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Basil downy mildew

Quick facts

  • Basil downy mildew can spread rapidly and result in complete yield loss.
  • Infection starts on lower leaves and moves up the plant.
  • The pathogen that causes basil downy mildew can transmit on seed, transplants or fresh leaves.
  • There are no resistant varieties of sweet basil available.
  • Monitor all seedlings and transplants closely for yellowing leaves and gray downy growth on the lower surface of the leaf.
  • Certain fungicides can protect plants from basil downy mildew.
Basil leaves with holes from basil downy mildew

Basil downy mildew was first officially identified in Minnesota in 2012. Under the right weather conditions, basil downy mildew can spread rapidly and result in complete yield loss.

Although Peronospora belbahrii, the pathogen that causes basil downy mildew, cannot survive Minnesota’s winters, it can return on infected seed or transplants or by windblown spores.

Identifying basil downy mildew symptoms

Basil leaves with spots from basil downy mildew
Early symptoms of basil downy mildew
  • Infection starts on lower leaves and moves up the plant.
  • Infected leaves first turn yellow in areas restricted by major veins. With time, the entire leaf turns yellow.
  • Irregular black spots appear on infected leaves as they age.
  • Fluffy gray spores grow on the underside of infected leaves.
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Preventing and managing the disease

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Michelle Grabowski, Extension educator

Reviewed in 2018

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