94 VEGETABLE GROWING IN NEW SOUTH WALES. 



The plants are attacked in all stages of growth. When young plants 

 are attacked early and severely they may be destroyed in a few weeks, The 

 severity varies with the season. In moist weather the disease may destroy 

 an entire crop. In ordinary weather it may take several months to cripple 

 the plants or destroy a crop. Infection takes place through wounds, but 

 more often through the water pores on the margins of the leaves. The 

 bacteria often commence development in the drops of water exuded by the 

 leaves, and then enter through the pores. They rapidly multiply and spread 

 through the veins of the leaves, and finally travel down the leaf stems and 

 the stem of the plant. The affected area of the leaf becomes dry and leathery, 

 and the veins have the appearance of black streaks. In the thick leaf stems 

 the black streaks may not show from the surface, but on cutting across or 

 along them the streaks will usually be seen. Often a part of a leaf or one 

 side of a plant only will be attacked, and the black streaks can then be 

 traced down the corresponding side of the leaf stalk and stem of the plant. 

 Dwarfing, one-sided growth, yellowing of foliage, gradual loss of leaves, and 

 brown streaks in the leaves, are the 9hief symptoms of the disease. The 

 gradual and successive shedding of the leaves often result in the production 

 of a long, dry stem with the conspicuous scars of the many cast-off leaves 

 upon it. 



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In ordinary weather, the picking off and burning of all affected leaves 



helps to check the disease ; but when the plants are about ready for market, 

 no time should be lost in harvesting them, as they will not keep. It has 

 been proved that the bacteria are capable of living for months (even a year) 

 on the surface of the seed, and that infection is spread in this way. 



The chief methods of prevention are : Disinfection of the seed for fifteen 

 minutes in a solution of formalin 1 part, water 250 parts ; or corrosive sub- 

 limate 1 part, water 1,000 parts. The latter is a very strong internal poison, 

 and must be handled with care. All insects should be kept down, to prevent 

 them spreading the disease, and if a field is infected, all refuse of old, 

 diseased plants should be collected and burnt not buried and a crop 

 rotation (see page 22) practised. 



Black Spot of Tomato. 



The " black spot " disease of the tomato is very common in New South 

 Wales, and probably no tomato disease causes greater loss. 



Black spot usually makes its appearance first at the flower end of the fruit 

 as a small brown discoloration. The discoloration spreads, and . the spot 

 becomes more distinct and definite in outline ; at the same time it becomes 

 depressed and darkens in colour. The larger spots, which may be an inch 

 or more across, have a dark-brown or black appearance, and are often 



