Greenhouse & Indoor Gardening

Common Greenhouse Diseases & Controls

There are no quick cures for plants having disease. The best choices include taking preventative measures to keep your greenhouse clean and growing plant varieties that are resistant to any particular disease you are concerned about. Changing any of the climate factors – temperature, light and humidity, moisture level and plant location are all excellent ways to reduce and control disease.

Blossom end rot in tomatoes

Blossom End Rot

This is a tomato disease in which dark brown patch develops on the base of the tomatoes. It is generally caused by uneven watering.


  • Keep the growing medium wet but not soggy. Avoid splashing water on the leaves and fruit. Increase air circulation and lower the humidity level.


Botrytis appears as a fluffy gray or brown mold on leaves and stems of soft-leaved plants. It is associated with humid, cool weather conditions.


  • Remove all diseased areas, reduce watering and increase air movement.
  • Spray with GreenCure or Serenade.

Damping Off

Destructive fungi attack the roots and stems of seedlings causing rot. Seeds may decay in the soil and never germinate. Stems can rot at the surface and seedlings wilt and die. Roots can rot after the seedling has germinated and stunts it, then the plant dies. There is no cure.

Preventive Measures

  • Use only a sterile germination medium.
  • Sow seeds thinly.
  • Do not overwater.
  • Keep grow mediums at a recommended propagation temperature.

Downy Mildew

This is a gray, downy substance that generally appears on the underside of leaves of seedlings, lettuce and cinerarias.

Powdery Mildew

This is a white downy coating that appears on leaves and stems.


  • Remove badly affected plant parts.
  • Spray with bicarbonate of soda (2 tsp. to 1 liter of water).
  • Spray larger infestations with GreenCure or Serenade.
  • Improve ventilation.


Rust appears as small, raised spots on the underside of leaves. The spots can range from dark brown to light orange.


  • Remove affected leaves and destroy them.
  • Spray with GreenCure or Serenade.

Sooty Mold

This is a fungus that grows on the sticky honeydew excretions of many sap-sucking insects that appears as black, sticky substance on leaves.


  • Spray with soapy water.
  • Wipe with a damp cloth.
  • Spray with GreenCure or Serenade.
  • Eliminate the cause which is sucking insects such as aphids, mealybug, whiteflies.
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