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Gray mold

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Quick facts

  • Gray mold is a disease caused by the fungus Botrytis cinerea. It is also called Botrytis blight. 

  • It can affect any part of a plant and is one of the most common diseases found among bedding plants.
  • The disease easily infects plants that are already damaged or beginning to die.
  • It spreads quickly and can cause extensive damage to healthy parts of plants.
  • It likes wet, crowded conditions.
  • The best way to prevent it is to space out plants so they have room to dry out after rain or watering.
  • Remove infected flowers and leaves and destroy or compost them.
  • Most plants can recover from gray mold when warm, dry conditions return.

How to identify gray mold damage

    Often called Botrytis blight, gray mold causes a dark brown to black blight of flowers, buds, leaves and stems. 

    brown and gray fuzz on leaf curled and dead looking against other green leaves
    Gray mold on tomato leaf
    • In high humidity, fluffy gray spores cover infected plant parts; the spores are light brown-gray on black stalks.
    • Flower petals are especially susceptible to infection by the gray mold fungus.
    • Brown spots may be seen on petals or the entire flower may turn brown.
    • As flowers age, they fall off onto healthy leaves below.
    • The gray mold fungus then infects the leaves.
    • Removal of rotted petals often reveals a brown, target-shaped spot on the leaf, which quickly grows to rot the entire leaf.
    • With high humidity, a cloud of fluffy gray spores forms on old infected leaves and petals. These spores are easily blown or splashed to new flowers to start the infection cycle all over again.

    How to prevent gray mold

    Moisture is one of the main causes of gray mold. The wetter your plants are, the more susceptible they are to becoming infected.

    • Gray mold can show up anytime wet weather occurs during the growing season.
    • Infections usually begin on weak, dying or wounded plant tissue.
    • Handle plants carefully when transplanting and pruning.
      • Gray mold usually attacks wounded plants, so avoid harming your plants.
      • Prune plants later in the day when they are dry.
    • For plants that need full sun, plant in a sunny location with good air movement.
    • Keep your plants dry.
      • Avoid overhead watering. 
      • Use drip irrigation or a soaker hose.
    • Don't water late in the day. Give your plants time to dry off after watering them.
    • Space your plants properly to encourage good air circulation. Allow adequate space between row plantings.
    • Remember to clean between your plants. Remove any debris, including cuttings and dead leaves.
    • Gray mold can also be found on stored bulbs of garlic and other plant bulbs. Good air flow in dry conditions can control this disease on bulbs.

    How to control gray mold

    bunch of raspberries still on the bush with several in the middle with gray fuzzy growth
    Gray mold on raspberries
    • Remove the infected plants in a paper bag and destroy them. 
    • Clean thoroughly between your plants so that the disease cannot infect your other plants.
    • When gray mold affects fruits and vegetables, regularly pick them to reduce it's spread.
    • Don't allow overripe or rotten fruits and vegetables to accumulate in your garden.
    • Cultural controls should be enough to control gray mold.
    • Fungicides are available, but be sure to use a product that is specific to treating gray mold and recommended for the plant you are treating.

    CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

    When treating fruits or vegetables, be sure that the plant you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.

      Michelle Grabowski, Extension educator and Angela Orshinsky, Extension plant pathologist

      Reviewed in 2018

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