By: Bonnie L. Grant, Certified Urban Agriculturist
It’s not talcum powder and it’s not flour. That white chalky stuff on your plants is powdery mildew and it needs to be dealt with as the fungus spreads easily. Read on to learn how to get rid of powdery mildew on your indoor plants.
Powdery Mildew on Houseplants
Powdery mildew on houseplants is a fungal disease. Initially, it produces circular powdery white spots on the foliage of plants. As the disease spreads, the entire plant material can be affected with the fluffy white fungus. Over time parts of the plant will succumb to the disease and die. It is very contagious and, once one part is affected, it will infect the rest of the plant if not checked.
The fungus can affect plants outdoors, but indoor powdery mildew is more common due to conditions. The indoor powdery mildew requires temperatures around 70 F (21 C). It occurs when there is poor air circulation, low light, and unlike outdoor powdery mildew, thrives in drier conditions.
The mycelium formed from the fungal spores is the source of the fluffy stuff on the plant parts. The spores spread in the air and when water splashes on plants. Powdery mildew control is essential in the home due to this aggressive, contagious state.
How to Get Rid of Powdery Mildew
The white substance rubs off easily with your fingers or a cloth. Don’t mist plants. Prevent the foliage from getting wet when watering. Keep plants spaced to enhance air flow or use a small fan to circulate the air.
Once one plant shows signs of infection, isolate it to prevent the spread of the fungus. Pinch off the affected areas and discard. Common plants affected by indoor powdery mildew are:
- African violet
If powdery mildew on houseplants is present on all specimens and cultural control is not effective, advance to chemical control. Powdery mildew treatment indoors may be achieved with common household ingredients.
Water the plants well from under the foliage, then apply a spray of 1 tablespoon (5 mL.) baking soda, 1/2 teaspoon (3 mL.) liquid soap and 1 gallon (4 L.) of water. You may also add 1 tablespoon (5 mL.) of horticultural oil to help the mixture adhere to the fungus. Apply to the top and bottom of the foliage to get all the fungal areas. Using this powdery mildew control indoors is safe and non-toxic and effective on some, but not all, species of plants.
Another organic method to try is a milk spray. Use organic milk that is free of hormones and preservatives. Mix one part organic milk with nine parts water and spray once per week on all surfaces of the plant. Provide adequate ventilation while the spray dries on the foliage to prevent mold.
Fungicides for Powdery Mildew on Houseplants
When all else fails, use a household fungicide to kill the spores and prevent the spread of indoor powdery mildew. There is some risk of toxicity in any preparation you purchase so read the label carefully and apply as the product is intended. It’s best to apply any fungicidal spray outside to prevent drift of the particles in your home.
The use of neem oil as a fungicide for powdery mildew on houseplants can also be used.
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Read more about General Houseplant Care
Tomatoes, squash and zucchini are some of the easiest plants to grow in your summer garden, but they and other widely grown vegetable plants are subject to a pesky fungus called powdery mildew. Using hydrogen peroxide for powdery mildew is one way to rid your plants of this fungus.
Gary Pilarchik of the seed company Rusted Garden recommends mixing 3 percent hydrogen peroxide with water and spraying the solution onto the leaves of infected plants. He suggests mixing 12 tablespoons of hydrogen peroxide with a gallon of water. You need to dilute hydrogen peroxide because the concentrated solution could damage the leaves.
In the morning or evening, after you've harvested any ripe vegetables, spray the entire plant with hydrogen peroxide for powdery mildew. Spraying it once a day for three days should kill the fungus on plants. Then use a baking soda-sulfur spray solution once a week to prevent the fungus from returning.
Close up view of powdery mildew mycelium mat and spore producing bodies.
Elizabeth Bush, Virginia Polytechnic Institute and State University, www.forestryimages.org
In spring, as daytime temperatures rise above 60 °F, the fungi responsible for powdery mildew begin to produce spores (conidia), which are dispersed into the air. Infections occur when they contact a suitable host and environmental conditions are favorable. Initial symptoms are small, circular, powdery, white spots, which expand and eventually join as infections progress. Infections spread as spores produced in these white patches move by wind and splashing rain to other locations on the plant or nearby plants.
The fungus survives the winter attached to plant parts and plant debris, such as on fallen leaves. As weather warms in the spring, the process begins again.
Control and Prevention
How to Prevent Powdery Mildew
As with all pests and diseases, the best means of controlling powdery mildew is proactive prevention.
- Choose plants for your garden that are resistant to powdery mildew. Many mildew-resistant varieties of cucurbits (melons, cucumbers, squash, etc.) have been developed and can be bought from major seed suppliers.
- Plant in sunnier spots, as powdery mildew tends to develop more often in shady areas.
- Selectively prune overcrowded areas to increase air circulation around your plants this helps to reduce relative humidity.
