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Tomato leaf mold

Quick facts

  • Tomato leaf mold is typically only an issue in greenhouse and high-tunnel tomatoes.
  • The disease is driven by high relative humidity (greater than 85%).
  • Foliage is often the only part of the plant directly infected. Infection will cause infected leaves to wither and die, indirectly affecting yield.
  • In severe cases, blossoms and fruit can also be infected, directly reducing yield.
  • Leaf mold is caused by the fungus Passalora fulva (previously called Fulvia fulva or Cladosporium fulvum).

How to tell tomato leaf mold from other issues

Two photos, side-by-side, one of the top side of a tomato leaf with yellow spots (left) and one one of the under side of a tomato leaf with fuzzy olive spots (right).
Discrete yellow spots on the upper side of the leaf and the corresponding olive spores on the underside.
  • The oldest leaves are infected first.
  • Pale greenish-yellow spots, usually less than 1/4 inch, with no definite margins, form on the upper sides of leaves.
  • Olive-green to brown velvety mold forms on the lower leaf surface below leaf spots.
  • Leaf spots grow together and turn brown. Leaves wither and die but often remain attached to the plant.
  • Infected blossoms turn black and fall off.
  • Fruit infections start as a smooth black irregular area on the stem end of the fruit. As the disease progresses, the infected area becomes sunken, dry and leathery.

Biology

Tomato plants in a high tunnel showing leaves with yellow discoloration and fuzzy olive spores.
Discrete areas of olive-colored spore due to tomato leaf mold

Leaf mold is caused by the fungus Passalora fulva (previously called Fulvia fulva or Cladosporium fulvum). It is not known to be pathogenic on any plant other than tomato. There are many races of P. fulva.

  • Spores of P. fulva can survive for 6 months to a year above ground at room temperature.

  • It is unknown if spores will survive on the surface of stakes, tools and high tunnel walls from one season to the next in Minnesota's climate.
    • The pathogen forms dark, hard resting structures within infected plant debris.
    • These structures will produce an abundance of new spores when exposed to air.
    • They are the most likely means for P. fulva to survive from one season to the next.
    • The leaf mold pathogen can survive on and in tomato seed and may be introduced to a new area by this route.
  • Spores of P. fulva can start an infection at a wide range of temperatures.
  • Relative humidity at or above 85% will favor severe leaf mold epidemics, but some disease can occur at humidity less than 85 %.
  • New spores form on the lower surface of infected leaves within 10 to 12 days. If humidity remains over 85%, these spores will infect new leaves.
  • Within the growing season, multiple generations of the pathogen can be completed.
  • It can spread from leaf to leaf and plant to plant by wind, rain/overhead irrigation, tools, workers and perhaps insects.

Managing tomato leaf mold in home gardens

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Managing tomato leaf mold on farms

Row of tomato plants, lower two thirds of plants have dead, brown leaves
Leaf death caused by severe leaf mold infection
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Authors: Marissa Schuh, horticulture IPM Extension educator, Anna Johnson, Michelle Grabowski and Angela Orshinsky

Reviewed by Natalie Hoidal, Extension educator

Reviewed in 2021

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