OBSERVATIONS ON SOME VINE DISEASES IN SONOMA COUNTY. 



When the berries become affected just previous to maturity, or after 

 maturity has begun, they ripen imperfectly and, as a rule, are never 

 worth picking. The clusters of diseased grapes are generally allowed 

 to remain on the vine, and, after defoliation, they may be observed 

 hanging from the canes. 



Effect of the Disease on the Shoots. The shoots are not affected directly 

 by the Red-leaf disease. The symptoms they show are a consequence, 

 so to speak, of the intensity of the malady on the leaves. When the 

 shoots are partially defoliated (counting from the apex), their growth 

 is only checked for a while. When the defoliation is more severe, the 

 apex curls somewhat, discolors and dies. Death, however, is not con- 

 fined to the apex, but proceeds for a greater or less distance down the 

 shoots, the discoloration progressing, as it were, by stages. The shoots 

 shrink and gradually turn brown. The shrinkage of the tissues is most 

 noticeable near the nodes, and, except in more lignified parts of the 

 shoots, always precedes the discoloration. The discoloration of the 

 shoots is somewhat irregular, and more rapid in the parts exposed to 

 the sun. When defoliation is complete, the shoots sometimes die from 

 apex to base. When they are not defoliated, their lignification does 

 not seem to be materially interfered with, though it is often irregular. 

 One may even find, in rare cases, green immature spots or stripes in 

 the midst of lignified tissue, but even such an irregularity as this does 

 not persist. The immature spots mature in time. 



The Relationships of the Red-leaf Disease. The Red-leaf disease 

 appears more or less closely related to the Folletage, the Rougeot, and 

 the California Vine disease. It resembles the Folletage by the sporadic 

 suddenness with which it sometimes appears; the Rougeot, in its not 

 being immediately fatal, and possibly also in some of its foliar colora- 

 tions; and the California (Anaheim) vine disease in the striping of the 

 leaves. 



The cause of the Folletage and of the Rougeot has been thought to be 

 due to the rupture of equilibrium between transpiration and absorption, 

 but that of the California vine disease has not been determined. In 

 the case of the Red-leaf disease, the evidence gathered in a single season 

 seems to point to a physical rather than to a parasitic cause. 



Resemblance between the Red-leaf Disease and the Folletage. The 

 Folletage affects the vines in midsummer. "One* sometimes observes, 

 especially in July and August, vines in excellent health dying suddenly 

 in a vineyard. The leaves wilt, fade, and dry; the shoots and even the 

 arms succumb. The vines may die in a few minutes. * * * It is 

 only isolated vines (they may sometimes be numerous) which are 

 affected by this disease; * * * a whole vineyard is never affected. 

 Entire shoots, or even whole arms, may be destroyed on a diseased vine 



*P. Viala: " Les Maladies de la Yigne," page 471. 



