404 MANUAL OF FRUIT DISEASES 



attention. Once affected, the plant continues to show signs 

 of yellows annually to some extent. Cases are on record where 

 recurrence of the disease has taken place for nine consecutive 

 years. 



Both healthy and diseased raspberry plants may occur in the 

 same stool. In extended outbreaks all gradations between 

 healthy and affected plants obtain. One of the more striking 

 symptoms of yellows is that the plants are stunted, sickly and 

 bushy in aspect (Fig. 118). In general the condition recalls 

 that of peach-yellows. The fruit-bearing laterals are dwarfed, 

 often being but one-half their normal length. The leaves 

 themselves present an unmistakable characteristic when affected 

 with yellows (Fig. 118). They are abnormally small, and the 

 margins of the upper leaves curl downward (Fig. 118). The 

 tissue between the leaf-veins arches upward, and as a result the 

 veins appear sunken. This uneven growth brings about a 

 curling of the foliage (Fig. 118). In summer, the foliage ac- 

 quires a mottled appearance (Fig. 118) ; at first a light colora- 

 tion prevails, then it gradually changes to a darker green and 

 yellow, and finally is reddish bronze. The colorations accom- 

 panying and symptomatic of yellows vary considerably with 

 the soil and climatic conditions. The disease is more conspic- 

 uous in dry and hot weather. The berries on diseased plants 

 usually become dry before maturity, or they ripen ten to four- 

 teen days early. In case they dry up, the change may be 

 gradual or sudden. If the fruit ripens prematurely, it is bitter, 

 lighter in color, and smaller than normal. Not uncommonly 

 the flowers develop prematurely on the tip of the current year's 

 growth. From all appearances the root-system is normal. 



Cause. 



As yet the causal nature of raspberry-yellows is unknown. 

 Various factors have been assigned in this connection, but 

 always without proof. Among these may be noted fungi, 

 insects, bacteria, poor drainage, lack of soil fertility and other 



