692 Journal of Agriculture . Victoria. [10 Nov., 1917. 



bunches are thus attacked before or shortly after blossom, they are said 

 to suffer from gi-ey rot. If infested when half their full size, the berries 

 first become soft, and later dry out. This form of the disease is knowu 

 as brown or soft rot. 



How Damage is Done. 



Mildew may destroy the crop in three different ways. If it 

 appears early, just before, during, or just after blossoming, it may 

 invade the young bunches, causing them to dry and fall off. This form, 

 which is termed grey rot, has been known to destroy the entire ci-op in a 

 couple of days in certain moist districts of France. Brown rot, when 

 the berries are rather more than half their full size, is also responsible 

 for much loss. Once the berries commence to change colour, the fungus 

 is no longer able to penetrate the tissues; the fruit is safe from infec- 

 tion. 



The most usual way in which injury is caused, however, is by 

 bringing about a premature fall of leaves ; badly infested leaves drop 

 off, often at the junction with the stalk, which is left adhering to the 

 canes. Vines thus stripped of their leaves cannot ripen their fruit 

 properly. Grapes borne by vines affected with Mildew yield but little 

 juice, and the wine made from them is of very poor quality — 'Only fit 

 for distillation. The must is rich in nitrogenous substances and unsuit- 

 able for the healthy growth of yeast. Not only is the current season's 

 crop injured, but that of the following season is seriously compromised, 

 since the premature stripping of the leaves prevents the accumulation 

 of reserve substances in the vine, so that the following season few 

 bunches are formed. The damage is similar to that caused when the 

 foliage of the vineyard is fed off by stock too soon after vintage. 



Life History. 



Space will not here permit of more than a brief outline. The 

 botanical name of the fungus is now Plasmopara viticola. Formerly it 

 was known as PerO'nospora viticola. It is closely related to Irish Blight 

 of the potato. Like most fungi which prey upon the vine and fruit 

 trees, but in striking contrast to that of Oidium, the mycelium* grows 

 in the interior of tlae host plant. It is only the fructifications bearing 

 the summer spores which are outside. This internal nature of the 

 mycelium is of vital importance in connexion with treatment, which 

 cannot possibly be curative, as sulphuring is in ease of Oidium. f The 

 mycelium develops in the inside of the tissues, which are disorganized 

 and broken down under its influence, thus causing the '' oil spots " 

 already described. After a time, but only if weather conditions are 

 sufficiently moist, the fungus sends out, through the stomata or breath- 

 ing pores on the under side of the leaf, strands bearing oonidia or 

 summer spores. These conidiophores, as they are called, somewhat 

 resemble a bunch of grapes, the conidia being the berries (see Fig. I.). 

 It is thousands of these, massed closely together, which constitute the 

 white down characteristic of the fungus. 



* Mycelium, according to de Bary, is the vegetati'\'i- portion of thallus of fungi, composed of one or 

 more "hypllae." It is the growing (and feeding) portion of the fungus as distinguished from the spore- 

 bearing or reproductive part. In edible, cultivated mushrooms it is popularly known a8 spawn. 



t In the case of Oidium the mycelium is on the outride of the tissues ; it is only the suckers sent out 

 from it which penetrate the o\it«r skin of the vine to absorb nmirishment. 