- Watering from overhead can help to wash spores off leaves. Note, however, that wet foliage can often contribute to the development of other common diseases, so it’s best not to rely on this as a prevention tactic.
How to Control Powdery Mildew
- Consider spraying infected plants with protectant (preventative) fungicides. Effective organic fungicides for treating powdery mildew include sulfur, lime-sulfur, neem oil, and potassium bicarbonate. These are most effective when used prior to infection or when you first see signs of the disease.
- If you don’t want to use chemical fungicides, try spraying your plants with a bicarbonate solution:
- Mix 1 teaspoon baking soda in 1 quart of water. Spray plants thoroughly, as the solution will only kill fungus that it comes into contact with.
- Once plants are heavily infected, it’s very difficult to get rid of the disease, so focus on preventing it from spreading to other plants. Remove all infected foliage, stems, and fruit and destroy them, either by throwing them in the trash or by burning. Remember, do not compost any infected plant, as the disease can still be spread by the wind and persist in the composted materials.
Get Facility Proposal
There’s nothing good about powdery mildew, especially for an indoor home grower and their prized cannabis plants. Once you see the dreaded white powdery substance, you know there’s a big problem on your hands. And much work will be demanded of you because of it. Powdery mildew certainly doesn’t just go away if left ignored and untreated. And you can’t even see it before it’s too late! It is too small for the naked eye to see when spores are traveling through the air. Plus, once those subatomic powdery mildew spores fall onto a plant, the infection will be invisible for a few days. You can only see it a few days after it has infected your plant.
What can a home grower do to prevent powdery mildew? Home growers have various options to prevent it. Many cannabis cultivation books have a lot to say about the issue, but these four prevention strategies will help you avoid powdery mildew like the best of them.
1. First, hang an Airo Home Hobby in your grow tent or grow room to clean your air. Airo Home Hobby uses photocatalytic oxidation (PCO) to literally explode subatomic powdery mildew spores into nothing but water vapor and trace elements of CO2. They are safe and easy to use, and they don’t pull much electricity. Airo Home Hobby units use 100 watts. If you’re starting a new home grow, and have the budget to do it right from the beginning, putting the Airo Home Hobby to work in your grow is putting your best foot forward. The Airo Home Hobby units are a smaller version of the original AiroClean420 model for commercial cannabis farms. After several years of success in commercial cultivation, the company finally made available a smaller unit for small grow spaces. Don’t wait and get powdery mildew, get Airo Home Hobby and prevent powdery mildew like the professionals do!
2. Next, aim to keep your humidity lower than 55% RH in your grow room or grow tent. This will likely require you to sometimes use a dehumidifier, air conditioner, fans, etc. You can even use a controller to turn on your humidity-lowering mechanisms. For example, you can set it to turn the dehumidifier on every time it reaches 55% RH. Powdery mildew won’t be able to live in an environment with under 55% humidity, so always keep an eye on your humidity levels with at least one, if not two hygrometers.
3. Be sure to use safe foliar sprays to prevent and kill powdery mildew. You can try products like Trifecta Crop Control, Monterey’s Horticultural Oil, Neem Oil, Plant Therapy, Serenade, or Copper Fungicide. Rotate these products too. The best time to spray is before lights go on, or after lights go out. Follow the application instructions on the respective label. Some may recommend that you allow 4 hours of dry time, for example. If you need to spray at another time than before lights on or after lights go out, just do not apply your foliar sprays under the grow lights. That’s a rule that will prevent your plants from getting burned badly and cause other problems too. A once a week application of one of the above mentioned sprays is usually ideal.
4. Lastly, always clean your trim scissors and gardening tools with bleach. Alcohol will help sanitize, but bleach just does a better job.
Preventing powdery mildew and other fungal diseases is especially important to home growers who live in humid climates, but even dry areas get humid hot spells. Thankfully, preventing powdery mildew has become less burdensome due to AiroClean420 and Airo Home Hobby air purification machines. Run them in your indoor grow and you’ll be as prepared as you can possibly be. And you can also run the numbers if you’re thinking about the numbers!
To purchase a unit for your home grow, you may call an AiroClean420 representative at 1-844-247-3913 or visit https://www.airoclean420.com/airo-home-hobby-grow to order online. Payment plans are available. They include four equal payments of $254. Order today!
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Powdery mildew. Photo: Ann Whitman
A powdery white growth on leaves is the first evidence of this fungal disease, which affects beans, cucumbers, squash, pumpkins, lettuce, peas and many other kinds of plants. The fungus can spread to flowers and fruit. New growth and succulent plant tissues are particularly vulnerable to infection. Infected areas eventually turn yellow and dry up severe infection can weaken or even kill entire plants.
Unlike other fungal diseases, powdery mildew does not require wet foliage for infection to occur, although it does require high humidity. It can spread quickly in warm, dry climates. The fungus overwinters on plant debris.