Practically any indoor garden or greenhouse can fall victim to powdery mildew, a fungal disease that manifests as white, powdery spots on leaves and stems. This happens when plants come in contact with spores of any ascomycete fungi, some of which develop faster than others. If spotted you need to begin treatment at the first sign of the fungus on your plants.
While powdery mildew is a relatively common problem for cultivators to deal with, it is anything but harmless. If left untreated, powdery mildew can damage and even kill your plants. If you submit your crops for purity testing any traces of the fungus could cause them to fail. It can spread rapidly so identifying the signs early is crucial to prevent an infestation.
Fortunately, there are effective ways control the fungus and a variety of strategies you can utilize to prevent an outbreak from occurring. Some important factors to consider are plant health, humidity levels and air flow. There are also a variety of products that can help combat the fungus, many are natural and pose no harm to the crops or the people that consume them.
Understanding Powdery Mildew
Identified as a white powder that appears on plant leaves as small, round clusters with a flour-like consistency. Once powdery mildew has taken hold of a plant, you’ll notice that leaves will become yellow and wilted. It can be harmful to digest or inhale so crops that are infected often should not be consumed or sold.
Powdery mildew thrives in warm environments with low air circulation and less than optimal humidity levels. The spores don’t require standing water to germinate so, unlike bud rot caused by Botrytis cinerea, powdery mildew can't be stopped by simply drying out the atmosphere. Even temporary, rapid fluctuations humidity levels are all that’s needed for spores to come to life.
Three things need to happen for powdery mildew to develop:
- Erysiphales spores need to attach to a plant’s surface
- Temperature of 70–80°F (22–27°C)
- Humidity levels: High relative humidity during the day (over 80 rh); Low relative humidity at night (under 40 rh)
Tips to Prevent Powdery Mildew:
As mentioned, powdery mildew is spread by fungal spores, so keeping those spores out of your grow room is your first line of defense. Cleanliness of the grow area should be a top priority. Reduce the risk of contamination by keeping any outside plants, tools or garden equipment from entering your facility. It is also important to keep yourself and anyone who enters your facility clean. Avoid coming from the outside and going straight into the garden without changing your clothing, removing your shoes, washing your hands, etc. to ensure that spores are not brought in from the outside.
Proper air circulation is another must. Any areas in your garden with poor air circulation is where the spore could begin to spread. Avoid crowding your plants to allow for proper air flow. Install fans so that air circulates evenly through the space and attach filters to any intakes to catch any spores or airborne debris that can potentially contaminate your crops.
Humidity is also an extremly important factor, yet this can be tricky for even the most seasoned cultivator. Large swings in humidity can be problematic. During the day when lights are on keeping the humidity under 80 can be a challenge. Dehumidifiers have become popular and are seem in most indoor grow rooms and greenhouses. At night, especially when the heat is on, it can be difficult to keep humidity above 40 and humidifiers could be needed to combat dry conditions. Environmental controllers with humidity sensors can track your humidity and turn humidifiers on/off as necessary to make sure you are keeping optimal humidity levels.
Often overlooked, the strength of your plants plays a key role in staying both pest and fungus free. Strong plants with strong cell walls will make you plants more resistant to powdery mildew. Adding Silica (Si) to your nutrient regiment has become increasingly popular to provide strong, sturdy plants that can ward of the fungus, disease and pests.
Ultraviolet (UV) Light, especially UVB light, can be highly beneficial for plants. It can increase growth, yield and quality. It will also help to improve resistance to pests and disease such as molds, mildews and fungus including powdery mildew. However, it's important to use UV light safely to avoid damaging plants or posing health risks to yourself or your staff.
Maintaining a proper Integrated Pest Management (IMP) regiment of preventative measures will lower the odds of having an outbreak of powdery mildew.
If you do have an outbreak realize that powdery mildew can spread rapidly and is very difficult to contain. Even after you think you have eliminated it, it can reappear. The fungus is airborne and can live without a plant to feed on for approx. 30 days. The best way to ensure it doesn't come back is to remove all plants from the facility, clean the walls, tray, tools and other equipment thoroughly with a cleaning product such as hydrogen peroxide. You can also clean the air, ducts and vents with chlorine dioxide.
Tips to Prevent & Eliminate Powdery Mildew:
Act Swiftly:- Prompt action is vital. As soon as you notice signs of powdery mildew isolate effected plants and immediately start treatment.
- Improve air circulation by using fans or and having proper intakes and outtakes.
- Trim affected leaves and stems to remove infected areas. Be sure to sanitize your pruning tools between each cut to prevent spreading the fungus.
- Solutions like a mix of water and neem oil, baking soda, or diluted milk sprayed on affected plants can inhibit the fungus's growth.
- Use specifically formulated fungicides to treat powdery mildew and follow all recommendations on the product's label.
- Ensure your indoor garden's environment is conducive to plant health. Keep temperatures moderate, maintain appropriate ventilation as well as humidity levels and avoid overcrowding plants.
- Regularly inspect your plants for signs of the fungus. Keep yourself and the environment clean to prevent infection.
- When selecting plants, opt for varieties known to be resistant to powdery mildew. Use proper nutrients and supplements to build sturdy plants with strong cell walls that are more prone to resists fungal disease.
Products to Prevent, Control & Eliminate Powdery Mildew:
As Powdery Mildew can be devastating to commercial cultivators, many products have come to market made to prevent & control, strengthen plants, clean, protect and eliminate the fungus. Here are a number of some products that can be used but by no means is it to be considered a complete list:
Prevent:GardnClean Slow Release, Certis Biologicals Double Nickel 55 / Double Nickel LC, GreenPlanet Nutrients Plant Guard, Procidic2, Bioworks SuffOil-X, BioSafe products
Control:
Athena IPM, BioSafe ZeroTol 2.0, BioSafe ZeroTol HC, BioWorks CEASE, BioWorks Milstop SP, BioWorks PERpose Plus, Certis Biologicals Sil-Matrix, Flying Skull Nuke Em, General Hydroponics TriShield, Grower’s Ally Crop Defender 3 / Fungicide, Lost Coast Plant Therapy, Marrone Bio Regalia CG, Scietetics Multi / Russet, Sierra Natural Science DC, Optic Foliar ATAK RTU
Neem Oil:EcoWorks EC 4-in-1, Certis Biologicals Trilogy
Silica:Power SI, Silicum, Agsil 16H, CES Bulletproof SI, Mills Vitalize, as well as many others. Silica can be derived from several sources and comes in different forms with different effects on your nutrient pH. See our full article on Silica HERE.
Clean:
GardnClean Fast / Liquid, Central Coast Green Cleaner, Ushio NaOClean Electrolyzed Water (E-Water) System, BioSafe products
Final Thoughts:
Preventing powdery mildew in a greenhouse or indoor garden requires vigilance and a multi-faceted approach. Even if you prioritize powdery mildew prevention, nothing is 100%. After prevention, your best line of defense is thorough inspection of your plants and, if detected, act fast to rid the fungus as quickly as possible.
By keeping a clean space for your plants, maintaining optimal growing conditions with a proper IMP program, growing strong, sturdy plants, promptly identifying and addressing powdery mildew and employing either natural or commercial remedies you will increase your odds of staying free from powdery mildew as well as other pests and fungal diseases.