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Common Fungal Diseases: Three Types To Look For [Part One]

July 1, 2016

As a system of biodiversity, professional cannabis gardens offer challenges. No matter how perfectly you set up your grow room and how much attention you give it, you will eventually find yourself up against a problem or two.

Most problems fall into three categories: pests, diseases and nutrient issues. There will usually be many factors that contribute to any issue you face. How you set up your garden and where you live can be a factor in disease. Heat, light, water and air movement should always be considered when diagnosing your plant’s problems, especially mildew and fungus. The biggest issues are powdery mildew (PM), bud rot and root rot.

Powdery mildew

PM starts as an airborne spore and infects not only your plants but can live dormant in your air system, on fan blades or on surfaces in your grow room. PM is an aggressive mold spore that, if left untreated, can ruin a garden.

Understanding signs and conditions: There are many ways that cannabis can be exposed to PM spores. For example, they can enter your ventilation system from outdoors. They can attach to your clothing, or a mouse or other pest can bring it in attached to its fur. Most commonly, you can bring it in from your clone supply without realizing it. In its early stages, PM appears as small white “fuzzy” spots on the fan leaves. Since the wind carries these spores, it becomes tricky to remove those leaves and plants with the fans on.

In moist areas, PM can show up when it rains and when the humidity fluctuates wildly. PM thrives in both very high and very low humidity, which makes it prevalent in many areas. The spores tend to bloom best when the humidity rises above 55% and the air is warm and stagnant. PM also thrives when there is little airflow. Leaf-to-leaf contact can create a situation that is perfect for growing the mildew; where the leaves touch each other and create moisture can be a starting point.

Preventing PM: Keeping your grow room clean before you see PM can help keep it out. Once you have an issue, cleaning everything thoroughly will help keep it from returning. Keep your plants well-thinned and available to much airflow. The ideal situation is to have much air movement throughout the whole plant from top to bottom and have a constant 40-50% humidity.

Dealing with PM: Once you discover a problem, it will be important that you treat it quickly and stop the cycle. Aggressive treatment toward your entire your system is necessary if you find PM. The first step is to turn off the fans and put on clean clothes, gloves and a mask. Enter the grow area and cut off all leaves that show signs of infestation. Take the infected leaves, buds and any part of the plant that has active powdery mildew growth and carefully put them in a bag that can be closed and removed.

After you have removed and trimmed all infected parts, it is time to apply a fungicide or other treatment to the plant. For the organic and natural grower, treatments will be varied and take some time, especially if your infestation comes during flowering. For the nonorganic grower, you will have more options for treatment. It is important to follow instructions when applying a fungicide or other treatment.

Don’t use fungicides that leave harmful residues that can give buds a peculiar taste after curing. There are also adverse health effects associated with smoking fungicide residue. The more you research the products you are interested in, the more quickly you will learn what works in your garden.


Bud rot (Botrytis)

Bud rot, also known as Botrytis (or gray mold), is a fast moving spore that takes advantage of poor environmental conditions. It is found virtually everywhere plants are grown. Bud rot can grow on many different sources of nutrients and survives well in the greenhouse. Bud rot is dangerous to both plants and cannabis customers.

Understanding signs and conditions: The infection starts near the stem and, by the time you are aware of it, the problem is usually out of hand. If conditions are right, once the spores have made contact you will see gray, green or white fuzz appear at the stem of the leaf at the stalk. From there, the rotting begins at the thickest buds from the inside out. You will notice what looks like graying or darkening to the point of sometimes looking purple, or buds finishing early. These symptoms are a sign you need to get out your handheld microscope and take a closer look.

Preventing bud rot: Prevention is key with bud rot. The first line of defense is to keep the system conditions healthy, clean and stable. Preventive treatments in the vegetative cycle can contribute to keeping the flowering cycle more maintainable. Also make sure your grow area is warm, dry and well-ventilated throughout the whole flowering cycle.

Dealing with bud rot: Remove the bud carefully in question and take it safely away from your grow area in a sealed bag. Break the bud open and inspect for gray, dark brown and even purple discoloration. Seeing this will be your indicator that you are dealing with bud rot. The infected buds will sometimes be arid and create a “dust” as you break open the bud for inspection; this is releasing more spores into the air. Hence, removing the bud from the grow room before the full examination will keep the rest of your plants protected.

Once you have determined you have bud rot, the only real treatment is total removal of the damaged areas. If you can salvage parts of the plant, you should. Isolate each rotting bud and carefully trim them away and into a bag. To minimize the potential for spores to spread while being cut and treated, cover the branches that are affected with plastic bags.

To prevent further contamination, make sure you clean your scissors and trimmers often. Unfortunately, if the plants are greatly affected, evaluate the possibility of just taking the whole plants down, to save the entire garden.

Root rot (Pythium)

Another devastating fungus is root rot, caused by the parasitic fungus Pythium that infects the roots of the cannabis plant. Root rot is most common in hydroponic or deep water culture (DWC) systems, but it can and will show up in soil.

Understanding signs and conditions: Root rot will quickly make your roots go slimy and smell like they are dying. In a hydroponics system, this can affect all the roots quickly. In soil, it can be a little bit harder to diagnose. But root rot can turn up quickly. Plants are most susceptible when they are already stressed by pests, other fungus or nutrient deficiencies. If you see plants that have quickly become wilted, brown leaf edges or yellow in color, you will want to investigate for Pythium.

Preventing root rot: Just like with all other fungus and pest problems, you will want to keep everything clean and keep the soil or growing medium clean and healthy.

Dealing with root rot: Whether root rot is in hydroponics, DWC systems or soil, the treatment is the same: remove the infection, and clean and treat with beneficial microbes. Using compost teas and a solution such as Rhizotonic in your grow medium can help fight root rot before and after infestation.


By Eric Stone
Image Credit: By Doc. RNDr. Josef Reischig, CSc. (Author’s archive) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
Cannabis Cultivation Today articles are for informational purposes only and should not be considered legal guidance or advice on grow practices. You should contact an attorney or a qualified cultivation consultant for specific compliance and cultivation advice.


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