60 PROTECTION OF PLANTS, 1915-16 



Storage Rots of Potatoes. 



These rots may be caused by a variety of agents. A perfectly ripe 

 potato, if free from disease, is more likely to be a better keeper than an un- 

 ripe potato. What do we mean by a ripe potato? A ripe potato is one that 

 is in the best condition for digging. The time to dig potatoes depends 

 largely on individual conditions on the various farms. As a rule potatoes 

 on wet soils should be dug early, and on dry soils later, they should also 

 be dug later when the crop has been badly affected with disease, so as to 

 show the diseased tubers, so that when they are picked up the diseased 

 tubers may be removed and not put into storage to affect others. Where 

 the crop is not affected with disease it should be harvested as soon 

 as the tops die down naturally, or are killed by frost. Killing by frost 

 leads to another cause of Storage Rots; often when the potatoes are not 

 properly hilled, tubers near the surface will get touched with the frost and 

 these tubers when placed in storage will rot and spoil the others with which 

 they come in contact. Another cause of these storage rots is carelessness 

 in handling the crop. Where a potato digger is used the potato is often 

 badly cut by the digger. This is usually caused by not digging deep enough. 



Conditions of storage are often such that the numerous fungi and bac- 

 teria are placed in the very best of condition to thrive and infect the potato. 

 The starch of the potato is one of the very best of foods for these fungi 

 and bacteria. The cellar should be kept at a low temperature and not too 

 moist, if possible, a temperature not more than 40° F. is advisable; there 

 should be no superfluous moisture that will cause a moisture to settle on 

 the walls, and not too dry to cause evaporation from the potatoes. 



A few suggestions to remedy these conditions mentioned above are: — 

 Harvest when ripe, or if diseased just before frost, discard all diseased 

 tubers in the field, spray regularly your growing crop; take care not to dam- 

 agie tubers when digging; keep the cellars cool, below 40° F., and look over 

 the crop from time to time discarding all diseased tubers. 



Symptoms of some of the Common Diseases. 



The Late Blight is characterized by the spots on the leaf of a lighter 

 colour usually surrounded by a darker ring or water soaked area; on the 

 under side of the leaf there is a white powdery or downy appearance. This 

 spot may dry up and not do further damage, but in a warm moist summer 

 such as last, the spots will increase and in a very short time the whole 

 foliage of a field will be killed right down. This disease may be controlled 

 by spraying with Bordeaux. Early Blight which does not do a very great 



