Chapter 11. 
DISEASES OF LEAVES AND SHOOTS (contd.). 
Black-Leg or Wilt Disease of Asters. Tomato-leaf rust or 
mould Leaf-blotch of Cucumber. Mildews of Roses, Goose- 
berries, etc. 
The Black-Leg or wilt disease of asters is extremely 
prevalent wherever asters are grown. It is caused by a 
species of Phytophthora, which differs in several respects 
from Phytophthora infestans, the cause of the Late-Blight 
disease of potatoes. The disease may manifest itself at 
any stage in the life of the aster, but the initial attack is 
always upon the seedlings. In severe cases the seedlings 
collapse, as in the “Damping-off” disease caused by 
Pythium, but more frequently they harbour the fungus 
without showing any outward sign of disease at this stage. 
Such seedlings may wilt and collapse when transplanted, 
but many succeed in surviving even to the flowering stage 
without showing external signs of injury. In the latter 
cases the plants succumb quite suddenly, almost without 
warning. The leaves wilt, hang limp and flaccid, and in 
a few days the whole plant shrivels and dies. Even, 
though affected plants show little direct sign of the disease 
until the wilt sets in, they are often much dwarfed in size 
and produce fewer flowering branches than healthy plants. 
The fact that this disease may be present in apparently 
healthy asters, which only wilt after they come into flower, 
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