182 MANUAL OF FRUIT DISEASES 



susceptible. Sour cherries are slightly or not at all attacked. 

 Sweet cherries, on the other hand, are very susceptible to bac- 

 terial gummosis. The Bing and Napoleon (Royal Ann, Ox 

 Heart), two very desirable cherries in the Northwest, suffer 

 considerably from bacterial-gummosis. Certain sweet varieties, 

 however, like the Lambert and May Duke, are comparatively 

 resistant. 



Symptoms. 



This disease is most serious on trees which have been set for 

 three or four years. In many cases they may be killed. On 

 trees more than ten or twelve years old the damage is largely 

 a blighting of the smaller branches, spurs and buds, and it is 

 usually not serious. 



Often there is little indication of the disease until whole 

 trees or branches fail to leaf in the spring, or until there is a 

 sudden wilting in the growing-season. Careful examination of 

 cherry trees showing such symptoms will usually reveal a 

 girdling of a limb or trunk. Sometimes there is no gumming, 

 but ordinarily a more or less copious flow of gum accompanies 

 such a condition (Fig. 50). The amount of gum exuded from 

 lesions is no indication of the amount or severity of the disease. 

 On cutting into the bark at affected points the inner tissues 

 will be found to be brownish and the appearance will indicate 

 approaching death. A sour odor may accompany this condi- 

 tion. The lesion produced on the woody parts is a canker. At 

 first the bark is discolored. The discolored area enlarges and 

 the surface of the bark becomes depressed. Then gum exudes 

 from the margin of the canker. Subsequently the extension 

 of the canker ceases and a callus develops about its margin. 

 Enlargement of the cankered area takes place in the winter and 

 early spring, but ceases by the last of March. The callus is 

 formed in the spring and summer. The next winter the callus 

 may be attacked and the lesion extended. In the spring a 

 second callus is formed. This process may be repeated annually 



