176 Diseases of Truck Crops 



Root Knot 

 Caused by Heterodera radicicola (Greef) Mull. 



Root knot of sweet potatoes is commonly found in 

 the Southern States in light sandy soils. It is char- 

 acterized by small swellings on the lateral feeding 

 roots. For further description, see p. 49. 



Methods of Controlling Sweet Potato Diseases 



The grower in dealing with sweet potato diseases 

 has a fourfold problem. No amount of care will 

 suffice to keep down his losses from disease, unless 

 he handles the problem thoroughly, beginning with 

 the seed and continuing through the seed bed, the 

 field, and the storage house. No one method of 

 control will suffice alone; each phase must be dealt 

 with separately. 



Methods of Obtaining Seed Free from Disease. The 

 selection of clean seed from bins, while working suc- 

 cessfully with other crops, is not to be practiced in 

 the case of sweet potatoes, since much disease is 

 carried inside of the roots or in the dust which coats 

 them. Seed treatment should be preceded by seed 

 selection. The use of seconds for seed is not satis- 

 factory, since they may be the small roots produced 

 from diseased hills, and hence carriers of disease. 



The use of slips is very desirable, since in this case 

 a beginning is made with healthy cuttings from which 

 hills of slip seed are produced. These in turn are 

 healthy, since they are not hampered by disease 



