By: Cindy Rea
Courtesy of Maximum Yield Magazine
They're everywhere! Millions of microscopic fungi spores float through the air we breathe searching for the right environment in which to settle down and grow.
Most of these primitive spores pose no threat to the human population, however some are allergens that can cause those susceptible individuals severe discomfort. Fungi play a very important role in the biodegradation of organic matter. The active fungi help with the decay process, which composts all organic material back to the earth.
Mold is a type of fungus. Other types of fungi include yeasts and mushrooms. Sometimes the term mildew is used, however they are alternative names to describe the same type of fungus. Mold's most important requirement for survival and multiplication is moisture.
There are a number of parasitic and opportunistic molds and mildews that affect the plant world. Under ideal conditions these insidious spores can take up residence on unsuspecting plants, reeking total havoc. Some species of fungi are so invasive they can wipe out an entire indoor crop in a matter of a few days.
Almost all indoor growers will encounter one of the powdery mildew fungi during their gardening experience. Although the fungi that cause powdery mildew are usually different on different plants, all of the powdery mildew diseases are similar in appearance. In most cases, prompt recognition and control can prevent severe damage to plants from powdery mildew diseases.
Powdery mildews are host specific -- they cannot survive without the proper host plant. Some varieties of powdery mildew will germinate only on lilac while others can only live on a rose. The fungus spores live on plant material and cannot sustain life on any other surface. Powdery mildew has not been shown to cause any threat to humans.
Powdery mildew occurs most commonly in areas where there is slow or nonexistent air circulation, high humidity, and daytime temperatures of 70-85° F. Overcrowded plants may become easy prey for the powdery mildew fungus to germinate and proliferate. Plants receiving high levels of nitrogen also tend to be good hosts for powdery mildew. Light discourages the growth of mildew, therefore, a well lit garden tends to encounter far less powdery mildew problems. Mildew can spread rapidly since the disease cycle can be completed in as little as 72 hours. It commonly takes seven to 10 days from the time of infection to the development of symptoms and secondary spore production.
Powdery mildews, as the name implies, often appear as a superficial white or gray powdery growth of fungus over the surface of leaves, stems, flowers, or fruit of affected plants. These patches may enlarge until they cover the entire leaf on one or both sides. Young foliage and shoots may be particularly susceptible. Leaf curling and twisting may be noted before the fungus is noticed. Severe powdery mildew infection will result in yellowed leaves, dried and brown leaves, and disfigured shoots and flowers. Although it usually is not a fatal disease to plants, powdery mildew, left uncontrolled, will prevent normal flowering on highly susceptible cultivars.
Prevention is always the best defense against molds and mildews. Indoor crops should be started from seed or carefully inspected cuttings. Molds quickly take hold and propagate. Even a few microscopic spores will multiply rapidly and may infest the garden. Use only sterile growing media and equipment to ensure spores aren't lying dormant waiting to take up residence in a newly planted garden. It is unadvisable to bring soil in from outdoors as it may contain fungi spores and a host of other soil-borne bacteria and diseases.
Good air flow and ventilation are essential in minimizing contamination as well as maintaining optimum humidity levels. Remember, moisture is the number one criteria for mold and mildew's survival. High humidity levels encourage molds to reproduce quickly and make annihilation of the intruding fungi much more difficult. An ideal growing environment will have a relative humidity of between 30 and 50%. A room consistently reaching levels over 50% humidity is a breeding ground for fungi and a host of other problems. Humidity levels can be easily monitored with an inexpensive humidistat. Simple oscillating fans strategically placed in the room will help ensure good air flow. A good exhaust fan will remove stale, moist air and replenish it with fresh, oxygen rich air.
Unfortunately, despite every precaution, there are always opportunities for these sinister microscopic nuisances to make their way to your grow room. They can hitch a ride on just about anything that enters the room and eek out an existence in a sheltered area where conditions are favourable. Before long the mold is visible on leaf surfaces and the garden is infested.
There are several options for powdery mildew elimination. Sometimes removing infected leaves or plants and adjusting humidity levels are sufficient measures to correct the problem. Fungicides are commonly used to achieve acceptable control. For best results with fungicides, spray programs must begin as soon as mildews are detected. Spray both sides of the leaves, stems and growing surface. Do not use sprays during the flowering cycle or during lights on time.
There are other non-systemic, organic based products available through indoor gardening shops and hydroponic retailers that are excellent for eliminating and controlling powdery mildew.
Gray mold rot (Botrytis blight) is another common fungus found living on both indoor and outdoor plants. The gray mold fungus is much more destructive to plants especially during the flowering cycle. If left unattended, gray mold can cause damping off of seedlings and fruit rot. It can also penetrate young buds and destroy flowers from within.
Botrytis will thrive in a humid atmosphere, however the spores of this fungus are quite adaptable, and are able to sustain life in a drier environment. Once moisture is delivered this mold will germinate and spread rapidly within a couple of hours.
Initially grey mold can appear as a grey cottony fluff on stems and leaves. As the disease progresses it may cause stems and flowers to appear water soaked and rotten. Grey/brown sores may appear on stems, causing plants to fall over. The fungus can spread quickly, wiping out an entire garden in less than a week. Often grey mold is not detected until it has caused severe damage. The first evidence of a problem may be flowers falling off or crumbling when touched.
Sanitation is an essential part of gray mold control. Fallen leaves and dead plant material should be removed from the growing area. Grey mold thrives on plant debris. Sterilizing pruning equipment and washing hands thoroughly after contact with infected plant material will help eliminate the spread of further contamination. And like powdery mildew, grey mold can be treated with fungicides.
Most molds and mildews are easily controlled following a few simple practices:
. Do not crowd plants.
. Adequately fertilize plants using a well balanced nutrient formula.
. Use a preventative plant wash prior to detection of any molds or mildews.
. Apply a fungicide at first evidence of mildew and repeat applications as necessary. Never apply during flowering cycle.
. Prune infected plants and discard mildewed leaves and flowers.
. Keep growing environment and equipment clean.
. Maintain humidity levels below 50%.
. Refrain from handling wet plants.
. Ensure plants are dry before lights go off.
With over 1.5 million fungal species looking for homes it is good practice to make the overall area an unwelcoming and inhospitable environment for any spores to settle in. Grow rooms should start off as clean and sterile as possible. Wipe down all of the walls, ceiling and floors with a fungicidal wash, disinfectant soap or bleach solution. An application of a fungus resistant paint on walls, ceiling and floor is a good idea. Areas around windows are most susceptible to some verities of mold, ensure they are kept clean and dry all year. Don't leave old draperies or upholstered furniture in the room. Dehumidifiers can be used when humidity levels reach worrisome levels.
Cleaning all equipment between each crop rotation will ensure new plants are not infected with some lingering fungal spores. Immediate attention to any disfiguration or discolouration of plants will help identify and resolve problems quickly.
Molds and mildews that attack plants can be quite destructive to crops. The fungi is isolated to plant material only. They cannot live without a host plant or on plant debris. Both powdery mildew and grey mold are not considered bothersome to humans or pets and do not infect other surfaces of the growroom.
Strong, well nourished plants will be most resistant to damage, even when molds or mildews appear. Quick intervention, at the first detection of a mold problem will further minimize the damage.
Keeping your garden healthy and pest free is much simpler under the right conditions. Plants will thrive and produce an abundance of hearty fruit and flowers.