DISEASES AND PESTS OF PLANTS. 21 



WATER-CORE. 



Like the last, this is a " physiological " disease, being the effect of a want of 

 balance or a disturbance in the functions of the tree not brought abour. by the action 

 of a parasite. It affects a wide range of varieties and is especially common in tne 

 Dry Belt. The tissue of a normal apple consists of minute cells filled with liquid 

 and numerous air-spaces between them. These latter make the tissue opaque. If 

 the pressure of sap becomes too great, liquid, instead of being confined to the cells 

 themselves, is also forced into the spaces normally filled with air. Such tissue has 

 a water-soaked and semi-transparent appearance. This is what has taken place in 

 " water-core." The watery tissue is at first in small spots adjoining the vascular 

 bundles or sap-channels, but later the core becomes filled with liquid. At this stage 

 the hard lining membrane of the core will be found to be broken, and is often covered 

 with a hairy growth. Affected fruit is generally exceptionally highly coloured. 

 Fruit on the south and south-west sides of the tree is generally most affected. Accord- 

 ing to recent investigations, the development of the trouble is due mainly to two 

 factors when the fruit is maturing : First, an excessive amount of sap in the tree, 

 such as may occur after a period of heavy precipitation ; and, secondly, a wide range 

 between the day and night temperature over a period of time. During the warmth 

 of the clay transpiration from the leaves is active, but this is checked at night more 

 rapidly than root-absorption is, with the result that the sap-pressure in the tree 

 becomes so great that the sap is forced into the intercellular spaces. The main 

 factors, therefore, are not under our control, except in so far as excessive sap-flow 

 may be due to too much irrigation. It has been found, however, that if fruit is 

 picked before the water-core has become too far advanced and placed in ordinary 

 cellar not cold storage, the excess of sap will be reabsorbed and the fruit become 

 normal. This does not apply to cases so far advanced that liquid has already 

 appeared in the core. A recent authority cites a case where 10,000 boxes of water- 

 cored apples grown in the Yakima District were removed from storage late in the 

 season with a loss of only 0.3 per cent. Since the disease may be present in the 

 apples from the south and south-west sides of a tree only, it would be well to deter- 

 mine if this is the case before commencing picking ; and, if so, the two sets of apples 

 should be kept separate. 



BEAN. 



ANTHRACNOSE (Colletotrichum lindemuthianum) . 



This disease attacks stems, leaves, and pods, but is most conspicuous on the last. 

 It is commonly known as "pod-spot." On the leaves itj appears as brown spots of 

 varying shape and size ; on the pods it forms sunken roundish spots of a dark-brown 

 or black colour. Two or more spots may coalesce to form large irregular areas. 

 Spores are produced in great numbers in spore-beds on the surface of the spots. The 

 spores are cemented together by mucilage forming a minute pink mass. When 

 wetted, e.g., by rain, the mucilage is dissolved and the spores set free. On the pod 

 the fungus often makes its way into the underlying seeds, which become infected. 

 Such seeds, if planted the following year, serve as the starting-point for the disease. 



Control. Use only seed gathered from pods free from 'the disease. Unless the 

 selection is made from such pods no subsequent hand-picking of the seed will ensure 

 that it is disease free, since seeds apparently sound may be sufficiently infected with 

 the fungus to spread the disease if planted. If the disease appears in the crop, work- 

 ing amongst the plants when they are wet should be avoided, since it is then that 

 the spores are freed. It should be possible to produce an unlimited quantity of clean 

 seed in the Dry Belt. 



Encyclopedia of Practical Horticulture, Vol. I., page 496. 



