Marijuana Grower's Handbook
Page 49
PREVENTION
+ The best way to prevent algae is to deprive it of light. This is a safe, non-chemical method of prevention. Use black tubing, rather than clear or translucent to prevent light from coming into the lines. Use a black or opaque reservoir to hold your water and nutrients. Make sure the cover is light-tight. Potting containers should be opaque.
+ Everything should be light-proof. Rock wool cubes should also be covered. You can use landscape sun-block fabric, white-black plastic (white side up) or plastic rock wool cube covers made for the purpose.
CONTROL
+ The best method of algae control is to prevent the problem by excluding light. This should be the main emphasis in systems with algae problems. If you already have algae growing, clean the system and replace or cover light transmitting tubing and reservoirs with opaque materials.
+ These are some products you can use to control or prevent algae from attacking the system:
+ Hydrogen Peroxide (H2O2)—A ½ to 1% hydrogen peroxide solution stops algae and other organisms but must be used regularly. It should not be used with mycorrhizae because H2O2 kills both good and bad micro-organisms.
+ Colloidal silver—A solution of a few parts per million (ppm) colloidal silver prevents algae growth, and like H2O2 it kills all micro-organisms.
+ UVC light—This is considered a germicidal light and is often used to keep hot tubs, fish tanks and other water free from micro-organisms.
+ Grapefruit seed extract-—Grapefruit seed extract kills algae without harming plants. This method is used by water supply systems for keeping drinking water, fish ponds and lakes algae free.
+ Barley straw rafts are used for algae control in ponds, lakes and other waterways. They can also be placed in hydroponic reservoirs, yet have limited effectiveness.
GRAY MOLD AND BROWN MOLD (BOTRYTIS)
Gray mold, botrytis cinerea, is found almost everywhere and can cause disease on most plants, including marijuana. It causes damping off and stem canker and bud rot.
Gray mold is one of the most common fungal diseases that attack marijuana.
The fungus can germinate only on wet plant tissue when the temperature is between 55-70° F (13-21° C). This often happens in dry weather as dew accumulates on the leaves. Once it starts growing it can tolerate a wide range of humidity and temperatures but high humidity and cool temperatures help it thrive. Lowering the humidity often stops it from continuing to grow.
Gray mold, like most other fungi, enters and easily infects any part of a plant that is either wounded, damaged from pests and pruning, or beginning to die. Thus it is very important to sanitize pruning equipment between cuts.
Cuts and lesions are a normal part of plant life, so all plants are subject to attack when conditions are favorable to the mold. Unhealthy or shaded areas of plants or crevices in buds are ideal conditions for the mold. Spores travel mostly via wind and rain and even in tap water, but they can be brought into grow rooms on clothing and pets.
GRAY MOLD
Shaded areas of the plant that do not get a lot of light are usually infected first. Then the disease spreads quickly through growth and spores.
Gray mold does the greatest amount of damage during flowering. It attacks the flowering tops, leaves, and stalks. Seedlings and seeds can also be infected and killed.
The mold starts out whitish like powdery mildew, but then darkens to a smoky gray or brown color. It has a fuzzy appearance, and light to dark brown rot forms in the damaged tissue.
Leaves and buds yellow from being suffocated by the mold. In higher humidity, the gray mold leaves a brown slimy substance on the leaves and turns the bud to rot, especially when the tissue is dense late in flowering.
Stems with unhealed breaks can be infected with B. cinerea causing stem cankers, which then affect the rest of the plant by depriving it of nutrients and water.
PREVENTION
+ Indoors, avoid conditions favorable to the mold by controlling humidity and temperature. Brown mold can be considered an environmental disease created by excess moisture. Keep humidity under 50%. Water when your grow lights are on or during the day. Remove and discard dead or dying plant tissue. Make sure there is no moisture on leaves and buds when the lights go out. Gray mold indoors is usually caused by high humidity.
