http://www.cannabis.info/us/abc/30006965-bud-rot-and-powdery-mildew?q=us/abc/30006965-bud-rot-and-powdery-mildew The best way to avoid gray mold is to not give it a suitable home. Since the mold develops only in overly moist conditions, the first line of defense is controlling humidity to keep moisture levels under 50 percent. Gray mold and a hint of powdery mildew attack this sativa bud. Gray mold is likely to be most severe within the thickest part of the canopy, where air circulation is poorest. Thick outdoor plants can be spread with twine or netting to improve airflow. Remove interior and weak branches to improve circulation. Fans assist in mold prevention by removing pockets of high-humidity air surrounding the leaves and flowers. Don"t foliar feed plants during the last 30 days of flowering because moisture may become trapped inside the buds. Foliar feed early in the day during vegetative and early flowering so moisture on leaves or buds has a chance to dry before darkness. Watering the garden at the beginning of the light period or early in the day will give any excess moisture on the leaves an opportunity to evaporate. Cut out and remove the affected portions of the plant or bud, or remove it entirely to reduce potential host sites. Destroy any infected material, and sanitize any tools to prevent them from spreading infections. Moldy weed should be thrown out, although unaffected buds from the same plant may still be consumed. After removing all signs of infection, correct the environmental conditions. If circumstances do not allow the environment to be controlled, use preventive measures such as applying Bacillus subtilis (QST 713, known by the brand name Serenade), or a fungicide like Ed Rosenthal"s Zero Tolerance Herbal Fungicide, which includes potassium bicarbonate. Fungicides are more effective when used preventively, so apply at the beginning of the wet season. Some gardeners use sulfur to treat at-risk or infected plants. It can be applied as a powder, in sulfur dioxide mats, or from sulfur pots. Potassium bicarbonate prevents mold germination; sodium bicarbonate (baking soda) can be used as a substitute. Cinnamon, seaweed, D-limonene (citrus oil), and chamomile sprays have antifungal properties and will help control an outbreak. POWDERY MILDEW Powdery mildew (caused by several fungi) is the bane of modern marijuana growers. It looks like confectioner"s sugar dusting leaves. At first it appears as an irregular circle on just a small portion of the leaf. But it quickly spreads onto the surrounding tissue, covering the entire leaf. Colonies soon develop on the surrounding vegetation and in other areas of the garden. Powdery mildew is most likely to attack young leaves, up to two or three weeks old. The plant becomes infected when a spore, called a conidium, lands on a leaf and germinates. It soon grows an appressorium, a swollen structure that forms at the tip of a strand of hyphae that attaches it tightly to the leaf surface. Using the appressorium as a guide tube, the fungus pierces the plant"s cell wall and membrane and inserts a haustorium, a projection from the hyphae used to suck nutrients from inside the plant cell. The haustorium sucks up plant nutrients and sends them to the fungus, weakening the leaf and slowing growth. Within a week the fungus produces tiny mushroom stalks that release millions of spores, ready to infect more leaf surfaces. The fungus also produces another kind of structure, a cleistothecium, which contains spores. It overwinters outdoors and may also hide in a greenhouse or growroom after the crop has been harvested. The Fungi Powdery mildew spores-they are visible using a photographer"s loupe or hand microscopeThere are at least two different fungi that cause powdery mildew in cannabis. One of them, Leveillula taurica, is probably encountered in humid gardens. Sphaerotheca macularis is the more virulent organism. L. taurica is more likely to attack warm gardens. It prefers a temperature of about 25°C and can germinate in low humidity, but functions well in the 40 to 60 percent relative humidity usually found in indoor gardens. It is inhibited by moisture such as water spray, which destroys its spores. S. macularis prefers a cooler temperature, but the virulent race found in both indoor and outdoor gardens today is more tolerant of heat and bright light. It thrives in moderate humidity and its spores can live in water for short periods. In the unheated greenhouse and outdoors, the temperature preferences of both L. taurica and S. macularis overlap, so plants are susceptible from around 15°C to 30°C. They do quite well in moderate, rather than especially humid, weather. Spores of both species are airborne. When they land on suitable vegetation, they germinate, and start robbing the plant"s nutrients. The S. macularis spores also migrate with moving water such as drops of water falling from leaf to leaf, or blown by the wind to other plants. Controls Powdery mildew infections quickly spread. The whole garden is infected. Because of this pesky fungus" mode of transmission, it can be hard to prevent an outbreak, and it is challenging to control once an infection begins. It is in some ways more noxious than insect pests because it ruins any plant matter it touches, rendering it useless. However, infected buds can be processed for their contents to make concentrates such as water hash. Indoors, it is especially important to quarantine new plants before introducing them to the garden. Air filtration helps prevent powdery mildew from entering the room in the airstream. If there is any uncertainty about a location"s history with powdery mildew, sterilize the area and appliances before starting a new crop. An additional precaution for powdery mildew is to add UVC light to the garden. With ventilation, all incoming air should pass through the light. UVC light is germicidal, and delivers a fatal blow to all airborne fungal spores that pass under it. Once an indoor garden shows signs of powdery mildew infestation, there are many different approaches to eradicate it. If it is caught early, the gardener can prune away affected plant parts. It is important to disinfect tools used in the removal of infected plants and to carefully handle the pruned material in order to avoid accidently spreading spores. Powdery mildew is also controlled through close attention to temperature. Both types of fungi that cause powdery mildew are sensitive to heat and stop growing when temperatures range over 32°C. They quickly perish when the temperature rises to 38°C. Introducing a temperature spike to kill powdery mildew can be implemented, but if it is done improperly it could be detrimental to the plants. Fungi die in alkaline environments. Adjust the pH of the leaf surface so it is alkaline, with a pH over 8, using potassium/sodium bicarbonate or pH Up. This makes the leaf surface inhospitable for powdery mildew. Silica helps strengthen the stem, serves as an alkaline adjustor, and has natural fungicidal properties. There are many ways to increase silica in the soil or garden medium, such as adding diatomaceous earth, greensand, pyrophyllite clay, and high-silica fertilizers such as Pro-TeKt. Sulfur has also been used to control powdery mildew for centuries. There are formulations that are sprayed on leaves, and elemental sulfur can be used in burners to create sulfur dioxide. Sulfur is more effective at preventing the formation of powdery mildew than treating an infection. When used improperly or at too high a concentration, it causes leaf damage. Still, it is an effective control method. Foliar sprays can be bought or made to control powdery mildew. Make your own using cinnamon oil or tea, copper, garlic, herbal oils, hydrogen peroxide, D-limonene (citrus oil), milk, neem oil, and vinegar. Some gardeners recommend alternating these treatment options for best results. A spray of 10 percent milk to 90 percent water is also helpful in preventing spore germination. Some biological controls also work against powdery mildew. Serenade, when applied weekly, puts powdery mildew into remission. Another strain of bacteria, Bacillus pumilus (QST 2808, known by the brand name Sonata), produces a compound that disrupts fungal development. Sonata does not eradicate powdery mildew completely, but it works well in combination with Serenade or other solutions to greatly reduce an infection. Zero Tolerance Herbal Fungicide and Serenade work synergistically to combat powdery mildew and prevent its recurrence.