Updated at: 11-05-2022 - By: Helen Skeates

The sight of mildew on your garden plants is wearing you down, right? When it comes to killing powdery mildew spores, what temperature do you need?

You’ve come to the right place if you’ve asked yourself these questions. In this post, you’ll get the information you need to get rid of your powdery mildew infestations.

What Are Powdery Mildews?

Many fungal species produce powdery mildew, a widespread disease of plants. These include Erysiphe species, Golovinomyces species, Leveillula species, Oidium species, and Podosphaera species. A fungal spore (conidia) travels through the air and infects adjacent plants.

You can find out what powdery mildew looks like in this helpful article if you’re unsure if your plants are infected.

It is not necessary for the environment to provide free moisture in order for powdery mildew spores to germinate. Once a plant is infected, it is easy for them to spread.

What Temperature Kills Powdery Mildew Spores? Helpful Guide - Krostrade

A spore can germinate and produce new spores in as little as 48 hours. Cold nights and warm days with low relative humidity are ideal for powdery mildew’s spore proliferation.

Symptoms and Signs

A white to gray powdery growth appears on the surface of leaves and occasionally other plant components when powdery mildew, as the name suggests, is the cause of a disease. Leaves may turn yellow, then brown and die. An infected tissue may be deformed and malformed.

Comments on the Disease

Many powdery mildew fungi are very specialized, and there are many varieties. Squash plants can be infected by a powdery mildew that also affects other plants in the cucurbit family, but this mildew will not affect roses, and vice versa. Zinnias, on the other hand, can be infected by powdery mildew that also affects many other plants in the composite family. Unlike other fungi, powdery mildew can only thrive in the presence of living plant tissue. If no chasmothecia (the fungus’ s spherical resting stages) grow on the mildewed plant portion, the mildew will die with it.

It is common for powdery mildew fungus to form short food-absorbing projections (haustoria) in the epidermal cells as they grow on leaves. They produce large numbers of tiny airborne conidia (conidia) that can infect neighboring plants. There is no need for external moisture for powdery mildew spores to germinate while the majority of other fungi require free water to germinate and infect in the form of dew, guttation, rain, or water from overhead irrigation When powdery mildew conidia are exposed to water, they die. However, splashing water can disseminate spores.

In the absence of host tissue, the fungus forms a sexual stage (chasmothecia) that is resistant to drying and other environmental conditions. The fungus thrives in latent buds or actively on plant tissues on many perennial plants, such as roses. Most of California is plagued by powdery mildew, a fungus that thrives in semiarid climates and is less prevalent in locations with more rain.

Temperatures between 68 and 86 degrees Fahrenheit are ideal for powdery mildews. Mildew spores and colonies die when leaf temperatures reach 90°F or higher. Powdery mildew fungus thrive in conditions of low light intensity or shade, as well as high relative humidity (more than 95 percent). The disease can thrive in a greenhouse environment.


The most effective method of controlling pests is to utilize resistant cultivars. The creation of resistant cultivars for flower and nursery crops has received little attention. Mildews are less likely to infect plants in a greenhouse with more air moving around them. Powdery mildew infections are less likely to form on plants treated with anti-transpirants.

Monitoring and Treatment Decisions

Existing infections are eradicated, and healthy tissues are safeguarded, with fungicidal treatment. It has been found that some products are capable of both protecting the plant and eliminating it, especially if the plant is thoroughly wetted. Some of these items may require the use of surfactants in order to achieve optimum wetting.

Some of these fungicides have become ineffective against the fungus. In order to prevent fungal strains from developing resistance to fungicides, use a variety of different fungicides.

What Temperature Removes Powdery Mildew Spores?

Powdery mildew spores can be killed by leaf temperatures above 900F (320C). While spring and fall temperatures of 680F to 860F (200C to 300C) are ideal for the formation of this plant disease, same temperatures can also be detrimental.

What Kills Powdery Mildew Spores?

Another factor in powdery mildew death is the decomposition of the affected plant component. Having a live host is essential for their growth and reproduction, as they are obligate parasites.

Most powdery mildew spores, excluding those that infect grasses, die when they come into contact with water. Spores cannot germinate when water is present on the leaves of the plant.

Using a syringe and water, saturate the diseased area of the plant to kill spores. The spores will be flushed from the plant’s surface as a result of this.

How to Get Rid of Powdery Mildew During Flowering – Direct Garden Supply

Treatments that use chemicals as fungicides and are recommended for use if the disease is widespread are listed below.

1. Sulfur

When sprayed directly to the affected area of the plant, this fungicide stops the spread of disease spores. When combined with lime, it’s even more potent.

Sulfur can be hazardous to animals, as well as beneficial insects and microbes in the soil, if utilized in large quantities.

2. Neem oil

Powdery mildew can be treated using this fungicide, which is derived from the neem tree. Because of this, beneficial insects and microbes aren’t as negatively impacted.

3. Triforine

Ornamental plants, such as roses, benefit more from the use of triforine as a fungicide.

4. Potassium bicarbonate

When potassium bicarbonate comes into direct touch with powdery mildew spores, it immediately destroys them. Beneficial insects are less likely to be harmed by this treatment than by sulfur treatment.

Fungicides like this can be acquired from gardening supply stores like Home Depot or Lowe’s. For the duration of the plant’s growing season, apply chemical treatments every one to two weeks internally.

