PEACH DISEASES 315 



York State. In 1905 peach-mildew attracted attention in 

 Colorado, and in 1907 it was discovered in Nebraska and Utah. 



While peach-mildew is not everywhere destructive, it does 

 cause considerable damage at times. Twigs may be checked 

 in their growth or even killed; the foliage may be greatly 

 reduced in size and efficiency; and the future health of the 

 tree may be impaired. Seedlings are often badly affected, 

 and nursery stock suffers more than orchard trees. The last, 

 however, are not uncommonly affected, which, in case of 

 severe infection, may be entirely ruined for market. For- 

 tunately, not many trees in a given orchard are extensively 

 damaged. 



The susceptibility of varieties is not marked; this is true 

 at least for Colorado conditions. In Michigan, the popular 

 opinion prevails that only those varieties with serrate leaves 

 and lacking glands are affected with powdery-mildew. It 

 has been found by authorities, however, that this is not always 

 true. In Ohio, it has been observed that the Early Crawford 

 may be badly affected. At Geneva, New York, the disease 

 was found on but eight out of three hundred and fifty varieties : 

 Bailey, Conkling, Tillotson, Simmons No. 1, Wright, Morrell, 

 Thomas Rivers and Illinois Peach. In western New York, the 

 Crawford and especially the Denton are most susceptible. 



Symptoms. 



Injury is done by the mildew-pathogene to the leaves (Fig. 

 83), twigs (Fig. 83) and fruits (Fig. 84). Perhaps the fruits 

 are least affected of all. Along the lower surface of the foliage, 

 particularly at the midrib, are to be found abundant, irregular, 

 white blotches the mildew (Fig. 83) . It may also occur 

 on the upper surface. As a result of the affection the foliar 

 parts crumple and curl, the edges rolling toward and parallel 

 to the midrib (Fig. 83). Young leaves, when affected, fall 

 prematurely. Older leaves are dwarfed. Signs of the disease 

 may first be observed in early summer. 