+ Outdoors, you can’t control the weather but you can prevent bud rot. Bacillus subtilis is a bacterium that attacks B. cinerea. It can be sprayed on the plant as a preventative. Several brands, including Serenade® are available
+ Potassium bicarbonate (KHCO3) and pH Up change the pH of the environment from alkaline to acidic. Alkaline environments inhibit the germination of molds and fungi including gray mold. There are many brands available.
+ Neem oil and sesame oil form a barrier and inhibit mold germination.
CONTROL
+ If you see the mold or stem wounds, apply a fungicide. The mold is particularly difficult to remove from plants in late flowering.
+ Removing the mold from living bud to prevent its spread may do more harm than good unless done carefully. The very act of fiddling with them may help transfer the mold to new sites. Sterilize tools by dipping them in alcohol or hydrogen peroxide after curing a bud.
+ Bacillus pumilus (beneficial bacteria)
+ Clove oil
+ Compost and compost tea
+ Copper
+ Coriander oil
+ Neem oil
+ Potassium bicarbonate
+ Pseudomonas (beneficial bacteria)
+ Quaternary amines
+ Sesame and fish oil
+ Sodium bicarbonate
+ Sulfur: spray, vaporizer, or burner
+ Trichoderma (beneficial fungi)
LEAF SEPTORIA
Leaf septoria is also known as yellow leaf spot. It is not common indoors but occasionally attacks marijuana grown outdoors. The fungus interferes with leaf processes, including photosynthesis, inhibiting a plant’s ability to thrive. Though it is not deadly, it can greatly reduce yield.
Origin: Two closely related fungi, Septoria cannabis and S. neocannabina, cause yellow leaf spot. Yellow leaf spot is a wet and cloudy warm weather infection. Warm water and rain trigger the release of spores from the storage structures so it usually appears mid to late season. Infections occur when the temperature is in the 60’s (15°-20° C), but the fungi grow faster and are more destructive as the temperature rises, with its ideal temperature just below 80° F (25° C).
The spots first appear on the lower leaves of the plant. The fungus may also attack the stem.
The spots can be yellow, white, or gray-brown. They may remain small and round, but usually grow larger in an irregular pattern. Spots sometimes have reddish-brown perimeters. The infected tissue eventually dies, dries out and falls off, resulting in holes in the leaves. Severe infections result in defoliation, with no leaves left on the bottom of the plant.
PREVENTION
+ The septoria fungi are specific but ubiquitous. Only two species attack cannabis. As a result, plants are more likely to be infected if there is marijuana, or perhaps hops, growing outdoors near the garden. The spores overwinter on fallen infected marijuana leaves and debris and spread in three ways: wind, water and walking, either by humans and animals. Indoors, plants are not likely to come in contact with the spores unless they are trekked in or there are infected outdoor plants nearby.
+ Outdoors, infections are most likely to occur in gardens and spaces where marijuana has been grown before. To lessen the likelihood of infection remove all residue from the previous garden and then spray the area with a fungicide. Clean and decontaminate all tools after working with infected plants. If possible plant the garden in a different space each year.
+ Try one ounce (0.75 ml per liter) mixed spices and herbs in one gallon of hot water, let brew and cool. Strain. The fungicide is ready to use. Ed Rosenthal's Zero Tolerance® Fungicide contains both herb and spice oils and potassium bicarbonate.
+ Compost tea
is an effective control of molds. Use it as a spray.
+ Copper has been used as a fungicide for more than 100 years. It is very effective. Many brands are available.
+ Neem oil
+ pH Up changes the pH of the leaf surface making it harder for the mold spores to germinate. Use a solution with a pH of 9.
+ Potassium bicarbonate is a fertilizer as well as a fungicide. Use a 1% solution to change the leaf surface pH to alkaline.
+ Sesame and fish oils destroy the molds and mold spores.
+ Sodium bicarbonate, baking soda, changes the pH of leaves but it contains sodium, which can harm leaves if it builds up. Potassium bicarbonate is preferred.
+ Sulfur
+ Trichoderma (beneficial fungi) These beneficial fungi attack all kinds of fungal pathogens. Brands include Plant-Shield, Rootshield, Trichodex and BioTrek.
