Damping-off

Marijuana Horticulture

by Jorge Cervantes

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 the soil line. It occasionally 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 loses 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: Fungi are already present in an unsterile rooting medium; Overwatering and maintaining a soggy growing medium; 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 and 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 70-85F. 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 Polygangrn (Pythium aligandrum) 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 Seranade also suppress many causes of damping off.

Chemical

Dust the seeds with Captan. Avoid benomyl fungicide soil drench because it kills beneficial organisms.