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

                               KEY
                          1 = Symptoms
                           2 = Control

POTATO (Irish)      

Seedpiece decay (several fungi)     
   1.  Rotted seed pieces, caused by Fusarium and other fungus
       species in the soil.  
   2.  Dip cut seed pieces into Mancozeb--Dithane M-45,
       Maneb 80, Maneb + Zinc F4, Manzate 200, Penncozeb or Penncozeb DF.

Bacterial ring rot (bacterial)   Corynebacterium sepidonicum  
   1.  Wilting in full grown plants with yellowing and upward
       rolling of leaf margins. Browning of vascular system in the
       stem. Discoloration in vascular ring of tuber.    
   2.  Use disease-free or certified seed. Do not plant any tubers
       with discolored vascular tissue. Sanitation of equipment and
       storage facilities. 

Black leg (bacteria)   Erwinia atroseptica 
   1.  Tops stunted, yellow and wilted. Leaflets are redish. Stem
       near ground line blackened.     
   2.  Plant uncut, B-sized certified or disease-free tubers only.
       Do not plant any tubers with discolored vascular tissue.
       Rotate crops. Use a Streptomycin seed piece treatment.

Early blight (fungus)   Alternaria solani   
   1.  Circular brown spots with concentric rings (targets) show
       first on lower leaves. Tuber infections can result in brown
       to purple, slightly sunken areas with raised well-defined borders.
   2.  Apply foliar fungicides at 7-10 day intervals, starting when
       plants are about 8 inches tall. Use Mancozeb--Dithane DF 1-2
       lb./A, Dithane F-45 .8-1.6 qt./A, Dithane M-45 1-2 lb./A,  
       Manzate 200 DF 1 lb./A, or Penncozeb DF, Penncozeb 1-2     
       lb./A or fixed copper, Bravo 500, 90 DG, 720, Maneb 80,    
       Maneb 75 1 1/2 lb./A, Maneb plus Zinc F4 1.2 qt./A or Rovral 1 lb./A.

Fusarium wilt (fungus)   Fusarium spp.  
   1.  Stunted plants and yellow lower leaves. Plants wilt and
       prematurely die. Browning of vascular tissue of lower stem and root. 
   2.  Plant certified disease-free tubers. Rotate crops.
       Use sanitation practices. 

Late blight (fungus)   Phytophthora infestans   
   1.  Leaves develop brownish to purplish black irregular lesions.
       Enlarge rapidly in cool, moist weather. White mold on lower
       leaf surface in moist weather. Whole plants can be blighted.
       Tuber infections and rots can occur.  
   2.  Plant disease-free tubers. Dust seed pieces with Mancozeb.
       Apply foliar fungicide at 5-10 day intervals. When late
       blight is present and/or cool and wet conditions persist,
       reduce interval to 3-5 days. Same fungicides as for early
       blight. Rovral for early blight only.  Ridomil MZ 58 1 1/2
       lb./A, Ridomil/Copper 70W 1 1/2-2 1/2 lb./A, Ridomil/Bravo
       81W 1 1/2 lb./A.

Black scurf (fungus)   Rhizoctonia solari  
   1.  Top growth stunted and with small aerial tubers. Brownish
       cankers at ground line.     
   2.  Plant certified, disease-free seed. Do not plant in cold soil.
         
Scab (bacteria)   Streptomyces scabies     
   1.  Tubers with rough, raised, corky, brown areas. They are    
       often circular and some may be pitted.   
   2.  Plant scab-free, resistant variety tubers in scab-free soil.
       Maintain soil at pH 5.2 or lower. See soil and seed
       treatment as for Rhizoctonia black scurf.

Soft rot (bacteria)   Erwinia carotovora  
   1.  Skin blotches on tubers. Soft, mushy rot of tubers. Fetid
       odor. Important disease in storage. 
   2.  Avoid wet soils. Keep tubers cool after harvest.  Prevent  
       injury to tubers during storage.

Verticillium wilt (fungus)   Verticillium spp    
   1.  Plants wilt during the day. Chlorosis and browning of leaf
       margins. Vascular browning of stems and tubers. May be
       difficult to differentiate from Fusarium wilt. Laboratory
       ID may be required.  
   2.  Use clean, disease-free, resistant variety seed potatoes.
       Use seed piece treatment program (see seed piece decay).   
       Follow four- to five-year rotation. Consult
       seed catalogs for current information on resistant varieties.

Viruses
Potato Virus X (PVX) Potato Virus Y (PVY)     
   1.  Many different symptoms, depends upon virus or virus
       combination. Mottled leaves with light and dark green areas.
       Curled and wrinkled.  
   2.  Plant only certified seed. Remove and destroy infected     
       plants. Control aphids with approved insecticides.  Consult 
       the Plant Disease Clinic for more information on serological 
       testing provided by Dr. Om Sehgal.

Leaf Roll Virus (LRV)    
   1.  Dwarfed plants stand stiffly. Leaves roll upward toward midrib.
       Leaves are crisp and papery, crackling when pressed together.
   2.  See Potato virus X and Potato virus Y.