POWDERY MILDEW
Powdery mildew is a fungal disease that affects a wide range of plants, composed of a wide variety of species. Each species of powdery mildew has a very limited host range, but are all characterized by an easily recognizable white or gray powdery growth. The races that attack hops also attack marijuana.
Mildew spores can be found everywhere. Powdery mildew is a common problem for both indoor and outdoor growers whenever the temperature and humidity fall into its favored range.
Mildew spores are ubiquitous and endemic. In areas where marijuana or hops is being grown, wind and air ventilation are the main vectors. Another major factor is contaminated cuttings. However, clothing, pets, and outdoor animals can also deliver spores to the garden.
Spores can remain dormant until triggered by environmental factors, which include a suitable host, adequate humidity, moderate temperatures, low light intensity and acidity.
Powdery mildew is most likely to attack young leaves, up to two or three weeks old. The infection spreads over the plant and spreads to other plants in the garden. It affects buds, stems, stalks, and leaves.
The first signs of an infection are raised humps on the upper leaf surfaces. Plant leaves look like they’ve been dusted with flour or confectionary sugar. At first it might appear on just a small portion of the leaf in an irregular circle pattern. It quickly spreads and soon the entire leaf is covered as if it had been powdered.
Infected plants prematurely yellow, brown, and eventually die. If untreated, black specks can arise in the white powdery mildew. Buds have a stale, moist smell and are coated with the white powdery-looking mildew substance that can’t be removed. Powdery mildew hinders photosynthesis, causing your harvest to cripple to little or no yield.
Infected buds and leaves are not acceptable for smoking.
PREVENTION
+ Powdery mildew in vegetative growth is easier to treat than in the later stages of flowering. Quarantine all new plants in a separate area where they can’t infect other plants. If your plants get infected during flowering, especially far into the flowering stage, the buds will eventually become infected.
+ Dip new acquisitions and cuttings in a solution of potassium bicarbonate and milk on a routine basis. Filter incoming air with a hepa filter to prevent spores from entering the room in the airstream.
+ A germicidal UVC light like the ones used in food handling kills airborne powdery mildew spores. Ionizers and ozone generators precipitate and inactivate spores, lessening the chances of infection.
+ As with other fungi, restrict humidity and spore production by not watering or foliar spraying at night or with lights off. Water plants when lights first come on or with at least five hours of remaining light time. Keep humidity in check; anything over 50% may trigger problems. Even so, powdery mildew may attack since it often thrives in fairly low humidity. Keep plants spaced apart to allow for maximum airflow.
POWDERY MILDEW, photo by Sean M.
+ Ampelomyces quisqualis (beneficial fungi) This is available under the brand name AQ-10
+ Bacillus pumilis (beneficial bacteria)
+ Bacillus subtilis (beneficial bacteria)
+ Compost tea
+ Herb and spice fungicidal oils
+ Milk is an effective fungicide. Milk should be used as 1 part milk to 5 parts of water.
+ Neem oil
+ Potassium bicarbonate
+ Sesame and fish oils
+ Sodium bicarbonate
CONTROL
+ Remove infected leaves from the grow room, this is critical. Carefully remove them without knocking spores into the air. Place a bag over infected leaves and tie it shut; then remove the leaves. Use a fungicide on wounded stems from which you’ve removed the leaves.
+ The following product list will work for indoor and outdoor plants.
+ Vinegar
+ Bacillus pumilis (beneficial bacteria)
+ Bacillus subtilis (beneficial bacteria)
+ Cinnamon Clove, Coriander Rosemary and Oregano oils and teas
+ Copper
+ Horticultural oils containing jojoba or cottonseed oil use 1 tablespoon per gallon (15 ml per 4 liters) of water
+ Milk
+ Neem oil
+ pH Up
+ Potassium bicarbonate
+ Sesame oil
+ Sodium bicarbonate
+ Sulfur
ROOT DISEASES
Every plant must have a healthy root system. Pathogens can attack and damage the roots of one plant, then rapidly infect other plants in the garden. Fusarium, Verticillium and Pythium are common and destructive root aggressors known to all growers, whether soil gardeners or hydroponicists.
