20? 



of the trees infected and 9.4 per cent of the fruit noticeably marred by 

 scab infection. Were it possible to include the much more severe in- 

 fections commonly encountered in smaller orchards, these figures would 

 be greatly increased. 



Control of scab consists in the timely and thorough application of 

 effective sprays. Infection takes place in spring from the overwintering 

 spores, which are usually ready to begin their work between May 10 and 

 May 20 in Illinois, when they take advantage of any moist period to 

 produce infection. Application of sprays jitst previous to predicted 

 rains during the middle fortnight of May should succeed in keeping the 

 disease under control. 



Blotch 



Caused by Phyllosticia solitaria E. & E. 



Blotch, next to scab the most serious apple disease found in Illinois, 

 attacks twigs, stems, fruiting spurs, leaves, and fruit. Its chief damage, 

 however, consists in the injury done to the fruit. On susceptible varie- 

 ties it may kill fruit spurs and thus considerably reduce the yield. 



The early history of blotch in Illinois is unknown. The disease first 

 appeared in the United States about 1895, and its spread has been very 

 rapid. Burrill reported blotch as occurring in 8 counties in 1911 and 

 again in 5 counties in 1913. Its present distribution is shown on ]\[ap 

 42, which illustrates the southern distribution of the disease and its ex- 

 tension westward and northward with commercial apple-growing. It 

 is known to occur in 63 of the 102 counties of the state. 



The crop reductions from blotch attack have been estimated, as 

 shown in Table 31, to have increased from 3 per cent in 1918 to 5.5 

 l)er cent in 1923. 



The severity of this disease, when sprajs are not a[jplied. is illus- 

 trated in Table 32, which summarizes observations made during 1923 

 in ]() orchards distributed among 14 counties and including 131 acres. 

 Practically 100 per cent of the trees were infected, and 90.4 per cent 

 of the fruit was diseased. The effect of a thorough application of sprays 

 is shown, on the other hand, by an examination made in the same year 

 in 7 commercial orchards distributed among 5 representative counties. 

 These orchards included 20.") acres and showed only 25.2 (ler cent of 

 the trees infected, with 2.5 per cent of the fruit diseased. 



Fire-blight 

 Caused by Bacillus amylovorus (Burr.) Trev. 



This disease, the oldest and best known of apple diseases in Illi- 

 nois, attacks every above-ground part of the tree. Blossoms and leaves, 

 when diseased, look as if scorched by fire and burned black. On branches 

 ancl trunks cankers are formed, from which an exudate is given off. 



