106 VEGETABLE GROWING IN NEW SOUTH WALES. 



Pumpkin-leaf Oidium. 



This disease of pumpkins, squashes, and melons is caused by a white and 

 powdery or mealy fungus which blights the leaves, causing them to turn first 

 yellow, then brown, and finally to die. 



Where practicable burn or otherwise destroy affected material ; do not 

 plough it in ; practise a rotation of crops (see page 22). Do riot grow 

 pumpkins two years in succession OH the same land ; when possible, put 

 them on new land. Weak Bordeaux mixture (see page 1 28) is often beneficial 

 when applied as a spray. 



Rhizoctonia of Potato. 



It is quite common to find on the surface of tubers dark-brown lumps of 

 irregular shape and size, like small lumps of soil, but which become black 

 and show up distinctly in contrast to the potato skin when wetted. They 

 do not adhere very firmly to the skin, and can be scratched off with the 

 finger nail or easily rubbed off ; when removed they leave very little scar on 

 the skin. This condition is sometimes called black speck scab. Some- 

 times, however, the lumps may be found to be deeper in the tissues, and 

 even beneath the skin. The stem of young plants are often rotted round the 

 collar or beneath the soil. Some die from what appears to be a wet rot. 



Various other conditions have been found associated with this fungus, 

 such as a bunching or rosette appearance of the tops and small potatoes 

 formed on the stem above the seat of injury, and sometimes in the axils of 

 the leaves along the stem. Such unusual growths, however, may be caused 

 by many other conditions, and must not be taken as absolute indication 

 of the presence of rhizoctonia. 



Besides causing the death of plants, the fungus also produces a rotting of 

 the tubers. This typically consists of a dry brown rot, which extends 

 inward from the skin, and very much resembles the true rot produced by 

 late blight when bacteria are absent. This condition is common in Tas- 

 manian potatoes, and is known as brown rust. 



The remedy is selection of seed and the dipping of all seed before planting. 

 'The following treatment is recommended : 



Dip the tubers in hot formalin (2 pints 40 per cent, formalin in 30 gallons 

 of water) at 118-122 deg. Fah. for 2 minutes. Then place in a heap 6 to 8 

 inches high, cover with wet bags and leave them for an hour. Remove the 

 t>ags and allow the potatoes to dry. 



The seed is best treated in half-bushel lots in a sack. A thermometer and 

 ;amall boiler or tub of about 15 gallons capacity are required. 



Ripe Rot of Tomato. 



This disease usually appears when the fruit is ripe or nearly ripe. It is 

 due to a fungus, which may cause loss even after pulling, as the rot may 

 spread and affect fruit carried in contact with the diseased fruit in the case. 