FUSARIUM
Fusarium inhabits the soil. Fusarium fungi vary across many species and subspecies, and a given strain of the fungus targets only a few plant species. Several strains target cannabis. Fusarium is so devastating that the US government has developed special strains to target cannabis and coca as part of the “War on Drugs.” The coca strain has been released on coca plants in Colombia.
Different fusarium species produce somewhat different diseases in cannabis. These diseases, primarily fusarium wilt and fusarium root rot, present different symptoms but respond to similar prevention and control methods.
It is not commonly found in marijuana gardens. However residual spores are more common in soil where hemp was once grown or where it still grows as a weed. Growers using hydroponic systems or sterile or pasteurized planting mix seldom see it. Fusarium infections are most common in warm weather, but overall the frequency varies. Because it is soil-based and species-specific it may be extremely common in one area but rare in another where the soil is not infected.
Fusarium spores can remain dormant in soil for years, and infected soil is nearly impossible to disinfect. The fungus can also spread from seed taken from infected plants.
Damage from Fusarium wilt is most evident on the leaves and stems. Fusarium root rot affects the roots first, then the disease works its way up the stem.
Fusarium wilt initially appears as small, dark irregular spots on lower leaves, which quickly become chlorotic (yellow-brown). Leaf tips curl upward, and wilted leaves dry and hang on plants without falling off. Stems turn yellow, then brown, and finally collapse. In Fusarium wilt the roots show no outward symptoms if the diseased plant is pulled up.
Fusarium root rot begins below the soil line, turning the roots rotten and necrotic and giving them a characteristic red color. The first visible symptom usually appears as the rot works its way up the stem, producing a red-brown discoloration at the soil line. This discoloration may progress to swelling and the stem may split open. The plant soon begins to wilt, then collapses as the decay spreads up the stalk.
In both wilt and root rot the fungus spreads through plant cells and clogs the xylem vessels, inhibiting water and nutrient transport. This vascular clogging inside the plants causes the external symptoms of wilt and collapse. Infected plants usually die. Fusarium survives in the plant debris, so infected plant debris should not be buried, composted, or placed on uninfected soil.
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p; PREVENTION
+ If an outdoor Cannabis crop falls prey to Fusarium, that patch of ground can no longer be used to grow Cannabis at all, although other plants will do fine there. Likewise seeds produced by infected plants should not be used. The pathogen stays dormant on the seed and attacks the plant when the seedling emerges, causing damping off and likely killing it.
+ Avoid planting marijuana in the same ground for many years in a row. Even though none of the plants show symptoms, multiple successive plantings can cause the fungus to build up in the soil until it reaches destructive levels.
+ Certain soil types have been found to be less conducive to the growth of Fusarium than others. Clay soils have fungistatic properties due to their high pH. Loamy soils with healthy and diverse plant growth often harbor native microbes that suppress Fusarium. These soils do not stop the fungus, but they slow it down, and may be helpful in combination with other preventive measures.
+ Properly aged compost, and tea made from compost, help protect plants from all sorts of fungal infections.
+ Container gardening is one of the best ways to avoid Fusarium, because it gives the gardener complete control over the soil. If an area that would otherwise be ideal (weather, sun, etc.) is known to be infected with Fusarium then containers allow you to take advantage of the site’s strong points while avoiding the disease issues. In order to prevent Fusarium infections, use sterilized or pasteurized soil mixes and sterilized or new pots. Do not over-fertilize. Make sure the soil drains.
+ Mycorrhizae (beneficial fungi) help improve plants’ disease resistance.
+ Streptomyces griseoviridis, Bacillus pumilus, and Bacillus subtilis (all beneficial bacteria) or Gliocladium (beneficial fungus) can be applied as pretreatments for seeds, as a soil drench, or as a foliar spray.
+ Make sure the soil pH doesn’t get too low. Neutralize acidic soil with dolomite lime or greensand. Fertilizers enhanced with potassium and calcium can help fight off and prevent Fusarium, while excess nitrogen and phosphorous may make the disease worse.