UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



East, especially in the fall or winter, but such an operation is likely to 

 prove of little value in our climate here. Besides, most of those found 

 around the vines were below the reach of any plow. Clean culture in 

 the vineyard will do as much as anything, since ordinarily they feed 

 upon the roots of grasses and other plants at a comparatively short 

 distance from the surface. 



ERINOSE.* 



Erinose is a disease of the vine characterized by swellings on the 

 upper surface of the leaves, and corresponding depressions on the 



lower surface. These swell- 

 ings, when numerous, cause 

 considerable deformation of 

 the leaves, but not the change 

 of color to yellow or brown 

 which is characteristic of 

 most fungous diseases. Even 

 very badly affected leaves 

 retain almost their normal 

 green color on the upper sur- 

 face until late in the season. 

 The depressions on the 

 under side are coated with a 

 thick felt-like covering, 

 which, at first pure white, 

 gradually turns rusty and 

 finally becomes dark brown. 

 Generally, the swellings and 

 corresponding depressions 

 are isolated and few in num- 

 ber on the affected leaves, but in severe cases they are numerous enough 

 to become confluent and the whole lower surface is then completely 

 hidden by the felt-like covering. Occasionally, indeed, the felt-like 

 material extends to the upper surface in narrow strips bordering the 

 veins, and may even be found on the petioles and flower clusters. 



Most of the specimens received at the laboratory are sent under the 

 impression that they are attacked by a fungus, and, in fact, the coating 

 has a strong superficial resemblance to some fungous growths. A micro- 

 scopic examination shows, however, that it consists of a mass of hyper- 

 trophied hairs or abnormal outgrowths of the epidermal cells of the 

 leaf. T.hey are larger, more abundant, and more persistent than the 



* Revised from Bulletin No. 136, by F. T. Bioletti and E. H. Twight. 



FIG. 23. Vine leaf affected with Erinose upper surface. 



