What Causes Powdery Mildew? How to get rid of it?


I love vegetable gardening, and if you do too, you may have come across powdery mildew. There may have been times you might have seen that powder-like white substance on the surface of plant and tree leaves. Have you ever thought about what that might be, and what might be the reason for having such white spots on a living plant’s leaves? I was plagued by the stuff for years until I learned what it was and how to deal with it.

What Causes Powdery Mildew? Powdery mildew is a fungus caused by micro-organisms. It is problematic when there are damp humid conditions. This fungal disease can affect a wide range of plants leaving behind powdery substances that block the leaves from photosynthesizing.

Powdery Mildew is prevalent during the summer when its very warm and humid after recent rain. These fungal spores are spread by the wind and by the unsuspecting gardener brushing against affected plants. They will completely cover leaves with a white powdery substance hence the name. This blocks the leaves from turning the suns light source into energy for the plant to use.

So, what is this white substance? How is it formed? How does it affect the plants? In this article, I will explain everything you need to not only be able to identify powdery mildew, but to understand where it comes from and how to prevent and treat it.

Causes of Powdery Mildew

Powdery Mildew is a fungus caused by microorganisms. As we have already discussed it is caused by warm humid conditions that provide an ideal breeding ground for powdery mildew to spread and infect not only the rest of the plant but adjacent plants too.

This fungal disease can affect a wide range of plants and trees and can prove to be extremely detrimental to plant growth. Imagine putting a bucket over your favourite plant for a month. Would it still look good after this time? No. Because we all know plants need light to thrive. Powdery Mildew restricts the light the plant is able to utilize.

So, how is powdery mildew caused? We now know that it is caused by Fungus infection and that it is a very prominent plant disease. This disease on the plants is caused by many types and species of fungus such as Erysiphe, Phyllactinia, Microsphaera, Podosphaera, Uncinula, and Sphaerotheca.

There are a lot of species of shrubs, trees, vines, flowers, fruits, vegetables, field crops, weeds, etc that are affected by the powdery mildew disease.

So what makes the appearance white and powdery? It is basically due to the presence and formation of microscopic spores in very large numbers. These spores are wind-borne and they do not need a medium like water for germination to spread the infection further.

These microscopic spores are also known as conidia and are produced every 3 to 14 days. The ideal condition for the spread of this disease in your plants includes a low level of moisture in the soil along with high humidity levels on the surface of the plants or the environment in which the plants are growing.

Once the fungus takes over any one of your plants, the many spores of the mildew can spread to other plants through wind and can greatly impact the growth and health of your plants.

Symptoms and Identification

Powdery Mildew is very easy to identify providing you have seen it before. But, if you are new to gardening it may be that you have never come across it and do not know what is taking over the leaves on your plants. It is therefore very important that you know the symptoms and ways to identify the disease on the plants.

What are these symptoms and how can they be identified? The various symptoms and the way to identify can be found below:

  • White flour-like powder all over the leaves
  • Usually starting in the form of circular white spots that can appear throughout the plants including leaves, stem, fruit.
  • This infection can usually be found on the upper side of the leaves. but over time as the fungus spreads, it will cover the entire plant.
  • Young plants are more vulnerable to damage caused by this disease. The leaves turn pale yellow and completely dry out. This is because they are limited in leaf growth at this stage, so a larger percentage of the plant is covered
  • The plant usually has restricted growth due to the lack of photosynthesis.
  • The buds, growing tips of the leaves will appear disfigured.

All of the above symptoms will appear later in the growing season. The diseased plants that are just growing fresh new leaves on the plants. Older leaves can become infested and it is best to remove them. Plants such as cucumbers, squash, pumpkin and marrow will get powdery mildew as the season progresses.

This disease would have quite a serious impact on all plants. Let’s look at the effects of this disease on all plants in a little detail.

Effects of Powdery Mildew

Some of these symptoms are in fact a result of this disease. So the disease leads to the symptoms that we mentioned and are also the indicators of this infection. Let us quickly see the effects of powdery mildew on plants.

