208 



Spread of the disease is accomplished by insects and to some extent by 

 the wind. 



The history of this disease in IlHnois, as indicated by discussions in 

 the Transactions of the Illinois Horticultural Society, is practically co- 

 extensive with apple-growing ; and while the injury to apples is not so 

 great as to pears and quinces, the loss to the state is larger because of 

 the greater importance of the apple crop. 



Damage done by this disease is often very severe. In 191i' it was 

 placed at $500,000 for one county and at $1.-500,000 for the state as a 

 whole. For the period 1918-1923, inclusive, the crop reduction has 

 varied, as shown in Table 33, from a trace in two seasons to 1.5 per 

 cent in two other seasons. The equivalent reduction in bushels has 

 ranged from 3,000 to 112,000 bushels and the valuation from $7,500 to 

 $128,000. 



The known distribution of fire-blight is shown on ]\Iap 43. There 

 are only 13 counties in the state in which this disease is not known to 

 occur. 



There is no satisfactory means of control. Cutting out diseased 

 parts with tools sterilized in a 1-10(10 mercuric chloride solution is help- 

 ful in a new orchard, but in old orchards the only effective measure is 

 the prompt eradication of blight cankers. 



Rust 

 Caused by Gyinnosporangiitm juniperi-virginianac Schw. 



Rust is one of the very common apple diseases found in the state. 

 Leaves and fruit are especially susceptible to attack. Leaf injury and 

 defoliation, if severe over several seasons, markedly stunts the growth 

 of trees. On the fruit, rust spots cause malformation or disfiguration, 

 which prevents the fruit from being marketed as first-class produce. 



According to Burrill,'- rust has been present on apples in Illinois 

 since 1881 or 1882. The earliest actual collection was made by a Mr. 

 Snow in Perry county in 189G. G. P. Clinton made two collections in 

 1898, one in Washington county and one in Marion, and a further col- 

 lection was made in Richland county in 1899 by a Mr. Woodworth. 



In 1911 Burrill found the disease in 5 widely separated counties and 

 in 1913 in 2 counties additional. The known distribution of a]iplc rust 

 at the ])resent time is shown on Ma|) J4. 



The damage resulting from the attack of this disease is estimated 

 by Anderson^ to be over $25,0(iO annually. Estimates of crop reduc- 

 tions made for the years 1919-1923, inclusive, and reproduced in Table 

 34, range from a trace to 1.5 jicr cent, annually amounting to between 



' rickett. B. S. The blieht of npples. pears ami quimes. HI. Art. EXper. Sta. 

 Circ. 172. 1014. 



-Tarasitic funei of Illinois. Rul. Ul. State Lab. Nat. Hist. 2: 240. 188.i. 



■' Disea.sis of Illinois Fiuits. 111. Aki-. Exper. Sta. Ciri-. 241 : 37. 1920. 



