268 Peach-Growing 



Apparently, however, much can be accomplished in its 

 control by good orchard management. Rolfs makes it clear 

 that trees on which the foliage is thrifty and vigorous are 

 resistant in a high degree as compared with those that are 

 less well maintained. Roberts ^ also indicates that in 

 southern orchards trees maintained in a high state of cul- 

 tivation are commercially immune to this disease. 



Powdery-mildew (Sphcerotheca pannosa) 



This disease though widely disseminated is rarely of 

 serious economic importance. 



Course of development. 



Powdery-mildew develops usually in the early part of 

 the season, attacking the foliage near the ends of the branches, 

 the young tender twig growth, and sometimes the fruit. 

 The presence of the disease gives a white frosted appearance 

 to the affected parts. As only the young leaves and tips 

 are affected so far as the tree is involved, serious damage 

 rarely occurs. If the fruit is attacked when small, it is 

 likely to drop before it matures. It sometimes occurs 

 on trees in the nursery, causing the death of the young tender 

 growing tips of the twigs. This may prevent the trees 

 from developing into high-grade stock. 



Methods of control. 



But little attention has been given to the control of 

 powdery-mildew. Since it thrives best in warm, moist, 

 shaded locations, keeping the tops of the trees well pruned 

 so as to admit sunshine and air and thus promote the 



1 U. S. Dept. of Agr. BuU. 543. 



