Excerpt from Jorge’s Book:
by Jorge Cervantes
Gray mold is the most common fungus that attacks indoor plants, and flourishes in moist temperate climates common to many grow rooms. Botrytis damage is compounded by humid (above 50percent) climates. It starts within the bud and is difficult to see at the onset– grayish-whitish to bluish-green in color – Botrytis appears hair-like and similar to laundry lint in moist climates.
As the disease progresses, the foliage turns somewhat slimy. Damage can also appear as dark, brownish spots on buds in less humid environments. Dry to the touch, Botrytis affected area often crumbles if rubbed. Gray mold attacks countless other crops, and air born e spores are present virtually everywhere.While most commonly found attacking dense and swelling flower buds, it also attacks stems, leaves, seeds and causes damping-off and decomposes dry, stored bud. It is also transmitted via seeds.
Watch for single leaves on the buds that mysteriously dry out. They could be the telltale signs of a Botrytis attack inside the bud. Constant observation,especially during the last two weeks before harvest, is necessary to keep this disease out of the garden. Flower buds are quickly reduced to slime in cool, humid conditions or unsmokable powder in warm, dry rooms. Botrytis can destroy an entire crop in 7-10days if left unchecked. Stem damage– Botrytis starts on stems and not buds– is less common indoors. First, stems turn yellow and cankerous growths develop. The damage causes growth above the wound to wilt and can cause stems to fold over. Transported by air,contaminated hands, and tools, gray mold spreads very quickly indoors,infecting an entire grow room in less than a week when conditions are right.
Minimize Botrytis attack incidence with low humidity (50 percent or less), ample air circulation, and ventilation. Grow varieties that do not produce heavy,tightly packed buds that provide a perfect place for this fungus to flourish. Cool(below 21 degrees C.), moist climates with humidity above 50 percent are perfect for rampant gray mold growth.Remove dead leaf stems, petioles, from stalks when removing damaged leaves to avoid Botrytis outbreaks, which often harbors on dead-rotting foliage. Increase ventilation and keep humidity below 60percent, and keep the grow room clean!Use fresh, sterile growing medium for each crop.
Cultural and physical:
As soon as Botrytis symptoms appear,use alcohol-sterilized pruners to remove Botrytis infected buds at least one inch below the infected area. Some growers amputate 2-4 inches below damage to ensure removal. Do not let the bud or anything that touch it contaminate other buds and foliage. Remove from the garden and destroy. Wash your hands and tools after removing. Increase temperature to 26 C. degrees 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 6to 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.
Spray plants with Gliocladiumroseumand Trichodermaspecies. Prevent damping-off with a soil application of Gliocladiumand Trichodermaspecies.Hemp Diseases and Pests suggests to experiment with the yeasts Pichiaguilliermondii and Candida leophila or the bacterium Pseudomonas syringae.
Bordeaux mixture keeps early stages of Botrytis in check as long as it is present on the foliage. Prevent active spraying is advised if in a high-risk area,but spraying buds near harvest time is not advised. Seeds are protected from Botrytis with a coating of Captan. Check with your local nursery for product recommendations.
This fungal condition, sometimes called Pythium wilt, is often found in soil and growing mediums. It prevents newly sprouted seeds from emerging, attacks seedlings causing them to rot at the soil line, yellows foliage and rots older plants at soil line, and occasionally attacks rooting cuttings at the soil line. 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.
Damping-off is caused by a combination of the following:
- Fungi is already present in anunsterile rooting medium
- Over watering and maintaining asoggy growing medium
- Excessive humidity.
The disease can be avoided by controlling soil moisture. Over watering 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, rock wool, Oasis TM or Jiffy™ cubes, which are difficult to over water. 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 21-29 C. degrees.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 of weeks of growth.Germinate seeds between clean, fresh paper towels and move seeds to soil once sprouted. Do not plant seeds too deep, cover with soil the depth of the seed. Use fresh, sterile growing medium and clean pots to guard against harmful fungus in the soil.
Apply Polygangron® (Pythiumoligandrum) granules to soil and seed.Bak Pak®, Intercept® are applied to the soil and Deny® or Dagger® – forms of the bacterium Burkholderiacepacia– are put on the seeds. Epic®, Kodiac®,Quantum 4000®, Rhizo-Plus®, System3®, 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.
Sometimes called false mildew, downy mildew affects vegetative and flowering plants. Young, succulent foliage is a favorite starting place. Powdery mildew develops in temperatures below 25degrees C.
It appears as whitish-yellow spots on top of leaves creating pale patches.Grayish my celium spawn is on leaf undersides, opposite the pale patches.Downy mildew can spread very quickly,causing a lack of vigor and slow growth;leaves yellow, die back, and drop. The disease is in the plant system and grows outward. It is often fatal, spreads quickly, and can wipe out a crop. Avoid promoting this disease by not crowding plants. Keep temperatures above 26degrees C and the humidity below 50percent.
Cleanliness! Use sterile growing medium. Remove and destroy affected plants not just foliage.
Apply Serenade®. Bordeaux mixture is also somewhat effective.
First indication of infection is small spots, on the top 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 dies 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.
Cleanliness! Prevent this mildew by avoiding cool, damp, humid, dim grow rooms and fluctuating temperatures and humidity. Low light levels and stale air mitigate this disease. Increase air circulation-ventilation and make sure light intensity is high. Space containers far enough apart so air freely flows in 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.
Apply Serenade® (Bacillus sub tiles) or spray with a saturation mix of baking soda and water.
Bordeaux mixture may keep this mold in check. A saturation of baking sodas pray dries to a fine order on the leaf;the baking soda changes the surface pH of the leaf to 7, and powdery mildew cannot grow.
For growing outdoors,the Durban variety is perhaps one of the most successful you can choose. This variety,originally from South Africa, also does very well in the European climate. Although this lady does need a little longer to complete her bloom, so you will need a bit of luck with the autumn weather, she is a great-looking weed with a terrific high!
What many growers do not know is that the Santa Maria strain was originally a proper outdoor variety, and that is why it often looks like she has the luxuriance and power to grow like a weed. There are even growers who swear that Santa Maria is one of the fastest growing marihuana varieties ever developed!
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