Vegetables - Disease Management          Pat Donald, MU  (573) 882-2716 
                                         Om Sehgal, MU (573) 882-7060

                               KEY
                          1 = Symptoms
                           2 = Control

SWEET POTATO        

Black rot (fungus)   Ceratostomella fimbriata 
   1.  Symptoms appear on foliage and on fleshy roots. Black
       cankers on underground stems. Leaves turn yellow. Circular,
       shallow brown spots on potatoes which may change to
       greenish-black to black. Shallow dry decay extends about to
       depth of vascular ring. Bitter taste. Fungus overwinters in
       diseased roots and in soil.  
   2.  Use clean plant beds. Use disease-free bedding stock. Crop
       rotation. Botran seed piece dip or bed spray. Destroy weeds:
       wild sweet potato, morning glory. Cure properly after harvest;
       do not wash.

Streptomyces Soil Rot or Pox (bacteria)   Streptomyces ipomoea    
   1.  Yellow and stunted plants. Destroys many of the lateral or
       fibrous roots. Brownish and sunken spots on potatoes       
       (smaller than black rot). Dried tissue later falls out,    
       leaving a pit or pox mark.    
   2.  Use clean, disease-free seed. Rotate crops. Keep pH below
       5.2, as the disease is more serious at higher pH readings.

Scurf (fungus)   Monilochaetes infuscans  
   1.  Superficial brown irregular discoloration on the root. Under
       storage, the potato may deteriorate more rapidly because of
       moisture loss.     
   2.  See Black rot.

Stem rot (several fungi)     
   1.  Plants become yellow and lower leaves drop off. Base of stem
       becomes dark. When split open, a brown or black layer is
       found under bark.    
   2.  Use clean disease-free plants or seed pieces (See Black rot).
       Use a three to four year crop rotation. Use resistant varieties.
       Consult seed catalogs for information on resistant varieties.

Post harvest decay (several fungi and bacteria)  
   1.  Mold growth and decay on potatoes. May penetrate if not controlled.  
   2.  Reduce harvest injuries as much as possible.  Cure properly.