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

                               KEY
                          1 = Symptoms
                           2 = Control

CORN (Sweet)        

Helminthosporium leaf blight (fungus)   Exserohilum turcicum
Bipolaris maydis    
   1.  Northern:  Long elliptical lesions on leaf blades and ear
       sheaths. Lesions turn brown and dry. Leaves die prematurely.
       Southern:  Small, somewhat blunt lesions, confined by veins,
       on leaves and stalks of ears.  
   2.  Use three year crop rotation. Plow down or remove crop     
       residues.  Use hybrids with some resistance. Grower should 
       consult catalogs for current information on hybrids. If    
       serious, spray at 7-10 day intervals, starting when lesions 
       are abundant before silking. Use chlorothalonil (Bravo 500 
       1 1/8-2 3/4 pt./A, 720 3/4-2 pt./A, or 90 DG oz/8-1 1/2 lb/A 
       or W75 1 1/2-2 lb./A) or mancozeb (Dithane DF 1/2 lb./A,   
       Dithane F-45 1.2 qt./A, Dithane M-45 1 1/2 lb./A,
       Manzate 200 DF 1 1/2 lb./A, Penncozeb 1-1 1/2 lb./A,       
       Penncozeb DF 1-1 1/2 lb./A, Maneb 80 1 1/2 lb./A).

Seed decay  (several fungi)     
   1.  Seed rots or pre-emergence seedling death.   
   2.  Use treated seed.
      
Rust   Puccinia sorghi, Puccinia polysora
   1.  Pustules may appear on aboveground plant parts, but are most
       commonly found on the leaves.  Development of pustules on
       tops and/or bottoms of leaves help distinguish these two species.
   2.  Fungicides may be necessary especially when several dates of
       planting are present.  Penncozeb and Penncozeb DF 1 1/2-2
       lb./A, Dithane DF 1 1/2 lb./A, Manzate 200 DF 1 1/2 lb./A,
       Bravo 500 1 1/2-2 3/4 pt./A, 720 3/4-2 pt./A, 90DG 3/8-1 1/2 lb./A.

Common Smut (fungus)   Ustilago maydis     
   1.  Silver colored swellings or galls on leaves, stems, ears and
       tassels. Enlarge and turn black, breaking open and exposing
       abundant black spore masses.   
   2.  Remove galls before they break. Avoid using manure that is
       contaminated with smut (corn stalks and ears). Use
       smut-resistant hybrids. Use a three year crop rotation.

Stewart's wilt (bacterium)   Erwinia stewartii   
   1.  Plants stunt and wilt. Long pale green to yellow streaks in leaves
       that die and dry. Premature death of wilted plants. 
   2.  Control corn flea beetles early in season with approved
       insecticide. Start just at emergence and apply every 3-4
       days. Use wilt resistant hybrids. Grower should consult seed
       catalogs for current information on resistant varieties.

Maize dwarf mosaic virus
   1.  Symptoms are highly variable, but most frequent symptoms   
       seen are in the bases of the youngest leaves.  An irregular
       light and dark green mottle or mosaic pattern appears that
       may develop into light green or yellowish streaks along the
       veins.  A serological test is needed for positive identification.
   2.  Consult the Plant Diagnostic Lab for more information on   
       serological testing for virus identification confirmation provided
       by Dr. Om Sehgal.  This virus is transmitted by the greenbug
       (Rhopalosiphum maidis) and the green peach aphid (Myzus persicae). 
       Many grass species are reservoirs for this virus, but Johnsongrass
       is believed to be the major overwinter reservoir host for strains that
       attack this grass.

Wheat streak mosaic virus
   1.  Early symptoms appear as small chlorotic spots at the tips
       of young leaves.  The streaks develop parallel to the veins. 
       Symptoms vary with plant genotype.  Other hosts are wheat and grasses.
   2.  Consult the Plant Diagnostic Lab for more information on   
       serological testing for virus identification confirmation
       provided by Dr. Om Sehgal.  Avoid planting sweet corn where
       wheat was used as a cover crop and not completely killed   
       prior to corn planting.  The virus is transmitted by wheat
       curl mites which feed on wheat and other grasses.