If you have leafy green vegetables or flowers in your garden, you probably have noticed a white powdery substance on your plants’ leaves, stems, or fruits during the warm seasons of the year. That’s powdery mildew. It may look terrible aesthetically and can spread very fast, but it’s nothing to worry about. It’s controllable and can be prevented quite easily.
What Is Powdery Mildew?
Powdery mildew is a whitish or greyish powdery substance that is often confused with downy mildew or the natural patterns on leaves of certain plants. The powdery look is because of the spores and mycelia (fungal threads) combined. It may not be as harmful, but it can leave a plant relatively impoverished as it feeds on the nutrients and water from the plant.
The fungi have many variations depending on the stage it’s in. the most common variations are Podospaera which affects roses, and Golovinomyces that attack cucurbits.
Difference Between Powdery and Downy Mildew
Compared to downy mildew, the two fungi share several similarities, but there are a few notable differences. Downy mildew appears only on the underside of the leaf, while powdery mildew appears on both sides. Downy mildew is more prevalent during the cold and wet seasons and is stopped by the sunny and hot seasons. Powdery mildew, on the other hand, appears during the hot and dry seasons. It’s also important to note that downy mildew has a darker color shade than powdery mildew.
How Does Powdery Mildew Cause Problems To Plants?
Under the right conditions, powdery mildew will spread fast and wide among the plants and, if left unchecked, could result in the death of leaves, stems and fruits. The fungi absorb water and nutrients from the plant, leaving it deprived of these critical requirements.
While the fungal thread is growing on the leaf surface, the mildew sends out specialized structures that live within the plant cells, eventually siphoning all the nutrients available. These root-like structures are called haustoria. Unlike pathogens such as Anthracnose and white mould, which tend to attack many plant species, powdery mildew is very host-specific, meaning it can only assault certain types of plants. That makes it easy to prevent and, in severe cases, control the fungi.
Conditions That Support The Spread Of Powdery Mildew
The fungi can be found practically anywhere. However, it thrives in areas with prolonged seasons of hot and dry weather. This does not mean that the fungi grow without water. It needs a certain level of humidity to flourish as well. The dampness of the early morning or evening dew allows it to grow, and during the day, the hot and dry conditions will enable it to spread. When it comes to agents that spread their spores, wind and pests such as wolly aphids are the most common agents.
Apart from climatic and weather conditions, plant spacing also supports powdery mildew to grow. Overcrowded crops reduce air circulation, increase shade and cause dampness around the leaves.
Symptoms: How To Identify Powdery Mildew?
The most obvious signs would be the powdery substance on the leaves or, if the infection has gotten worse, on the stems or even fruits on your plants. They appear round and slightly raised from the leaf surface. In severe cases, the infected plant looks as though it has been seriously dusted with flour. The affected leaves tend to turn yellow or dry out and die if the fungi are left unchecked.
The loss of leaves can result in the scalding of fruits. That problem mainly affects cucurbits such as pumpkin, squash, melons, and cucumbers particularly, and when infected plants produce fruits susceptible to sunscald, the fruits end up having a poor flavor and don’t store well.
Different plants have different symptoms when infected with powdery mildew. For example, infections on the sedum can manifest as brown scabby spots. On tomato plants, powdery mildew often begins with pale yellow spots on the leaves that develop into the typical white powdery growth.
Can Powdery Mildew Spread To Other Plants?
As mentioned earlier, the mildew is host-specific. The chances of the fungi spreading are pretty slim, so not all the plants in your garden are susceptible to the infection. They only attack specific plants, and if you haven’t combined different plants, you might end up with an entire garden looking infected and unhealthy.
Types Of Plants Affected
It is quite unfortunate that very many plants are prone to infection from fungi. Powdery mildew can affect any plant from common vegetables to flowers to ornamental plants; the most vulnerable being plants such as zucchini, pumpkin, butternuts, cucumber, melon, eggplants, tomatoes, pepper, beans, kale, peas, mustard greens, lettuce, the green leafy part of carrots, cannabis, zinnia, apple trees, calendula, roses, sunflowers, begonia, bee balm, peonies, phlox and hydrangeas. For cabbages, collards, cauliflower and broccoli, the infection isn’t as bad as the rest of the aforementioned plants.
Types Of Plants Resistant To Mildew
Some plants do not readily develop powdery mildew. Despite having plenty of fungi in the garden, citrus, avocados, herbs such as sage, basil, figs, thyme, oregano and dill. Other plants include passion fruits, arugula, bok choy, swiss chard, onions, radishes, garlic, fava beans, ginger, strawberries and guava, among others, are highly resistant to mildew.
Can You Eat Vegetables That Have Powdery Mildew Fungi: How Dangerous Is It For Human Consumption?
While the fungi is a nuisance, it is practically harmless. It normally seems to have no severe effects on the human body, meaning it’s not toxic or poisonous. However, if you’re allergic to mold or mildew, it’s essential that you proceed with caution. Thoroughly wash the leaves before consumption and leave out the severely infected ones.
How To Prevent Powdery Mildew?
In the never-ending battle of mildew elimination, prevention is one of the most effective ways to control it. If only it were as easy as this article makes it sounds. However, I’m an avid believer that fungi can be kept under control, leaving most of your plants in great shape.
- Powdery Mildew Resistant Plants.
If you live in an area that supports the growth and spread of powdery mildew, it’s best to plant plants resistant to the fungi. You should also consider how often the fungi recurs in your garden. Refer to the mentioned plants earlier if you need a list of resistant crops.
- Good Plant Spacing
Ensure there’s enough space between the plants. The fungi thrive in humid and crowded environs where the air is stuffed. Follow recommended guidelines on plant spacing and allow proper circulation of air between the plants. If need be, prune to allow for more spacing.
