•252 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



These epochs have been fixed accordhig to the periodical develop- 

 ment of black rot. Prunet, who examined black rot very closely, 

 points out the parallelism between the evolution of the j^arasite and 

 that of the vine, and has based on this fact a rational course of treat- 

 ment, here given in full. The first invasion especially attacks the 

 leaves, which on the vine branches, the first shot forth, are included 

 between the third and the eighth ; the second attacks chiefly those in- 

 cluded between the tenth and the eighteenth, and in addition the 

 pedicles of the flower and grape stalks ; the third attacks the fruit 

 when they are the size of a big pea, and also the leaves above the 

 eighteenth ; finally, the last attacks the fruit when of almost normal 

 size. With such data, we ought to operate according to the intensity 

 of the disease. 



I. In the most intense hotbeds of disease. 



second 



Where vineyards have been treated as soon as the disease appears 

 success is complete and the disease easily overcome. However, if the 

 formidable fungus has been allowed to develop without any obstacle 

 before treatment, the perithecae which spread the disease are so 

 numerous that very often ten treatments do not give a complete result. 

 This is especially the case when by negligence the black-rotted grapes 

 have been left on the stock. It is thus advisable to support the spring 

 and summer treatments by energetic winter treatments and by pre- 

 cautions which complete these treatments. In spring and in summer 

 the spotted leaves must be removed ; if one is surprised by the disease 

 remove the buds and young branches from the stock so that the stem 

 may be better aerated, and that the axillary sprouts do not form a 

 dangerous neighboiu^hood for the grapes. In winter the leaves and 

 attacked grapes left on the stock must be burned, then the stocks must 

 be treated as for anthracnose by concentrated and acidulated solutions 

 of green vitriol, so as to destroy, if possible, all the perithecae which 

 the following year transmit the disease to the vine. The strong doses 

 of blue vitriol which enter into the composition of the bouillie used to 

 combat black rot render the struggle against this disease very onerous, 

 and almost impossible in districts where low quality wine is produced 

 at a low price. Numerous trials have, therefore, been made with 

 weak bouillie. In America especially it has been tried to overcome 



