12 APPLE BLOTCH IN SOUTHERN ORCHARDS. 



INFECTION PERIODS. 



The twig cankers in which the apple-blotch fungus passes the win- 

 ter are undoubtedly the chief source of infection. During the warm, 

 moist weather of spring the fungus resumes activity and soon begins 

 to produce spores, which ooze from the pycnidia in enormous quanti- 

 ties. These are readily carried by rain and other agents to the young 

 fruits, twigs, and leaves, producing the first spring outbreak of the 

 disease. According to observations made by the writers in the 

 Ozarks during the past three years, infections begin to take place 

 from four to five weeks after the petals have fallen, and the blotches 

 on the fruit appear about three weeks later. In 1906 the apple 

 petals were off by April 29, and the first spots on the fruit were 

 observed on June 26, two months later, while in 1907 the petals were 

 shed by March 31, a month earlier than the previous year, and the 

 first blotches were seen on May 31. Although the most extensive 

 outbreak occurs at this early period, infections continue to take place 

 throughout the season, } T oung spots being commonly found on the 

 fruit up to picking time. 



As is the case with other fungous diseases, outbreaks of apple 

 blotch are more or less dependent upon weather conditions, although, 

 unlike bitter-rot, it develops in cool as well as in warm weather. 

 Rains or heavy dews are necessary for the germination of the spores 

 and the spread of the fungus from the twigs to the fruit. 



SUSCEPTIBILITY OF VARIETIES. 



There is a great range in the susceptibility of different varieties 

 to apple blotch, some being almost immune, while others under the 

 same conditions become badly affected. Of the commercial varieties 

 grown in the Ozarks, the Ben Davis, Missouri, and Limbertwig are 

 most subject to the disease, the entire crop of these, especially in old 

 unsprayed orchards, often being destroyed. The disease is equally 

 bad on other varieties, such as the Northwestern Greening, Smith, 

 and Maiden Blush. On the other hand, the Winesap, Jonathan, York 

 Imperial, and some others, are almost immune. 



The following is a list of varieties, given in the order of their sus- 

 ceptibility to the attacks of this disease. As this list is based solely 

 upon observations made by the writers during 1906 and 1907, mostly 

 in the Middle West, the arrangement is more or less tentative and will 

 probably have to be changed somewhat when further studies are 

 made : 



Badly affected. — Northwestern Greening, Missouri, Ben Davis, 

 Limbertwig, Red Astrachan, Smith, Maiden Blush, Lawver, Shock- 

 ley, Clayton, Willow, Arkansas Black, and Gano. 



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