PEACH DISEASES 301 



an enlargement at the point of injury. Evidences of the 

 disease are noticeable in late winter or early spring months. 

 Affected twigs are at first purplish, but later scarlet, and leathery. 

 Still later the bark becomes drab-colored, loose and wrinkled. 

 Finally black pustules of the pathogene appear under the bark 

 in these grayish areas. These fruiting bodies break through 

 the bark and become covered with a silvery-white coat, thus 

 dotting the whole diseased portion in a characteristic manner. 

 This condition is often spoken of as silver-twig. Twigs and 

 water sprouts are killed back in mid-winter or later. This 

 killing occurs repeatedly until finally the affected tree is given 

 a ragged appearance. During the growing season an affected 

 limb or twig may be girdled, in consequence of which the foliage 

 assumes a yellowish aspect, then suddenly wilts and dies. 



Cause. 



While the causal factor is designated as the fungus Valsa 

 leucostoma var. cincta, the general opinion prevails that other 

 factors such as frost, unfavorable soil, lack of cultivation and 

 other neglect play an important role in the production of the 

 die-back disease. Indeed, some prominent authorities hold 

 that the prime cause is the action of low temperatures. The 

 fungus may in any case be regarded as an exciting cause 

 at least, and in its absence the other above-named factors 

 would doubtless exhibit less influence in bringing about the 

 trouble. The pathogene characteristically attacks trees in 

 a weakened cbndition, like those injured by frost and fire. 

 And this is a real source of danger, inasmuch as such trees 

 when taken at this disadvantage suffer injury far in excess of 

 that induced by frost alone. Furthermore the semi-parasitic 

 nature of the fungus allows it to live indefinitely about the 

 orchard on dead limbs, ready to attack any trees that are in 

 poor condition. A warm spell in the spring followed by a 

 freeze renders the tissue of the peach-limbs favorable to the 

 growth of the fungus. 



