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Ministry of Agriculture, Food and Rural Affairs

Powdery Mildew

Powdery mildew (O. neolycopersici) symptoms on tomato leaf Powdery mildew symptoms on tomato leaf (O. neolycopersici) Powdery mildew of tomato (O. neolycopersici)
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Beginner

Scientific Name

Pseudoidium neolycopersici, Leveillula taurica

Identification
L. taurica

  • Initially, small light green to yellow patches appear on upper leaf surface of older leaves
  • Lesions may expand, become necrotic
  • Slight sporulation may be visible on lower leaf surface, or on both leaf surfaces if humidity is high
  • Entire leaves may die

P. neolycopersici

  • A white, powdery mold grows on the upper surface of leaves
  • The fungal growth is more dense than with L. taurica
  • Leaf yellowing, and eventually leaf death, may occur

Often Confused With
Leaf Mold


Period of Activity
Powdery mildew favours warm, humid conditions and fields under water stress. Leaf wetness is not required. Powdery mildew is much more common in high tunnel tomato production that it is in field tomato production.


Scouting Notes
Although this is an uncommon problem in tomatoes in Ontario, it can cause fairly severe symptoms.  Infected leaves quickly turn brown and shrivel up.

Advanced

Scientific Name

Pseudoidium neolycopersici, Leveillula taurica

Identification
L. taurica
Initially, small light green to yellow patches appear on the upper leaf surface of older leaves. Lesions may expand and become necrotic. Slight sporulation may be visible on lower leaf surfaces, or on both leaf surfaces if humidity is high. Entire leaves may die.


P. neolycopersici
A white, powdery mold grows on the upper surface of leaves. The fungal growth is more dense than with L. taurica. Leaf yellowing, and eventually leaf death, may occur.

Often Confused With
Leaf Mold


Biology
Both pathogens can infect solanaceous crops and some weed species. The spores can be carried by the wind.  Leaf wetness is not necessary for infection.


Period of Activity
Powdery mildew favours warm, humid conditions and fields under water stress. Powdery mildew is much more common in high tunnel tomato production that it is in field tomato production.


Scouting Notes
Although this is an uncommon problem in tomatoes in Ontario, it can cause fairly severe symptoms.  Infected leaves quickly turn brown and shrivel up.


Thresholds
None established.


Management Notes

  • A few fungicides are registered on field tomato for control or suppression of powdery mildew.