VEGETABLE GROWING IN NEW SOUTH WALES. 99 



In districts where this disease occurs, it is found that by planting in the 

 warmer months the vines grow more vigorously and are less susceptible to 

 the disease. The sweet potato is a tropical plant, and the ground is 

 apparently not warm enough in the early spring to produce a sufficiently 

 rapid and vigorous growth. 



Downy Mildew of Cabbage and Cauliflower. 



This disease produces white to greyish, felt-like patches on the leaves and 

 stems. The destruction of all plant refuse, and the reduction of the amount 

 of moisture on the plant by the free access of air and light, will check the 

 disease, and spraying with Bordeaux mixture (see page 128) is recommended. 



Downy Mildew of Pumpkin, Melon, &c. 



This disease appears first in the form of spots upon the older leaves, near 

 the centre of the plant. The spots become more distinct and enlarged, 

 gradually encroaching on each other and forming large patches, The affected 

 leaves become pale and sickly, and soon shrivel up and die. The disease 

 progresses to the younger leaves, slowly in dry weather, but very rapidly in 

 warm, moist weather, and a field may soon be reduced to a mass of dead 

 leaves, as if killed by frost. 



After its appearance the disease is not readily checked; but by early 

 spraying with weak Bordeaux mixture (see page 128), it may be prevented 

 from commencing its infection. 



Downy Mildew or Onion Blight. 



The disease of onions referred to as blight, mildew or mould is caused by 

 a fungus. This disease is closely allied to the late (Irish) blight of the potato, 

 and resembles it in the rapidity of its spread through an infected field. It 

 may first be noted in a field in one or two definite areas, and recognised by 

 the leaves appearing, as if splashed with scalding water. 



During warm damp weather, the disease spreads rapidly and destruction is 

 complete. Examined in the early morning parts of the diseased leaves appear 

 a peculiar violet tint, due to the furry covering of mildew. The fungus lives 

 in the tissues of the leaves ; when weather conditions are favourable, spores 

 are given off which are readily scattered by wind and rain and are able to 

 infect a healthy leaf within an hour. Thus the area of infection is spread 

 at a remarkably rapid rate. 



Spores are able to remain dormant during the winter until favourable 

 conditions return in the spring, when germination takes place and the new 

 crop is infected. These spores pass the winter in the dead leaves left in the 

 field. If they could be destroyed at this stage the disease would not reappear. 

 The raking up and burning of all old leaves from a crop than has been 



