Back to Diseases of cucurbits
Alternaria leaf blight
Alternaria leaf blight is caused by the fungus Alternaria cucumerina. This disease is most problematic on melon but can also occur on cucumber, pumpkin and squash. Alternaria leaf blight does not commonly infect fruit but can reduce yield and quality through reduced plant vigor and sunscald of exposed fruit.
- Mature leaves near the crown of the plant are often infected first.
- Leaf spots start as small brown spots, often with a yellow halo, and grow into irregular brown spots (up to 3/4").
- Leaf spots sometimes develop a target-like pattern of rings.
- Severely infected leaves turn brown, curl upward, wither and die.
- Fruit are not commonly infected but can suffer from sunscald due to leaf loss.
Alternaria cucumerina can be carried long distance on wind currents and can be spread within the field by splashing water. Wet rainy weather favors diseases, and damage can be very severe in warm, wet conditions. The fungus survives from season to season in plant debris.
- Rotate vegetables so 3 or more years go by before planting any member of the squash family in the same location.
- Use drip irrigation instead of overhead sprinklers if possible.
- Do not work in plants when wet.
- Remove and destroy infected plants at the end of the season in small gardens.
- In large fields till under crop residue at the end of the season.
- Several fungicides are registered for use against Alternaria Leaf Blight. Preventative sprays are effective but are only necessary in fields with a history of Alternaria Leaf Blight.
- Commercial growers should refer to the Midwest Vegetable Production Guide for specific fungicide recommendations.