THE POTATO. 137 



East says that yield is correlated with flat shape of tuber, 

 number of haulms and length of growing season ; that round- 

 flat tubers are richest in starch ; that a netted skin is usually 

 associated with high quality ; and that heavy fruit production 

 is associated with small tuber formation. 



In South Africa much might be done by the selection of 

 heat-resistant strains. 



Diseases and Other Pests. — The potato is subject to 

 numerous diseases, and as it is a widely-grown and important 

 crop a considerable amount of attention has been focusscd on 

 these by phytopathologists. Among the more important 

 fungous and bacterial diseases in the Union are the following — 

 viz., Bacterial Wilt, or Vrot-pootje (Bacillus solanacearmn) , 

 Potato Scab (Actinomvces chromogenus), Early Blight 

 (Macrosporium solani) Late Blight (Phytopthora infestans), 

 Rhizoctonia Disease (Corticum vagum. var solani), Potato Rot 

 (Nectria solani), and Wart Disease (SyncJiitrium endobioti- 

 cum). The last-named has just lately been discovered by Mr. 

 Puttick in Natal." 



Internal Brown Fleck is often met with in the Union, 

 and at present the casual organism (if any) has not been 

 isolated. 



Remedial Measures. — A good system of crop rotation is 

 probably one of the best preventive measures, and the selec- 

 tion of resistant strains is an avenue which might be further 

 explored. 



It must be remembered that while a number of these 

 diseases is limited to a specific host, others have alternate 

 hosts — e.g., Macrosporium solani is also parasitic on Datura 

 stramonium (Stinkblaar), consequently, weed control is of 

 special importance. The use of disinfectants is growing in 

 South Africa, and, no doubt, assists materially in the control 

 of some of these diseases — e.g.. Scab. The potatoes are 

 soaked in a formalin solution, one pint to 30 gallons of water, 

 for one hour ; or two ounces of corrosive sublimate to 16 gal- 

 lons of water for thi'ee hours. Seed tubers should never be 

 cut before treating same for the prevention of scab. 



Spraying with fungicides to control vine diseases is at 

 present uncommon in the Union, but may become more 

 popular as farming becomes more intensive. Bordeaux Mix- 

 ture, together with lead arsenate or Paris Green is chiefly 

 used as a fungicide and insecticide. 