- Clean Garden Tools
It’s always a great idea to sanitize your tools after dealing with infected plants. Mildew can be easily spread if handled carelessly. You may choose to use rubbing alcohol, white vinegar, hydrogen peroxide, diluted bleach or any other sanitizing agent to clean your tools before moving on to the next batch of plants.
- Don’t Use Infected Plants For Compost or Chop and Drop
The fungi have spores that survive and thrive in compost, spreading to other plants later on. Ensure that you get rid of the infected plants entirely by burning them or throwing them away in the municipal green waste bin.
- Aim For The Soil
If you’re watering your plants, try to aim for the soil instead of the leaves as much as possible. For plants that are already infected, water encourages the growth and spread of these fungi. You may opt to use drip irrigation for a perfect aim.
- Promote Overall Healthy Plants
Using various organic fertilizers such as compost tea and aloe vera extract boost the nutrients in the already healthy plants to maintain a robust immunity. By increasing the resilience to pests and diseases, the spread of powdery mildew will be kept under control. Additionally, to avoid drought stress, develop a watering schedule.
Neem oil can be used as a preventive measure and treatment for powdery mildew. For plants that tend to always get powdery mildew regardless of whichever preventative measure you choose to use, spraying neem oil every now and then can be a great way to reduce the rate of infection and spread on the plants. Crops such as zucchini and squash inevitably get infected. Nonetheless, it’s important to spray just enough to keep the fungi at bay. You don’t want to end up tasting neem oil in your food.
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- Polyculture and Inter-Cropping
If you’ve been gardening, you probably know by now that mixing up different plants wisely is a great way to maximize yields from your garden. By inter-cropping plants that are resistant to powdery mildew with those that aren’t, you can control the spread of the fungi and stop the infection from affecting other healthy plants. That, of course, sorely depends on how well you select your companion plants.
Other Cultural Preventive Measures Include
The sun is the enemy of fungal diseases. The longer you expose your plants to sunlight, the harder it will be for the mildew to grow and spread.
Newly formed tissue, lush, is very susceptible to powdery mildew. Adding Nitrogen will worsen the mildew problem in your garden, especially in the late summer.
How To Control Powdery Mildew? 8 Organic Methods
By the time you choose these remedies, the fungi have spread widely, and the infection is beyond prevention. They are homemade remedies that can be easily made.
- Baking Soda
Every household probably has a can of baking soda somewhere in their pantry and if you don’t have it, worry not. You can purchase it from a local store in your area. Baking soda is has a pH of 9; hence very alkaline. Because of this property, it is able to create a very alkaline environment killing the fungus. In severe cases, before purchasing a fungicide, this could just do the trick and clear most of the infection.
Mix one tablespoon of baking soda with a half teaspoonful of liquid hand soap to use it efficiently. Combine the two with a gallon of water. Proceed to spray the solution on the affected leaves, especially during the evening. Exposing the solution to sunlight may cause the leaves to experience sunburn.
Garlic poses sulfuric properties, which may also act as a fungicide. It works best when mixed with organic oil mixtures. You can also purchase garlic oil if you prefer not to make the solution at home.
For effective results, crush two bulbs (not cloves) and add to an organic such as the neem oil. Add rubbing alcohol and let it sit for two days. Strain the mixture and retain the crushed garlic. Soak the crushed garlic in a cup of water for a day, then dispose of the garlic. To a gallon of water, add the oil mixture and garlic water. When spraying the mix, make sure to spray only on the leaves and affected parts.
Sulphur is a natural product that can be bought in powder or liquid form and added to sulphur vaporizers. Follow instructions and ensure that you cover your hands with protective wear, shield your eyes and wear a face mask when handling it.
- Copper Fungicides
You can get this from the local store. Follow instructions closely and avoid using too much of it as it may cause damage to plants and soil.
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The oil is extracted from the fruits and seeds of the neem tree. It has the power to kill powdery mildew in less than 24 hours. The oil works by disrupting the plant’s metabolism and stop spore production. It also kills bugs carrying the spores and can also be used as a preventive measure, as mentioned earlier.
Mix three tablespoonfuls of neem oil with a gallon of water and spray on the affected plants for the next week, depending on how fast the mildew responds to the treatment.
Milk is currently being studied as to how or why it works so well compared to other inorganic fungicides. Many gardeners agree that natural compounds existing in milk fight the infection on the plant and boost the plant’s immune system, which also works to get rid of the fungi. Another belief is that it produces radicals that are toxic to the powdery mildew when exposed to the sun.
For the best results, mix 3 parts of water with 2 parts of milk or whey and spray on the affected plants during the day twice a week. For a much stronger effect, you may opt to spray undiluted milk on the affected plants.
- Potassium Bicarbonate
This fungicide works just like baking soda. It raises the pH to alkaline levels making the environment not suitable for the powdery mildew to survive. For best results, mix three tablespoons of bicarbonate with vegetable oil and a half teaspoonful of soap into a gallon of water. Once you’ve got the mixture right, spray on the affected plants.
While ordinary vinegar would also do the trick, it is advisable to use apple cider vinegar to avoid any harsh reaction from the plant. Be careful to properly dilute the vinegar because the high acidic content may burn the plant leaves. I would recommend four tablespoonfuls of vinegar mixed into a gallon of water. Spray this solution every three days.
Powdery mildew can cause some serious havoc if not carefully monitored. As you use the remedies above, make sure to do your due diligence and follow instructions on when to use the remedies. A few precautions are to note. Some ingredients such as vinegar and baking soda may cause sunburn to your plants. Ensure your plants are well watered before applying the remedies. It would be best to spray the treatment after daylight hours for better results and to avoid damaging plant leaves.