578 TEXTBOOK OF BOTANY 



1881 of an important fungicide known as Bordeaux mixture. A disease 

 caused by the root louse ( Phylloxera ) had become a serious menace to 

 the vineyards of France, and in order to combat this disease the French 

 imported some American grapes which are immune to the root louse. 

 The American stock, however, was infected with the downy mildew 

 fungus which then spread all over Europe. Apparently at least one 

 vineyard-keeper customarily sprinkled a copper sulfate-lime mixture on 

 the vines along the highways to discourage theft of the grapes. The 

 French pathologist, Millardet, observed that where such a mixture was 

 sprinkled on the vines, the ravages of mildew were reduced. He began 

 experiments which led to the general use of Bordeaux mixture as a 

 spray for the successful control of this and other diseases. 



The fungus attacks all green parts of the grape plant and appears as 

 whitish patches of mildew. The fungous hyphae enter the plant largely 

 through the stomates. The presence of the mycelium within the plant 

 may result in loss of leaves, dwarfing of young twigs, and destruction of 

 fruit. Since the fungus winters over as spores in fallen leaves, the disease 

 may be combated by getting rid of the leaves (sanitation), and by 

 spraying the plants with Bordeaux mixture before the young hyphae 

 from the spores invade the young leaves and flowers. 



The powdery mildews. The powdery mildews occur everywhere in 

 temperate and tropical regions and on a large variety of hosts. These 

 fungi are visible on the surface of the affected plant, and sometimes the 

 parasitized tissues of the host become malfoiTned. They are either 

 whitish to grayish, powdery or mealy depending upon whether the 

 visible stiTicture is the mycelium, the summer spores, or the blackish 

 fruiting bodies. The powdery mildews are always superficial parasites 

 and in this way differ sharply from the downy mildews considered 

 above. The methods recommended for the control of powdery mildews 

 include removing the infected parts, or using an appropriate spray 

 or a sulfur dust. 



Brown rot of stone fruits. This disease is important in the United 

 States and Europe because it destroys the fruit of such orchard crops as 

 peaches, plums, cherries, and apricots (Fig 261). Among the pome 

 fruits the apple may also be affected. The disease is usually recognized 

 by the rotting of fruits, blasting of flowers, and the killing of young 

 stems. A brown spot appears on the fruit and may enlarge until the 

 whole fruit is decayed. In later stages the fruit dries and shrivels to a 



