DISEASES 



211 



Countless numbers of bacilli are contained in the beads of the 

 gelatinous substance, and are readily spread to the blossoms and 

 branches by bees and other insects. They multiply rapidly in the 

 nectar of flowers, from which they spread into the softer tissues of 

 the young twigs. Injuries to the young growth and biting insects 

 may assist the organism in gaining entrance to the growing tissue. 



Brief exposure to direct 

 sunlight or a period of dry 

 weather often results in de- 

 stroying the bacillus. 



Where conditions are favor- 

 able the disease may winter 

 over ; but since considerable 

 moisture and protection from 

 drying out are necessary for 

 successful wintering, and since 

 relatively few twigs offer these 

 winter conditions, it is evident 

 that the disease does not ex- 

 tensively winter over. 



The control methods con- 

 sist in thoroughly pruning all 

 diseased tissue and cutting 

 each twig an inch or more be- 

 low the visibly affected part. 

 It is possible practically to 

 control this disease if the 

 pruning is carried on with 

 great care and thoroughness. 



Bitter rot (Glomorella rufomaculans). This disease appears as 

 cankers or sunken areas on the bark and may be found on the 

 limbs of the trees, where it generally passes the winter. Beneath 

 the bark the wood growth dies and cracks open. It seems highly 

 probable that there is a relation between the canker on the limbs 

 and the summer form of the disease on the fruit. Duggar 1 likens 

 the relation to a pyramidal area at the apex of which is found 

 the cankered limb and below it the ever-increasing area of the 



1 B. M. Duggar, Professor of Plant Physiology in Cornell University. 



Fig. 92. Bitter rot 



Stem of young tree one month after inoculat- 

 ing with fungus. (University of Maine) 



