter. 



As with curl-leaf, mildew is prevalent some years and slight in 

 others. 



The most serious disease which has thus far stricken the peach 

 in California is locally known as the "peach blight," the work of 

 a shot-hole fungus (coryncuin). This also has been satisfactorily 

 checked by spraying as will be described in the Chapter on Dis- 

 eases of Trees and Vines. 



A common trouble of the peach known as "split-pit," has 

 recently been studied by the California Experiment Station and 

 the tentative conclusion has been reached that split-pits are physio- 

 logical phenomena and not caused by disease germ. Whether this 

 abnormal growth is due to weakness of variety or to cultural con- 

 ditions is not determined. It is true that varieties differ in amount 

 of splitting, and selection is being made to some extent on that 

 basis. 



