Department of Plant Pathology. 429 



the plum tree and burn them at once. They should be cut not only from your own 

 trees but from your neighbors. The wind carries the disease. Pick the old dry 

 " mummy " plums and peaches from the trees during the autumn or winter and 

 do not throw them on the ground. This is only wasting your time. The Brown 

 Rot fungus will mature its spores on these mummies on the ground as readily as 

 if they remained on the trees. Put the plums in a bag and carry them off and biirn 

 them. Gather up those that have already fallen to the ground and treat in the 

 same way. When picking peaches, always pick and destroy all rotten ones. This 

 is even more important than picking the healthy ones. The rotten potatoes, 

 turnips, cabbage, etc., from the cellar or store house should not be thrown back 

 on the fields or manure pile. They may be of some value as fertilizer but they 

 are dangerous to succeeding crops. Burn or bury them. 



Cultivation. The relation of cultivation to the control of plant disease is not 

 generally appreciated. In many diseases like potato scab, black rot of cabbage, 

 club root, etc., crop rotation is often the only means of eradicating the disease. 

 The careful and systematic destruction of weeds not only in the crop but along 

 the fences and road sides has a direct effect in keeping down certain fungi and 

 bacteria that live upon these weeds, as w-ell as on the cultivated crop. Often- 

 times weeds and grass serve to hold moisture in places where it will be favorable 

 to the development of certain diseases. This is strikingly true of the black rot of 

 grapes. The fungus is carried over in the old mummies that fall to the ground. 

 These lying among the weeds and grass that is often allowed to grow up beneath 

 the vines, find here a more or less constant supply of moisture throughout the sea- 

 son, enabling them to mature and scatter their spores to the lower leaves and fruits. 

 Keep the weeds and grass down by cultivation and the " mummies " are unable 

 to mature spores. Burying the diseased grapes by early plowing and scraping 

 from beneath the vines into the last furrow with a horse hoe is another practice 

 to be recommended. The time at which cultivation is done is sometimes an im- 

 portant factor. For example every bean grower knows that beans should not be 

 cultivated when wet. He does not usually know however, that this is due to the 

 fact that the spores of the fungus are scattered only when wet. From this it ap- 

 pears that intelligent cultivation must take into consideration the diseases with 

 which the crop is apt to be attacked. A knowledge of the conditions favoring the 

 parasite as well as of those needed by the crop will be essential. Know the crop 

 but know its diseases also. 



Seed selection 



It is well known that seed selection is one of the most important factors in main- 

 taining the vigor and productiveness of many crops. Its importance as a means 

 of controlling plant diseases becomes more evident every year. Evidence is con- 

 stantly accumulating w^hich indicates that many of our common diseases are 

 regularly and chiefly carried over from one season to the next in the seed. The 

 smuts of our cereal crops, the scab of potatoes (on tubers), the blight of peas, bean 

 blight and bean anthracnose are a few of the examples. In the case of some of 

 these seed selection as a means of eradicating the disease is not practical; in others 

 it seems to offer the easiest solution of the problem. Beans free from the anthrac- 

 nose fungus will apparently grow a clean crop. But the disease cannot always be 

 detected in the seed itself. You cannot sort out the diseased seed. You can how- 

 ever select pods that are free from the disease. Pods with no spots on them cod- 



