BULLETIN 192. INSECTS INJURIOUS TO THE VINE. 135 



normal leaf-hairs of the leaf, and differ also in being often branched 

 and usually unicellular. This abnormal growth, in common with 

 similar growths found on other pl'ants, is called an erineum, from a 

 Greek word meaning woolly. This is the derivation of the word erinose, 

 which means woolly disease a very appropriate name. The erinea of 

 leaves were formerly supposed to be of fungous origin, but are now 

 known to be due to the attacks of minute mites. The feeding of these 

 mites exert a stimulating effect upon the epidermal cells of the leaf, 

 which causes them to grow out into the abnormal hair-like processes 

 already described. The mite causing erinose of the vine is known as 

 Eriophyes vitis, and is related to the mites causing a similar disease of 

 the walnut and the leaf blister of the pear, both of which are very 

 common in California. 



The Eriophyes vitis is not a true insect, but a mite or acarid belong- 

 ing to the class of Arachnida to which belong also spiders, scorpions, 

 ticks, and our common red spider so destructive to fruit trees. These 

 mites are extremely minute, and only a practiced eye can perceive them 

 among the tangled mass of erineum on the leaf, by the aid of an ordinary 

 hand magnifier, and then only with great difficulty. 



Amount of Injury. Erinose was formerly considered to be a very 

 serious disease of the vine, owing to the fact that its effects were con- 

 fused with those of the powdery mildew. It is only in very exceptional 

 cases that it is, alone, capable of doing serious injury to the vine or its 

 crop. When accompanying oidium or drought it may, however, per- 

 ceptibly increase the damage due to these causes. When very abundant 

 it may seriously interfere with the growth of young vines, but accord- 

 ing to Mayet, never damages old vines, except by interfering slightly 

 with the ripening of the canes, or at most causing an almost impercep- 

 tible diminution of crop. All varieties of vines are not equally attacked. 

 According to Ravaz, certain American species such as Berlandieri, 

 Mustang, Cinerea, Cordifolia, and Scuppernong are immune. All vari- 

 eties of Vinifera are susceptible, but not equally. Of varieties culti- 

 vated in California, Sauvignon, Sirah, Marsanne, and Gamay Teinturier 

 are said by Ravaz to be little subject to attack; while Aramon, Cinsaut, 

 and Frontignan (Small Muscatel) are very susceptible. The worst 

 cases so far observed in California have been on Flame Tokay and 

 Mission, but it has been found also on other varieties, among them 

 Zinfandel and Muscat. 



Distribution in California. The first specimens of erinose received 

 by the Experiment Station we-re sent from Windsor, Sonoma County, 

 in 1896. The next year affected leaves were received from Healdsburg 

 and Dry Creek, in the same county. All these cases were upon Mission 

 vines. Since then specimens of the disease have been received from 

 nearly every grape-growing county of the State. 



