8 BULLETIN" 534, U. S. DEPARTMENT OF AGRICULTURE. 



the first sprajdng for the prevention of blotch infections should be 

 well under way when three weeks have elapsed after petal fall. This 

 is particularly true during a season of belated blooming due to cold 

 or otherwise unseasonable weather, as the period of growth and ma- 

 turity of the fungus and its spores does not seem to be influenced so 

 much by such conditions as does the blooming period of the host. 



As determined by artificial inoculations, Phyllosticta solitaria grows 

 very slowly and is not perceptible on the fruit until three to six 

 weeks after infection has taken place. Ordinarily the blotched areas 

 are not large enough to appear conspicuous before the early part of 

 July. 



* CULTURAL RELATIONS. 



Phyllosticta solitaria will grow on a wide range of culture media. 

 It will also produce pycnidia on all of the ordinary solid culture 

 media. These pycnidia, however, do not produce spores. The only 

 medium on which the writer has been able to grow the fungus with 

 the formation of both pycnidia and spores is sterile apple wood, 

 which was the medium used by Scott and Rorer. Even on this me- 

 dium two to three months elapsed in the case of all the strains used 

 by the writer before mature spores were produced. 



WEATHER CONDITIONS. 



In orchards in which twig cankers are abundant, dry weather does 

 not appear to reduce greatly the number of infections, because prac- 

 tically every apple is affected anyway; but in the average blotch- 

 infected orchard of the Ozark section the reduction is very notice- 

 able. In 1914 the absence of rain during the latter half of May and 

 during the first three weeks of June greatly reduced the number of 

 infections. In Arkansas the period of heaviest infection did not 

 occur until about July 1. In Kansas, where blotch is a particularly 

 serious disease, it was found, as Lewis had noted previously in dry 

 seasons, that the disease was not greatly hindered by the dry weather. 

 The sources of infection, that is, twig cankers, are much more abun- 

 dant in Kansas than in Arkansas, and even if a large proportion of 

 the expelled spores failed to germinate there would still be enough 

 to infect the fruit heavily. Undoubtedly, as in the case of most 

 fungous diseases, moist weather is particularly favorable for the oc- 

 currence of the maximum number of blotch infections. 



The writer has never been able to note any relation between the 

 amount of infection and the temperature extremes during May and 

 June. Neither extreme appears to be particularly favorable or par- 

 ticularly unfavorable. 



