Fatal fungi

By Karen E. Szabo

All the time and money invested into growing the perfect harvest can easily be destroyed if telltale signs are ignored or simply not known. The most common crop killer is bud mold or gray mold, scientifically known as Botrytis cinerea. Coming in second to bud mold is Sphaerotheca macularis, more commonly referred to as powdery mildew. With proper preventative care, diligent crop inspections, and rapid treatment when problems arise, you can protect your valuable crops from these rapid killers.

Since bud mold is virtually undetectable in the early stages it is exceptionally dangerous. Bud mold attacks from the inside out and travels rapidly, allowing it to quickly spread throughout the entire surface of the plant without detection if you’re not constantly on the lookout for the symptoms.

Moisture lock is the number one cause of bud mold. The importance of keeping humidity low and maintaining sufficient air flow cannot be stressed enough; this will greatly reduce the risk of getting this fatal fungi. Bud mold can occur during both the flowering and drying stages of a harvest. In the flowering stage, bud mold infests the plant near the flower at stem level. During the curing process it is imperative to dry plants in a dark, well-ventilated area.

Bud mold can affect every part of the Cannabis plant, except the roots. A distinctive characteristic of bud mold is a change in smell, giving the Cannabis a musty or unpleasant odor. Sometimes mold spores resemble the appearance of trichomes, leading the grower to believe they have a Cannabis strain of higher grade than what they actually have. The best way to detect bud mold is to place the plants under a blacklight where mold spores will have distinctive green hue.

A wise investment for any grower is a pair of loupes. Checking for mold is only one of the numerous reasons they’ll be needed, so it’s a good idea to have them on hand to use for close inspection. Many different styles and various strengths are available in local grow stores or online. Look closely for black or dark green spots, white and/or grayish stringy matter or any other unusual coloring. Because bud mold grows from the inside out, it tends to stay hidden in the dense, often well-developed part of the Cannabis buds. It is very important to get to know your grow and familiarize yourself with its characteristics. Keep an eye out for yellowing, browning, withering or drying out of small leaves protruding from the kolas. If sudden color changes are noticed in these leaves, give them a firm pull; if the whole leaf comes away quite easily with the stem, most likely your plant has bud mold and corrective measures need to be taken.

Treating bud mold requires immediate attention. Proper treatment can be quite difficult and time consuming, which is not helpful when an outbreak is detected. Once every bud has been closely inspected, it is imperative to remove all infected areas immediately.  Sterilize your pruning shears in alcohol and cut the bud at least one inch below the affected area. Be careful not to spread mold spores during the removal process. Use caution not to touch any part of the uninfected harvest with your hands, clothing, scissors or anything else that might have come in contact with the infected buds. Simply disposing of the moldy buds is not sufficient to prevent reinfection. Immediately remove all infected buds from the home or garden area and destroy them. Also, remove all debris from the floor, as everything holds mold spores. Once removal is complete, be sure to re-sterilize your shears, as well as your hands. Immediately remove clothing and wash in hot water with a mild detergent.

To survive, mold needs at least 15 percent moisture. Preventive care is an easy measure to follow when compared to the potential disaster bud mold can cause. Unfortunately, mold spores are nearly impossible to eliminate completely due to varying moisture levels. If you run a sealed grow room, using a dehumidifier is an ideal way to reduce moisture and lower the humidity level. Be sure to empty it when full or it will not be of any use. It is critical to maintain the humidity level as low as possible, ideally between 35 and 50 percent, depending on flower stage. Do not allow the room temperature to fall below 70 degrees. Using oscillating fans to maintain air flow directly through the plants’ foliage not only strengthens the stems, but also helps in preventing the development of moisture pockets. Overcrowding locks in moisture; pruning the lower parts of the plants when necessary will help in reducing high humidity levels. For a more in-depth explanation of humidity and temperature requirements throughout the growing cycle, check out the accompanying article, Climate Control.

Foliar sprays can also be used as a preventive measure in protecting plants against bud mold. Local grow stores offer chemical-based, organic or non-organic sprays. Be sure to know what is in the product used. Certain products can be used only during specific stages of growth. For instance, chemical or copper-/sulfur-based sprays can be used only during the vegetation stage. Biological-based foliar sprays that contain Gliocladium and Trichoderma, or products that contain Bacillus subtilis, can be used to prevent and treat mold outbreaks up until harvest time.

The second most common crop killer is powdery mildew, Sphaerotheca macularis. Affecting only the leaves, powdery mildew can and will, without a fungicide treatment, spread very quickly. It has the potential to kill the entire harvest. Powdery mildew will appear, just as its name suggests, as a white, powdery substance on the plants’ leaves. The first signs of powdery mildew are small, circular white spots on the leaves. As it progresses, the mildew will become more prominent and, eventually, cover the entire surface of the leaf.  Powdery mildew can appear at any stage of growth. Bud mold and powdery mildew are both caused by excess moisture. Once identified, powdery mildew, as with bud mold, requires removal of all affected parts of the plant to prevent spores from spreading.

Not all is lost if it appears during the last few weeks of flower, however. It is possible to control powdery mildew with a good fungicide without affecting a scheduled harvest. When purchasing a fungicide for powdery mildew, it is important to consider the following: plant tolerance — be certain that it is not harmful to flowering buds; that it is effective for treating infestation; that it can be used as a preventive measure; and finally, that it is nontoxic and environmentally friendly. Fungicides to avoid contain sulfur, copper or neem oil, or are synthetic. Using preventive measures such as spraying mother plants and clones with fungicide will reduce the ability for mildew to grow.

As a precautionary note, powdery mildew doesn’t like sodium bicarbonate. Two to three tablespoons of it — NaHCO3, commonly known as baking soda — per gallon of water sprayed onto affected areas will help greatly. Use caution not to overdo it, as the extra sodium is not good for the plants. Sodium bicarbonate changes the pH at the leaf surface and draws water from the fungus, both of which are not appreciated by the pathogen.

Controlling and minimizing mold and mildew spores between grows is essential to a healthy harvest. Once the harvest is removed from the grow room, remove everything else from the room and wipe down with a 5 percent bleach and water solution. Thoroughly clean all walls, ceiling and floors, as well as anything that’s stationary in the room. Once dried, put everything back into place. For an extra measure that ensures the eradication of any remaining mold or mildew spores, treat the room with a high dose of ozone.

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