206 



Diseases of Fruits 

 Apple 



Among the fruits grown commercially in Illinois the apple is by far 

 the most important. While production varies greatly from year to year, 

 the value of the state's crop always runs into large figures. Since 1916 

 the lowest yield has been 2,381.000 bushels and the highest 9,720.000. 

 The lowest valuation has been $.5,575,000 and the highest $10,206,000. 

 The commercial crop is much less than this, ranging since 1920 from 

 397,000 to 1,620,000 bushels, and from $2,977,000 to $6,845,000 in valua- 

 tion. 



The relative importance of apple-production in Illinois by counties 

 for 1919 ^ is indicated on Map 40. from which it may be seen that the 

 chief apple-producing section of the state lies southwest of a line drawn 

 from the northern boundary of Hancock county to the northern, boundary 

 of Clark county. North of this line production is mostly incidental and 

 comes chiefly from small farm orchards maintained for the convenience 

 of the owners, only the surplus reaching the markets. 



Scab 

 Caused by Venturia inaeqiialis (Cke.) ^^'int. 



Scab is probably the most common apple disease occurring in Illi- 

 nois. It has been known in the state at least since 1863, in which year 

 it is mentioned in the Transactions of the Illinois Horticultural Society 

 as occurring in Ogle county. During subsequent years its occurrence 

 is noted in these Transactions in Carroll, Ogle, Bureau. Tazewell. Cham- 

 paign, Adams, Pike, Cumberland, Madison, Marion, Jetferson, Rich- 

 land, Union, and Johnson counties. 



The distribution of scab in the state is shown on ^lap 41. In 10 

 counties only, of the 102 of the state, has its presence not been demon- 

 strated, and even in these counties it is probably present. 



This disease attacks the leaves, the flowering parts, and the fruit, 

 and results in a reduction in the quantity of fruit set, in leaf injury and 

 early defoliation, and in fruit-spotting. It also increases the number of 

 windfalls. Crop reduction occasioned by this injury is great and has 

 been estimated for a 5-year period ending with 1923. as recorded in 

 Table 29, to have ranged from 3.5 per cent in 1923 to 12 per cent in 

 1921. In crop reductions these percentages are equivalent to 277.000 

 bushels valued at $318,000 in 1923. and to 387,000 bushels valued at 

 $967,500 in 1921. 



The seriousness of scab is illustrated in Table 30, which shows that 

 in 18 counties in central and southern Illinois 23 representative orchards 

 examined in 1923, including 1728 acres, had an average of 12.7 per -cent 



" U. S. Census BuUetin for 1920. AKricuUuro: lUinois. Statistics for the state 

 and its counties. 



