Powdery Mildew

Erysiphe polygoni

 

Identification

  • Powdery Mildew is a foliar disease caused by a fungus
  • Found in warm-dry climates of the Western US
  • Can occur in all sugar beet growing areas of the US, but overwintering structures are temperature sensitive and short-lived, therefore the  disease is most common in areas with a temperate winter climate

 

Detection
  • Starts as small radiating, whitish, dusty mats on older leaves of the plant
  • Under ideal conditions, the foliage can be covered in a few days
  • Optimum temperatures is between 56° and 86° F
  • Growth is inhibited by free water on the foliage, so the spread is less under sprinklers
  • A field of heavily infected plants may take on a bluish cast

 

Cause of Damage
  • The foliar mildew covers the leaf and hinders the plants ability to conduct photosynthesis
  • Reduced photosynthesis reduces growth and sugar production
  • Reduction of sugar and tonnage may be up to 30%

 

Control
  • Resistant varieties
  • Fungicides and sulfur applications
  • If disease appears less then 5 weeks before harvest, a control may not be needed
  • Crop rotation is unimportant since the disease cannot overwinter in dead tissue