270 DISEASES OF TROPICAL PLANTS 



CH. 



after the harvesting of the crop to collect and burn the 

 debris and waste parts of the plants, thus destroying 

 great quantities of spores and mycelium. This pre- 

 caution is especially necessary where the field is used 

 repeatedly for the same crop. 



Headways, fence-rows, waste fields, etc., should be 

 kept free from debris and plants on which a disease 

 may thrive and be passed to the cultivated plants. A 

 single old and neglected tree may foster enough diseases 

 to seriously injure a large orchard, and a few stray 

 tobacco or tomato plants may serve as a nursery for a 

 host of diseases for the field and garden. Weeds and 

 many other wild plants, both native and introduced, are 

 frequently the carriers of the organisms of disease. Old 

 stumps and logs in newly-cleared ground are frequently 

 the finest of nurseries for fungi which attack coffee, 

 cacao, and many other plants. 



Rotation of Crops. Certain classes of diseases, 

 especially root and tuber troubles and diseases caused 

 by Fusariums and bacteria, live in the soil, sometimes 

 for many years. When such diseases become destructive, 

 a new field should be selected for the crop, and a crop 

 of an entirely different character placed in the old field, 

 thus removing the host plant and allowing the disease 

 organisms to perish for want of satisfactory nourishment. 



Stock Feeding. The spores of certain organisms of 

 disease will pass through the digestive tract of an 

 animal and then grow. Therefore, when the host plant 

 is used for stock feed and the animals allowed to run at 

 large or the manure used on the fields which are 

 intended for this same crop, the animals involuntarily 

 become the disseminators of the disease. The manure 

 containing these spores may also be carried on the 

 wheels of wagons and farm implements, and on the 

 feet of labourers. Such manure should be used on 

 fields intended for crops of an entirely different char- 

 acter. Corn smut and rots of various kinds which are 

 prevalent on fleshy roots and fruits are frequently 

 scattered by these methods. 



