Is Cornstarch The Secret To Curbing Powdery Plant Mildew?

Is Cornstarch The Secret To Curbing Powdery Plant Mildew?

If you notice powdery mildew in your plants, you’ll want to act fast to prevent its spread. This fungal disease varies depending on the plant it affects. It’s not the same fungi in every outbreak, so if it affects one plant, it may not affect the others nearby. The best way to combat this disease is by preventing the conditions from becoming too moist around your plants. Removing infected plants is also a guaranteed way to prevent the fungi from spreading. Some people believe that cornstarch can prevent and cure powdery mildew, but there is no scientific evidence to support this claim. Since cornstarch is not an antifungal, there is no reason to believe it can stop fungal diseases.

Even though you can’t pull cornstarch out of your pantry for a quick fix, there are still many other easy ways you can take control of powdery mildew in your garden. Careful handling of your plants is the best place to start. Fungicides and horticultural oil can help, or you can use some common kitchen items.

Why cornstarch isn’t the best solution

powdered and liquid cornstarch


Powdery mildew can’t be cured, so it’s important to stop it before it’s too late. The spread can be stopped by removing the plant from the garden or slowing the spread with antifungal products like fungicides or baking soda. Baking soda is an antifungal agent, according to a 2013 study in the Mycopathologia Journal. Spray a solution with baking soda on leaves to hinder fungal growth. There’s word around the internet that cornstarch can behave similarly, but no factual sources support this belief. Cornstarch is made from corn endosperm. The fiber is removed from the kernels, and the endosperm is reduced to powder. Though flavorless and odorless, cornstarch is essentially just powdered corn with the healthy stuff taken out.

A 1959 study in the Nature Journal noted that young corn wasn’t infected by the same fungal diseases older corn develops due to antifungal substances in the young corn. The substances were shown to inhibit the growth of two fungal diseases successfully. While this does show promising signs, remember that cornstarch is developed from older corn, which can develop fungal diseases, and this old study doesn’t have any modern research to back it up.

How to treat powdery mildew

treating powdery mildew


The most effective way to combat powdery mildew is to remove it from the garden. Once a plant is infected, remove the entire plant or infected portion, depending on how bad it is. For small outbreaks, baking soda can stop fungal growth by making the area too alkaline for fungi to grow. Milk is a surprising at-home solution that has varying levels of success. Create a milk and water solution containing 20-30% milk and spray it on your plants once or twice weekly to control the outbreak.

Prevent powdery mildew in the first place by controlling moisture levels in the environment. Don’t overwater, and be sure to leave plenty of airflow between plants. Prune plants as needed to achieve enough air between them. If you allow infected plants to stay in the garden, remove them at the end of the season so the diseased debris doesn’t drop; the spores will stay through winter and infect new plants the following year.

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Dr Heidi Parkes

By Dr Heidi Parkes

Senior Information Extension Officer QLD Dept of Agriculture & Fisheries.