Make sure to follow the instructions on the container label while applying the product correctly. ‘ It is important to note that the use of different fungicide treatments varies based on plant species, varieties, usage rates, application times, and waiting periods before harvesting.

How Do You Keep Powdery Mildews From Spreading?

According to the above, chemical treatments can be used to kill spores and prevent future spread of plant disease. Instead of hazardous pesticides, you can also adopt the following cultural approach in an effort to limit spread of the disease.

Avoid using nitrogen fertilizer

In plants, the formation of succulent tissues, which are more vulnerable to infection, is aided by nitrogen fertilizer use, especially in late summer applications.

Avoid overhead watering

Powdery mildew spores prefer the increased humidity that overhead irrigation provides.

Get rid of infected plant parts

Cut or take out any infected components (leaves, stems, buds, etc.). There are many ways to inhibit the spread of the spores.

The soil will be contaminated if sick plant components are used as compost.

Heat and ventilation

Powdery mildew thrives in a dark, moist environment due of the lack of light and air movement. Remove overgrown plant materials by pruning or weeding them away to make more space for sunshine and airflow.

How to Kill Powdery Mildew Spores in the Soil

Fungal disease powdery mildew affects numerous plants and trees. However, it might have a negative impact on the health of plants. The fungus can be controlled in a number of ways, including through appropriate cultural practices. Neem oil can also be used to treat powdery mildew.

White Powdery Mildew on Soil

There are multiple fungi that produce powdery mildew, which can harm a wide range of plants and vegetables. Erysiphe, Leveillula, and Golovinomyces are all fungi that produce powdery mildew, according to the University of Massachusetts Amherst, and each species attacks a specific variety of plant. The white or gray powdery growth that grows on the plants is an easy way to identify the disease.

This disease is spread from plant to plant by wind rather than soil, as is the case with several other diseases, according to Rutgers New Jersey Agricultural Experiment Station. They can also survive the winter on bits of dead plants or on plants affected with the disease, according to West Virginia University Extension Service. Make a point to remove and destroy any infected plant components as soon as possible to minimize the spread of spores.

High humidity and temperatures between 60 and 80 degrees Fahrenheit are ideal conditions for powdery mildew infections. Make sure the plants are well-spaced and have a lot of air flow to avoid infection. Sprinklers and overhead irrigation should be avoided at all costs. Plant powdery mildew-resistant varieties, and rotate your vegetable garden’s crops if you have the option to do so.

Powdery Mildew Treatment | Way to Grow

Soil Solarization to Kill Pathogens

Temperatures above 90 degrees Fahrenheit may kill some powdery mildew spores, according to the University of Massachusetts Amherst. Soil solarization, an alternative to chemical pesticides, raises the temperature of the soil, killing spores and other pathogens that live on dead plant material.

Temperature and sun exposure are ideal for soil solarization at this time of year. Remove any rubbish or pebbles from the soil and break up any large clumps of dirt. Irrigate the soil and smooth the top layer. Before the dirt has a chance to dry, cover it with clear plastic. Avoid air pockets between the plastic and soil and tighten the edges of the plastic, recommends the Integrated Pest Management Program at the University of California in Davis.

For a period of four to six weeks, keep the plastic in place. When the sun is out, the soil will be warmed by its own heat as well as the heat that is trapped by the plastic sheeting. At a depth of 18 inches, the earth can be heated to a temperature of 90 to 98 degrees Fahrenheit. The soil’s surface will be significantly hotter as a result. Immediately after you remove the plastic, you can begin planting.

Fungicide Options for Powdery Mildew

Plants affected with fungus can benefit from fungicide treatments. Powdery mildew can be treated with neem oil, sulfur, or potassium bicarbonate, all of which are organic fungicides. Sulfur and potassium bicarbonate don’t cause fungi to grow resistant, unlike some other chemical choices. Burnt leaves might result if sulfur is employed in temperatures over 85 degrees Fahrenheit. Wait at least two weeks after using a sulfur spray before adding neem oil.

According to the West Virginia University Extension Service, you can produce your own powdery mildew spray by mixing baking soda and water together in a spray bottle. Spray your plants with a mixture of 1 teaspoon of baking soda and 1 litre of water. This will change the pH and assist to prevent powdery mildew from growing.

It is possible to use fungicides, such as trifloxystrobin or azoxystrobin, to manage powdery mildew on a wide range of plants in your yard. Ensure that any fungicide you apply on your vegetable plants is approved for use on that type of plant if the fungus attacks them. Make careful you read and adhere to the product label’s warnings and application instructions.

Things You Will Need

  • Plastic made of clear material.
  • a fungicide, whether natural or synthetic
  • It’s made of baking soda


To keep your garden looking its best, you need to know more about what temperature kills powdery mildew spores and how to avoid the development of this illness.

Powdery mildew thrives in conditions of low relative humidity, such as those seen during the day, and high relative humidity, such as those found at night. Fungal spores are killed by temperatures above 900F (320C), whereas the spores themselves are killed by lower temperatures.

To control the spread of plant disease, employ either cultural approaches or chemical treatments, and then assess which strategy is most effective.

If the conditions are right, mildews can grow on a variety of organic materials than just plants, such as wood, ceiling tiles, paper, carpets, drywall, and even food. For more information, see our helpful guide on how to remove mildew from patio cushions.