278 Bulletin 276. 



Pierce ('00) collected a great amount of data on the geographical 

 distribution of this disease. This is set forth in detail in the bulletin 

 as indicated at the bottom of this page. Like many other fungous 

 diseases it is of an epidemic nature, appearing with severity in any 

 locality more or less regularly every four or five years. The epidemic 

 periods of this disease in New York since 1893 appear from the records 

 (Duggar 'og, Orton '03, '04, '08, '09) to have been 1893, 1897-8, 1902-3, 

 1907-8. The direct correlation of these epidemics with certain weather 

 conditions will be brought out later. 



Economic importance. — The character of the injury from this disease 

 is such as to render very difficult if not impossible an accurate estimate 

 of the losses resulting from its ravages. In attempting to determine 

 accurately such losses we are confronted with a number of difficulties. 

 It cannot be computed from the evident effects during the season in 

 which the attack occurs, since a severe attack of the disease may greatly 

 reduce or prevent entirely the setting of fruit buds for the following 

 season. Moreover the late growth of the shoots induced by the attempt 

 to replace the leaves lost by the Curl early in the season often results 

 in a failure of the wood to mature. Serious winter injury is likely to 

 follow with the loss of the ends of the limbs or even of the entire tree. 

 Then, too, the direct effects of the disease during the season in which 

 it has appeared will vary greatly with conditions. The defoliation of 

 the trees which follows as a result 01 the dying of the curled leaves, may 

 be so complete as to cause the dropping of the fruit which has already 

 set (Fig. 84). In other cases the trees may be in such good condition 

 from proper cultivation, etc., as to be able to come through the attack 

 with sufficient healthy foliage to hold and mature a part or all of the 

 fruit crop. The effect of the disease upon the fruit crop and upon the 

 vitality of the tree appears to depend not only upon the extent and 

 severity of the attack but also upon the condition of the tree as deter- 

 mined by its vigor, location, and the character of the succeeding winter. 

 Pierce ('00) made a very careful and extensive study of this phase of 

 the subject and concluded that the average annual loss from Peach 

 Leaf Curl in the United States could not be less than $3,000,000. The 

 very general practice of spraying for this disease in most peach sections 



'00. Pierce, N. B., Peach Leaf Curl; Its Nature and Treatment, U. S. . A., 

 Div. Veg. Phys. and Path., Bui. 20:12-19, 1900. 



•03, '04, '08, '09. Orton, W. A., Plant Diseases in the U. S. U. S. D. A., Year 

 Book for 1902:716; Year Book for 1903:550; Year Book for 1907:579; Year Book 

 for 1908:535. 



'00. Pierce, N. B., Peach Leaf Curl; Its Nature and Treatment, U. S. D. A., 

 Div. Veg. Phys. and Path., Bui. 20:19-21, 1900. 



