354 DISEASES OF CROP-PLANTS 



Description. 



The affection is not a typical fruit rot. Though as much as 

 half the fruit may be collapsed and blackened the rest remains 

 sound unless affected by the secondary organisms which may 

 enter by way of the original injury. It appears first as a patch of 

 dark green water-soaked tissue at or near the blossom end of the 

 fruit, usually when this is one-half to two-thirds grown. The 

 patch darkens, becomes more distinct in appearance and definite 

 in outline and may remain small or spread until the distal half 

 of the fruit is covered. The affected part in a few days becomes 

 black and leathery, and usually more or less flattened or sunken. 



Causation. 



The disease has been the subject of much investigation, and 

 has been attributed by different authors to numerous fungus or 

 bacterial parasites. Several of these are liable to occur in the 

 later stages of the affection, and may extend its scope, con- 

 verting it into a real rot, but it is now coming to be generally 

 accepted that in its origin the affection is non-parasitic. Its 

 association with certain physical conditions, especially with 

 variations in water supply, has frequently been pointed out, and 

 C. Brooks published in 1914 the results of a wide range of studies 

 made to determine the influence of physical and chemical factors 

 on its prevalence. 



The disease is most severe on vigorous plants in a very active 

 state of growth, and a sudden check to the water supply of 

 plants in this condition is one of the most usual ways in which 

 the disease is induced, while Brooks has further shown that 

 continued excessive watering produces the same effect. Most 

 nitrogenous manures, and especially stable manure, increase its 

 incidence, and liberal applications may cause the losses to become 

 very heavy. Aeration of the soil decreases the tendency to the 

 disease, and lime has some effect in modifying the influence of 

 heavy watering. The evidence available gives no clear indication 

 of the actual nature of the disease, or even of the mode of opera- 

 tion of the factors which induce it, but recognition of these 

 factors provides, so far as they are under control, the means of 

 reducing its incidence. 



Control. 



Where the plants are artificially watered care must be taken to 

 make the supply regular but not excessive. With either natural 

 or artificial watering the drainage and aeration of the soil should 

 be as good as it can be made. The prevention of excessive 

 transpiration by shelter and light shade, the effect of which may 

 to some extent be obtained by close planting, have good results. 

 The soil may also be protected by trash of some description. 



In an instance coming within the writer's experience heavy 