  • Leaves start to curl upwards and also twist in varying ways leading to the exposure of the lower side of the leave.
  • The budding of flowers and the growing fruits on the plants get affected as the buds are covered with the powdery white substance that can lead to fruits and flowers rotting.
  • If affected seriously, the leaves turn brown in color and drop sooner than expected and abruptly.
  • The disease can result in the deformity of leaves and can lead to retarded growth of all plants infected by powdery mildew.
  • The disease can result in the overall reduction of fruit and crop yield.

If left unchecked and untreated, one infected plant can lead to all of your plants contracting powdery mildew. Avoiding this situation is a must. It is therefore imperative to take preventive steps so that the disease does not occur in the first place.

However, there are treatments available to help control powdery mildew should you contract it on some of your plants at home. Let us see how we can go about making sure that the disease does not occur in the first place.

Prevention Methods for Powdery Mildew

It is a well-known fact that prevention is always better than cure. So, your first endeavour should be to try and ensure that your plants do not catch Powdery Mildew. By following the steps below you can rest knowing that you have taken every possible action to ensure your plants are not infected.

  • Garden husbandry is really important
  • Ensure correct plant spacings
  • Consider watering applications
  • Spray with fungicides as a preventative
  • Monitor your plants for the signs and symptoms
  • Deal with affected plants quickly

Garden husbandry

Garden husbandry is really important when combating any pest or disease in the garden. Hygiene is of paramount importance in stopping their spread. Removing decaying plant matter such as leaves from the soil surface will ensure that affected leaves are removed from growing areas

Ensure correct plant spacings

Airflow will help to prevent powdery mildew. By using proper planting spacings you increase airflow allowing plants to dry off completely after a rain. This also helps with lowering humidity and heat levels which are exactly what the disease requires to thrive

Consider watering applications

During summer months you can drastically reduce the chance of contracting this virus as it requires damp or wet leaves to take hold and thrive. By ensuring that water is kept at the root level and not overhead you can reduce the moisture on the plant’s canopy.

Spray with fungicides as a preventative

Fungicides can help as a preventative this will kill any powdery mildew spores should they try to inhabit your plants. Preventing them from getting a hold can really help you in combating this disease.

These are some of the steps you can possibly take to prevent fungus infection in your plants. Apart from these you can check the situation and take appropriate action that may deem fit at that time and you can take preventive steps on a case to case basis.

Monitor your plants for the signs and symptoms

The earlier you can catch any signs of Powdery Mildew the better and easier it is to stop it in its tracks. Checking over your plants during watering will allow you to spot the signs and symptoms of powdery mildew and allow you to take action.

Deal with affected plants quickly

When you find plants that are affected, it is important to deal with them quickly. If allowed to continue to spread it can affect the whole garden. By either removing plants that have a large infection or removing the leaves of plants that are showing the signs of infection, you can get it under control. Consider spraying with the treatments below

Steps to take before treatment

Before you start any kind of treatment of the fungus, you will have to take certain steps to ensure that the treatment is effective. These steps can be a preliminary preparation for the treatment or part of the treatment itself. The various steps that you can take for treatment are:

  • Make sure that you plant your plants in sunny locations that get ample sunlight.
  • Make sure you prune plants in a timely manner to ensure proper air circulation. After every cut don’t forget to disinfect your pruning tools.
  • If there is a small section of the plant with major infection, make sure that you remove the diseased part and clean up the debris from the ground.
  • Make use of some organic compost to mulch the ground after cleaning up the area so that the diseased spores do not rise up to the plants.
  • Use milk sprays and keep spraying your plants from time to time preferably every 10 to 14 days.
  • Wash your plants occasionally so that any daily formation of spores can be prevented.
  • Make sure that you are watering the plants during the early morning so that they get the whole day to dry. Use drip irrigation and techniques like soaker hoses to keep them dry.
  • Make sure that you are using some slow-release fertilizer of organic nature so that excess nitrogen is prevented.
  • Make sure that all the plant debris that is collected after the harvest season are destroyed. Composting could have been a good option but if there has been fungus infection it is better not to compost.

The above steps take care of the preparation of the treatment of the infection. Now let us look at the treatment of the disease.

Effective Treatments

There are many tried and tested methods of treatment of Powdery Mildew. To begin treatment you must understand that every fungal infection is different from others. Different fungi will infect different sections of the plants based on the species of the plant and also the fungi.

