215 



This disease is now so universally known that no description of it 

 should be necessary. An enumeration of its various names, such as 

 blight, pear-blight, fire-blight, blossom-blight, blight-canker, spur-blight, 

 etc., will serve as an identification of the disease even to the inexperienced 

 orchardist. 



As the various names imply, pear blight attacks leaves, twigs, flowers, 

 fruit, and even large branches and trunks. One reason for its extremely 

 serious effects upon the pear tree is its ability to cause trunk-cankers 

 which girdle trees and result in their death. 



Losses from pear blight are great — so great that to term this dis- 

 ease the one limiting factor in the growing of pears in Illinois is not an 

 exaggeration. Losses result annually in crop reductions, but the injury 

 to trees is often so severe that its efifects impair the quantity of the crop 

 through many subsequent seasons. Anderson* estimates that losses from 

 blight average annually in the United States 25 per cent of the potential 

 bearing power of the trees. Pickett" places the loss from this disease 

 on the fruits mentioned at $5()0,()(1() for 1 county and at $1,500,000 for 

 the entire state, and reports that southern Illinois is more aflfected than 

 northern. 



Estimates of crop reductions caused by this disease in Illinois in 



1922 and 1!)23 are shown in Table 37. In the former year the reduction 

 of 5 per cent was equivalent to 26,800 bushels valued at $2G,800, and in 



1923 the crop reduction of G per cent was equivalent to 19,000 bushels 

 valued at $i:,S()0. 



The distribution of pear blight in Illinois is shown on Map 55. It 

 occurs from the northern to the southern and from the eastern to the 

 western boundaries of the state and is known in all but 27 counties, the 

 majority of which produce very small pear crops. 



In Table 38 are shown the results of field examinations made in 28 

 orchards in 1922. These orchards were located in 25 coimties. From 

 the table it appears that 50 per cent of the trees showed infections in- 

 volving 1().9 per cent of the branches on each tree. This is equivalent 

 to 8.5 per cent of all the branches on all the trees, and represents the dam- 

 age done to the trees in a single season of rather mild disease. It is not 

 to be supposed that this injury was uniform on all branches, for injury 

 to branches varies greatly. Such infections, however, usually involve a 

 com]3lete loss of the fruit which would have been produced, and give rise 

 in many cases to cankers in the body of the tree, which may persist from 

 year to year. Such "hold-over" cankers j^rovide an abundance of ma- 

 terial for bringing about new infections the following season. Moreover, 

 the annual enlargement of these cankers usually results in the eventual 

 death of large parts of the tree. 



During the .season of 1923 similar examinations, summarized in 

 Table 39, were made in 10 orchards aggregating 131 acres, and distributed 



• Anderson, H. W. Diseases of nlinols Kiuits. Ml. AKr. Exper. Sta. Clrc. 241 : 71. 

 1S20. 



'PIckell, B. S. Tlic UllKlit of Apples, I'ears and Quinee-s. III. Afir. EJxper, Sta. 

 Circ. 172. 1914. 



