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

below 60 percent, and keep the grow room clean! Use fresh, sterile growing medium for each crop.

    Botrytis, also known as bud mold, attacks both buds and stems of plants.

    Botrytis on this plant progressed from the bud down the stem.

This bud is covered with Botrytis. It was removed from the garden and destroyed.

Evaporated sulfur in a grow room or greenhouse stops Botrytis from contaminating plants.

Damping-off attacked this stem at the soil line, rotting the buried end of the stem.
    Cultural and physical control: As soon as Botrytis symptoms appear, use alcohol-sterilized pruners to remove Botrytis -infected buds at least one inch (3 cm) below the infected area. Some growers amputate two to four inches (5-10 cm) below damage to ensure removal. Do not let the bud or anything that touches it contaminate other buds and foliage. Remove from the garden and destroy. Wash your hands and tools after removing. Increase temperature to 80°F (26°C) and lower humidity to below 50 percent. Excessive nitrogen and phosphorus levels make foliage tender, so Botrytis can get a foothold. Make sure pH is around 6 to facilitate calcium uptake. Low light levels also encourage weak growth and gray mold attack. Avoid heavy crowding of plants and keep the light levels bright. Botrytis needs UV light to complete its life cycle; without UV light it cannot live. Some varieties seldom fall victim to gray mold. Many crosses are more resistant to gray mold than pure indica varieties. Harvest when resin glands are still translucent. Once glands turn amber, threat of gray mold increases substantially.
    Biological: Spray plants with Gliocladium roseum and Trichoderma species. Prevent damping-off with a soil application of Gliocladium and Trichoderma species. Hemp Diseases and Pests suggests to experiment with the yeasts Pichia guilliermondii and Candida oleophila or the bacterium Pseudomonas syringae.
    Sprays: Bordeaux mixture keeps early stages of Botrytis in check as long as it is present on the foliage. Preventive spraying is advised if in a high-risk area, but spraying buds near harvesttime is not advised. Seeds are protected from Botrytis with a coating of Captan. Check with your local nursery for product recommendations.
Damping-off
    Identify: This fungal condition, sometimes called Pythium wilt, is often found in soil and growing mediums. It prevents newly sprouted seeds from emerging, and attacks seedlings causing them to rot at the soil line, yellows foliage and rots older plants at soil line. It occassionally attacks rooting cuttings at the soil line, too. It is caused by different fungal species, including Botrytis, Pythium, and Fusarium. Once initiated, damping-off is fatal. At the onset of damping-off, the stem looses girth at the soil line, weakens, then grows dark, and finally fluid circulation is cut, killing the seedling or cutting.
    Control: Damping-off is caused by a combination of the following: (1) Fungi are already present in an unsterile rooting medium; (2) Overwatering and maintaining a soggy growing medium; (3) Excessive humidity. The disease can be avoided by controlling soil moisture. Overwatering is the biggest cause of damping-off and the key to prevention. Careful daily scrutiny of soil will ensure the proper amount of moisture is available to seeds or cuttings. Start seeds and root cuttings in a fast-draining, sterile coarse sand, rockwool, Oasis™, or Jiffy™ cubes, which are difficult to overwater. Do not place a humidity tent over sprouted seedlings–a tent can lead to excessive humidity and damping-off. Cuttings are less susceptible to damping-off and love a humidity tent to promote rooting. Keep germination temperatures between 70-85°F (21-29°C). Damping-off is inhibited by bright light; grow seedlings under the HID rather than fluorescent bulbs. Keep fertilization to a minimum during the first couple weeks of growth. Germinate seeds between clean, fresh paper towels and move seeds to soil once sprouted. Do not plant seeds too deeply, cover with soil the depth of the seed. Use fresh, sterile growing medium and clean pots to guard against harmful fungus in the soil.
    Biological: Apply Polygangron® (Pythium oligandrum) granules to soil and seed. Bak Pak® or Intercept® are applied to the soil and Deny® or Dagger®–forms of the bacterium Burkholderia cepacia– are put on the seeds. Epic®, Kodiac®, Quantum 4000®, Rhizo-Plus®, System 3®, and Serenade® also suppress many causes of