Lettuce – Downy Mildew

Key Points:

1. Downy mildew occurs worldwide
   and is a serious fungal disease of
   field and greenhouse lettuce

2. Lettuce downy mildew is caused
   by the fungus Bremia lactucae and usually occurs in Spring and Autumn

3. Primarily a foliar disease, lettuce downy mildew has a direct effect on
   yield and quality

4. Although yield losses in the field at harvest may be substantial, further losses may occur during transit or storage
5. Control measures include:
   • downy mildew resistant cultivars
   • cultural practices, such as:
     • A ‘lettuce-free’ period
     • Crop rotation
     • Destruction of weed hosts
     • Increasing space between plants
     • Early removal of crop debris
     • Irrigation management

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