DISEASES OF PEARS 1049 



This cracking is commonly associated with the presence of the 

 disease on the Flemish Beauty. On the twigs, the disease appears 

 as blisters, which later break open, giving the twig a rough scabby 

 appearance. 



The disease is caused by the fungus Venturia pyrina, which 

 produces its summer spores in abundance in the scab spots. These 

 spores are commonly disseminated by wind, and during cool moist 

 weather will germinate and infect the tender leaves, fruit, or twigs. 

 Such infections result in new spots that in turn produce more 

 spores. 



While it is known that the fungus may pass the winter in lesions 

 on infected twigs where summer spores are produced the follow- 

 ing spring, it has been shown that it also passes the winter in the 

 fallen leaves that were scabby when alive. On these leaves mi- 

 nute fruit bodies are produced from which during April or May 

 sexual spores are discharged, and these caught by air currents 

 are carried to the opening buds. Early infection takes place from 

 these during favorable weather. 



Methods of Control 



The disease on pears may be more difficult to control than apple 

 scab because the fungus is able to pass the winter in infected 

 twigs. However, thorough applications of either bordeaux mix- 

 ture, 4-4-50, or lime-sulphur solution, 1-50, made at the proper 

 time will give good results, especially if made year after year. 

 Foliage injury has sometimes resulted from an application of lime- 

 sulphur so that bordeaux mixture may be preferable. The first 

 application should be made when the petals show pink but before 

 the blossoms open; the second, soon after petals fall; and a 

 third, about two weeks later. As in the case of apple scab, other 

 applications may be necessary if wet weather prevails. 



LEAF SPOT 



In the United States leaf spots occur commonly wherever pears 

 are grown, in both nursery and orchard. While Kieffer and a few 

 others show resistance, most varieties are susceptible in varying 

 degrees. The disease occurs only on the leaves, but the tree may 

 be reduced in vigor from an early defoliation brought about by an 



