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

                               KEY
                          1 = Symptoms
                           2 = Control

LETTUCE        

Aster yellows (mycoplasma)   
   1.  Yellowing, curling, twisting of inner leaves. Small brown
       spots. Heads poorly developed and soft or rot formed.  
   2.  Appears in August to September following leafhopper       
       prevalence.  Control leaf hoppers with insecticides. Control
       border weeds around garden, especially perennials. Aster   
       yellows has wide host range.

Drop (fungus)   Sclerotinia sclerotiorum or S. minor    
   1.  Starts as soft, water-soaked spot on stem near soil surface
       and spreads upward and downward. White cottony mass with embedded
       black fruiting bodies (sclerotia) on stem when in advanced stages.
   2.  Plant in well drained soil. Rotate crops. Avoid ground
       where cabbage or celery have been grown. Use Botran 2-3    
       lbs./100 gal. water after thinning. Rovral 1 1/2 lb./A. 

Downy mildew (fungus)   Bremia lactucae     
   1.  Symptoms appear on oldest leaves first. Spots begin as
       light-green areas on upper side of leaves. Soon followed by
       white mold on underside of leaf. Plants become yellowish and dwarfed.
       Fungus over winters in residues and in wild lettuce plants.   
   2.  Plant in well-drained soil. Apply foliar fungicide at 7-10
       day intervals after disease first appears. Use fixed or
       neutral coppers (caution should be observed as to leaf
       injury from coppers). Maneb 80 1 1/2 lb./A, or Maneb plus
       Zinc F4 1.2 qt./A, or Maneb 75 1 1/2 lb./A. 

Gray mold (fungus)   Botrytis cinerea    
   1.  Water-soaked discolored areas in lower leaves or stem.
       Entire plant may be rotted and covered with gray mold. A   
       slimy rot may proceed upward into head. 
   2.  Plant in well-drained soil.  Destroy infected plants. Remove
       infected refuse from area.  Same procedure as for Drop,    
       using Botran 2 2/3 lbs./100 gal. water.

Virus Diseases
Lettuce mosaic virus (LMV) and Cucumber mosaic virus (CMV)   
   1.  Leaves have green and yellow mottling. Dwarfing. Absence of heading. 
   2.  Destroy weed hosts, such as groundswell wild lettuce. Use
       mosaic-tested or mosaic-free seed. Insecticide program to
       control aphids.  Consult the Plant Disease Clinic for more
       information on serological testing for virus identification
       provided by Dr. Om Sehgal.