DRUPACEOUS FRUITS 129 



Die back {Valsa leucostoma (Pers.) Fr.). — This disease 

 of limbs, trunk, and twigs is serious in Europe and Australia. 

 It was first described in the United States by Rolfs of 

 Missouri in 1907,' who noted it upon peach and Japanese 

 plum. 



Infection occurs upon buds or wounds during the growing 

 season, and in early winter and spring the tips of young 

 branches, especially water sprouts, are killed back from 2.5 

 to 46 cm. As many as 300 such dead twigs have been 

 noted on a single tree. It develops most rapidly in a 

 warm spell following freezing weather in the spring, and is 

 more serious upon trees which have been weakened by 

 any cause. 



Twigs killed during the winter show at first a dark, pur- 

 plish skin, changing later to leathery, scarlet, or purple, 

 finally drab. Then the skin loosens and wrinkles. At this 

 time black pycnidia appear under the skin. These soon 

 push out a white cap through a transverse slit in the skin, 

 and in wet weather exude very fine red threads of spores. 

 Gum flow usually accompanies the constriction, mafking 

 the juncture of dead and healthy wood. During summer, 

 leaves on infected twigs frequently wilt, owing to the gir- 

 dling of the stem. Upon the trunks large wounds, often 

 regarded as sun scalds, are produced, while upon j'oung 

 limbs the wounds appear as enlargements or " knots." 

 Large limbs or even whole trees succumb. 



Excision should be practiced. 



Blight, shot hole (Coryneum Beyerinkii Oud.). — This 

 disease, which has been troublesome in California for 

 years, often destroying the crop and weakening the trees, 



1 Rolfs, F. M., Sci. n. s. 26, 87. 



