574 SPECIAL PLANT PATHOLOGY 



seems to have spread from the region around Philadelphia as a center 

 has been known about one hundred years. It is a contagious disease of 

 unknown origin. Erwin F. Smith' in 1894 gave the first complete 

 scientific account of yellows founded upon experimental data. He 

 describes the symptoms as follows: "Prematurely ripe, red-spotted 

 fruits, and premature unfolding of the leaf buds into slender, pale 

 shoots, or into branched, broom-hke growths. The time of ripen- 

 ing of premature fruit varies within wide limits; sometimes it pre- 

 cedes the normal ripening by only a few days, and at other times by 

 several weeks. The red spots occur in the flesh as well as on the skin, 

 making the peach more highly colored than is natural. The taste of 

 of the fruit is generally inferior and often insipid, mawkish, or bitter. 

 Often this prematiu-e ripening is the first symptom of yellows. Often 

 during the first year of the disease this kind of fruit is restricted to cer- 

 tain Umbs, or even to single twigs, which, however, do not differ in 

 appearance from other hmbs of the tree. The following year, a larger 

 part of the tree becomes affected and finally the whole of it, the parts 

 first attacked now showing additional symptoms, if they have not 

 already done so. These symptoms are the development of the winter 

 buds out of their proper season. The buds may rush into shoots only 

 a few days in advance of the proper time in the spring, or may begin to 

 grow in early summer, soon after they are formed, and while the leaves 

 on the parent stem are still bright green. This is a very common and 

 characteristic symptom, and is especially noticeable in autumn when the 

 normal fohage has fallen. Usually under the influence of this disease 

 feeble shoots also appear in considerable numbers on the trunk and main 

 limbs. These arise from old resting buds, which are buried deep in the 

 bark and wood and remain dormant in healthy trees. Such shoots are 

 sometimes unbranched, and nearly colorless, but the majority are green 

 and repeatedly branched, making a sort of broomlike, erect, pale green, 

 slender growth, filling the interior of the tree." 



Yellows can be well controlled by destroying the diseased trees as 

 soon as they show premature fruit, or shoots with the narrow yellow 

 leaves. The best treatment is to pull out or grub out and burn the dis- 

 eased trees, and remove the stumps at a more convenient time. This, 

 however, does not remove all source of infection as the disease may pos- 

 sibly spread from the stumps or yellowed shoots arising from them. 



» Smith, E. F.: U. S. Farmers' Bulletin No. 17, 1894. 



