Diseases of Plants 299 



leaves, the plants may in a short time become almost 

 leafless. In such a condition the plants will produce 

 few or no fruits. 



In the center of the discolored spots, small dark dots 

 or pustules may be found. These are cistern-like cavities 

 in which countless spores are produced. Around the 

 spores is a material which when wet becomes jelly-like 

 and swells, pushing the spores in sticky clusters out of the 

 opening of the case. They will cling to insects and to 

 the hands of the gardener, and thus become distributed. 

 Rain may splash spores from leaf to leaf and from plant 

 to plant. Spores which fall to the ground will withstand 

 severe drying for at least three days, during which time 

 they may be blown about with the dust. Many gar- 

 deners quite naturally make the mistake of thinking 

 that the disease is caused by wet weather, but the wet 

 weather simply favors the spread of the parasite. 



Control of this disease is effected largely by preven- 

 tive measures. Clean soil should be used in flats and 

 cold frames in which seedlings are started. The spores 

 live over winter on stems and leaves of old plants ; hence 

 the dead remains of all tomato plants should be burned in 

 autumn. The spread of the disease can be checked by 

 spraying with Bordeaux mixture (4-4-50 formula) at 

 intervals of about 10 days, or more often during rainy 

 weather. At the first signs of this disease the gardener 

 should tie up plants to stakes, remove and burn the lower 

 and infected leaves which are wilting and showing 

 blotches, and then spray with Bordeaux mixture. All 

 this work, as well as that of cultivation, should be done 

 when the plants are dry. 



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