HACKBERRY DISEASES 175 



The first indication of the diseased condition can be detected 

 by examining the buds in the winter. Diseased buds are 

 found on wood one year or more old. They are larger in diame- 

 ter than healthy buds of the same length, grayish in color and 

 more open and hairy. When closely examined, it is seen that 

 the scales and inner bud-parts are distorted and enlarged, 

 causing the scales to stand open, exposing the inner parts. 

 Inside of the scales small mites are found. The mycelium of 

 the mildew fungus covers the outsides of the scales and the 

 small black fruiting-bodies of the mildew may be found within 

 the bud on the inner scales and young leaves. The buds of 

 the diseased laterals are more numerous than is normal and they 

 are usually all diseased. Many diseased buds are formed at 

 the bases of these laterals from which develop a new knot 

 with stubby dwarfed branches. The mycelium of the powdery 

 mildew fungus covers the buds and twigs early in the spring 

 and even at times is found on the under sides of the leaves of 

 diseased branches. This causes a whitish powdery appear- 

 ance of these parts. 



Ca^lse. 



Two causal agents are always associated with the diseased 

 buds which develop the knots and broom-like growths. One 

 is a gall-mite, a species of Phytoptus, and the other a powdery 

 mildew fungus, Sphcerotheca phytoptophila. It has never 

 been definitely determined which of these two agents is the 

 more responsible in producing the abnormal growths. The 

 gall-mites are known to cause galls and warts of leaves and 

 twigs and in some instances other powdery mildews have been 

 found growing on the diseased areas produced by these insects. 

 Since, however, the mildew fungus is found growing over and 

 within the diseased buds and the fruiting-bodies are already 

 fully formed within the unopened buds, it seems reasonable to 

 believe that the fungus is present from the very initiation of 



