Problem: Fungi on your marijuana plants
Symptoms: Powdery, white or gray growth on leaves and tops (Botrytis), and wilting (root rot).
Solution: Fungus can causes the damping-off of marijuana seedlings, and this is usually the result of excessive humidity in the germination room. Marijuana growers living in climates with high humidity have another problem—mold—which can quickly ruin a crop either indoors or out. Particularly troublesome is Botrytis, also known as gray mold or bud mold. Botrytis attacks the entire plant (except the roots) but seems to favor the flowering tops and can turn them into a gray powder in a matter of seven to ten days if left alone. Don’t even think about using fungicides; instead, solve the problem mechanically. First, take care that your marijuana growing areas are clear of all debris and make sure your light intensity is as high as you can make it, including buying new bulbs if yours are more than a year old and are constantly used. Check your ventilation system and increase the air circulation by adding more fans and installing a dehumidifier. All you have to do is bring the humidity in your marijuana grow room or bloom room to below 50 percent, and that will prevent the fungus from growing and spreading by releasing spores.
Root rot (Phytophthora) is caused by spores growing on water-saturated roots. To counter this, make sure all plant growing media drains well and that container plants don’t sit in saucers full of water.
If you find mold on any of your live marijuana plants, be ruthless. Cut off all infected parts and destroy them by burning them in your fireplace, barbecue unit, or the firepit in your backyard. In addition to Botrytis, other molds can attack your plants, such as downy mildew and powdery mildew. The prevention is the same: cleanliness, air circulation, good ventilation, and humidity reduced to below 50 percent.