PEAR GROWING IN CALIFORNIA. 



367 



PEAR SCAB. 



Next to pear blight scab is the most serious disease of pears. Unlike 

 the blight, which affects the tree itself, scab attacks the fruit and 

 foliage. Despite spraying methods, which are satisfactory in the con- 

 trol of this disease it annually causes a heavy loss of pears because of 

 inattention to spraying or because of faulty methods or failure to make 

 applications at the right time. 



Pear scab is due to a fungus called 

 Venturia pyrina. Its occurrence is 

 common throughout the pear-growing 

 districts of the state, but more or less 

 seasonal. For example, in 1915 there 

 was practically none of the disease in 

 the pear-growing districts of the Sac- 

 ramento Valley. Spraying could not 

 account entirely for the almost total 

 absence, as there was little or no scab 

 in orchards not sprayed. In 1916 just 

 the reverse was the case and except in 

 orchards where the spraying was done 

 just right and at just the proper time, 

 there was so much infection that a large 

 percentage of the pears were not fit to 

 pack and were utilized by the canneries 

 with considerable wastage. Again, in 

 1917 the scab was not at all bad in the 

 Sacramento Valley and wherever the 

 least effort was made to control it little 

 difficulty was experienced with its 

 attack. Weather conditions are no 

 doubt responsible for the prevalence of 

 the disease during certain seasons. As 

 humidity, and heat generally, favor the 

 development of any fungous trouble we 

 would expect such conditions in the 

 early spring, as the buds are unfolding 

 to favor the development of this fun- 

 gus. 



The presence of the disease in an orchard is recognized by sooty- 

 like blotches on the underside of the leaves and bluish, more or less 

 circular roughened patches on the surface of the pears. As the fungus 

 dies and becomes inactive these patches change to brown, roughened, 

 scabby areas which check the growth of the fruit at places of attack, 

 thus causing distortion and abnormally-shaped pears as the one 

 shown in Fig. 161. The injury to the fruit is local, affecting princi- 

 pally the surface, and causing slight discoloration and noticeable 

 hardening underneath the skin. But for the distortion scabby pears 

 would not be nearly so objectionable. 



FIG. 160. Pear leaf showing 

 infection with scab fungus, Ven- 

 turia pyrina. 



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