Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

entire process happens so fast that yellow, dead leaves dangle from branches. This disease starts in the plant’s xylem, the base of the fluid transport system. Plants wilt when fungi plug the fluid flow in plant tissue. Cut one of the main stems in two, and look for the telltale reddish-brown color.
    Control: Cleanliness! Use fresh, clean growing medium. Avoid nitrogen overfertilization.
    Preventive action is necessary. Keep nutrient solution below 75°F (24°C). Hydrogen peroxideinfusions will also arrest Fusarium. Always remove infested plants and destroy.
    Biological: Mycostop® (Streptomyces griseoviridis), or Deny®, or Dagger® (Burkholderia cepacia) and Trichoderma.
    Sprays: Treat seeds with chemical fungicides to eradicate the seed-borne infection. Chemical fungicides are not effective on foliage.
Green Algae
    Identify: Slimy green algae need nutrients, light, and a moist surface on which to grow. These algae are found growing on moist rockwool and other growing mediums exposed to light. They cause little damage but attract fungus gnats and other critters that damage roots. Once roots have lesions and abrasions, diseases enter easily.
    Control: Cover the moist rockwool and growing mediums to exclude light. Run an algaecide in the nutrient solution or water with an algaecide.
Powdery Mildew
    Identify: First indication of infection is small spots on the tops of leaves. At this point the disease has been inside the plant a week or more. Spots progress to a fine, pale, gray-white powdery coating on growing shoots, leaves, and stems. Powdery mildew is not always limited to the upper surface of foliage. Growth slows, leaves yellow, and plants die as the disease advances. Occasionally fatal indoors, this disease is at its worst when roots dry out and foliage is moist. Plants are infected for weeks before they show the first symptoms.

    Fusarium wilt causes the center of the stem to turn reddish-brown in color.
    Control: Cleanliness! Prevent this mildew by avoiding cool, damp, humid, dim grow room conditions, as well as fluctuating temperatures and humidity. Low light levels and stale air affect this disease. Increase air circulation and ventilation, and make sure light intensity is high. Space containers far enough apart so air freely flows between plants. Allow foliage to dry before turning off lights. Remove and destroy foliage more than 50 percent infected. Avoid excess nitrogen. Copper and sulfur-lime sprays are a good prophylactic.
    Biological Control: Apply Serenade® (Bacillus subtilis) or spray with a saturation mix of baking soda and water.
    Sprays: Bordeaux mixture may keep this mold in check. A saturation of baking soda spray dries to a fine powder on the leaf; the baking soda changes the surface pH of the leaf to 7, and powdery mildew cannot grow.
Root Rot
    Identify: Root rot fungi cause roots to turn from a healthy white to light brown. As the rot progresses, roots turn darker and darker brown. Leaf chlorosis is followed by wilting of the older leaves on the entire plant, and its growth slows. When severe, rot progresses up to the base of the plant stock, turning it dark. Root rot is most common when roots are deprived of oxygen and stand in un-aerated water. Soil pests that cut, suck, and chew roots create openings for rotting diseases to enter. Inspect roots with a 10X magnifying glass for signs of pest damage.
    Control: Cleanliness! Use fresh, sterile growing medium. Make sure calcium levels are adequate, and do not overfertilize with nitrogen. Keep pH above 6.5 in soil and about 6.0 in hydroponic mediums to lower disease occurrence. Control any insects, fungi, bacteria, etc., that eat roots.
    Biological: Binab®, Bio-Fungus®, RootShield®, Supresivit®, Trichopel® (Trichoderma harzianum), or SoilGuard® (Trichoderma virens).
    Sprays: Sprays are not effective.
Pythium Wilt/Rot
    Identify: (See “Damping Off.”)
Sooty Mold
    Identify: Black sooty mold is a surface fungusthat grows on sticky honeydew excreted by aphids, mealybugs, scale, whiteflies, etc. Sooty mold is only a problem on indoor plants when honeydew is present. Sooty mold restricts plant development, slows growth, and diminishes harvest.

Rotten roots have been soaking in stagnant nutrient solution. Foliage is very slow to grow when roots are rotten!
    Control: Remove insects that excrete honeydew. Once honeydew is controlled, mold dies. Wash away honeydew and mold with a biodegradable soapy solution. Rinse away soapy water a few hours