If you follow the preventive steps properly this disease may not occur to your plants. If however your plants get infected anyway, then you can opt for any one of the following treatment methods below.

  • Apply Fungicides
  • Baking Soda Solutions
  • Neem Oil Solutions
  • SB Plant Invigorator
  • Whole Milk

Apply Fungicides

This is one of the most effective treatments against this disease. You can use sulfur dust or copper-based organic fungicides to prevent any infection to vulnerable plants. For getting the best results to make sure that you apply the fungicides at the earliest instance and appearance of the signs of disease.

To prepare the sulfur solution take 2 parts of sulfur and 8 parts of water. Sulfur is a strong element so this proportion should work. You may change the proportion based on the nature and the intensity of the spread of the disease. Mix thoroughly to ensure that the sulfur has dissolved thoroughly.

Start by spraying all the plants in the affected area and repeat every 7 to 10 days. Do not apply this during the height of daytime temperatures. This may destroy the crops and plants and may do more harm than any good.

Baking Soda Solutions

Baking Soda is one extremely useful powder that acts like magic in a lot of applications in our daily lives and the use of baking soda as an antifungal substance has been tried and tested. You can use baking soda as an antifungal solution for the plants. Here’s how you can make the solution.

Mix some baking soda in water and make a solution. Mix this in a 70/30 water/baking soda. Use a hand sprayer or a gardening sprayer and make sure to spray the solution to all your affected plants.

Assess the results and then repeat the process every 5 to 10 days. In most cases, the results start appearing rather quickly but if it does not, you might need a stronger fungicide to kill the infection that has taken over your plants.

Neem Oil Solution

The neem tree is known for its magical antibacterial and antifungal properties along with a lot of applications in the world of medicine. Neem oil is another most preferred and highly effective natural and organic way of treating the powdery mildew disease. In fact, it is not only effective in curing the fungal infections, but it would also help your plants in getting rid of any other kind of infections, insects or bugs, etc.

To prepare the solution, pour some neem oil in water and mix the solution thoroughly. 40% neem oil in 60% of water shall do the trick. Pour the solution into a sprayer and start spraying through all your affected plants. Neem oil will bring very fast results. You can assess the results in a few days and keep repeating the application process every 5 to 10 days until the fungal infection is completely destroyed.

SB Plant Invigorator

SB Plant Invigorator is a soap-based solution that was designed by a commercial tomato grower who got fed up of blights and mildews taking his crops. He designed this product as a way to not only combat these sorts of pests and diseases but to also provide elements required for the plant’s recovery.

The above are some of the most effective treatments for treating Powdery mildew or fungal infections in plants. If you have noticed, all these treatments are organic and are commonly available.

Plants that are more prone to Powdery Mildew.

  • Marrow
  • Cucumber
  • Zucchini / Courgette
  • Squash
  • Pumpkin
  • Gourds
  • Peas
  • Cereal
  • Grasses
  • Apple
  • Blackcurrant
  • Gooseberry
  • Grapes
  • Rhododendrons
  • Azaleas
  • Roses
  • Oak Tree
  • Sage

Powdery mildew can be a problem for many people. This is not the only disease that you may come across. Other diseases and pest can plaque your growing, such as the ones below. If there is a link included this will take you to other blog posts I have written on that subject to help you with your gardens.

Conclusion

In conclusion to answer the question raised – The cause of Powdery Mildew is the formation of microbial fungus-infected spores on the plants and trees. These fungi are of various types and species and they affect plants and trees of all types and species.

The best part is that this disease is absolutely curable and in fact can be avoided if the prescribed prevention methods are followed well. Prevention is better than cure, but if you do get powdery mildew then pruning of infected foliage can limit its spread.

Clean up of debris from areas around infected plants. Treatments include various organic sprays and powders, the use of Sulfur dust, Neem Oil and Baking Soda and SB Plant Invigorator along with some commercially available products.

I hope you enjoyed this blog post about Powdery Mildew. I trust it answered your question fully. If this was of interest to you, why not consider checking out some of my other blog posts and subscribing to the blog so you don’t miss future content.

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Remember folks; You Reap What You Sow!

Tony O'Neill

I am Tony O'Neill, A full-time firefighter and long term gardener. I have spent most of my life gardening. From the age of 7 until the present day at 45. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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