Powdery Mildew on Plants: How to Identify & Treat It

March 28, 2023

If you're seeing white, powdery spots on your plant leaves, you may be dealing with powdery mildew. It's a common fungal disease that can affect cucumbers, squash, melons, tomatoes, herbs and many other crops, including plants growing in a Tower Garden.

The earlier you spot it, the easier it is to manage. Here's how to identify powdery mildew, reduce the conditions that encourage it and treat affected plants before it spreads.

Is It Powdery Mildew?

Powdery mildew commonly appears as:

White or gray powdery spots on leaves.
Spots that gradually spread across more of the leaf surface.
Powdery growth on both leaves and stems.
Leaves that eventually yellow, curl or decline when infections become severe.

One important exception: Some plants naturally have pale or silvery markings on their leaves, so don't treat a plant simply because you see white coloring. Look for the characteristic powdery coating and whether it is spreading.

What Is Powdery Mildew?

Powdery mildew is the name given to a group of fungal diseases that produce a white or gray powder-like growth on plant surfaces. It often begins as small patches before spreading across larger portions of the leaves.

Unlike many plant diseases that thrive when leaves stay wet, powdery mildew can develop without standing water on the leaves. Crowded plants, limited airflow and favorable temperature and humidity conditions can all contribute to outbreaks.

Powdery mildew creating white patches on cucumber leaves

Why Is Powdery Mildew a Problem?

A small amount of powdery mildew may initially look like a cosmetic problem, but a significant infection can interfere with the plant's ability to photosynthesize effectively.

As the disease progresses, affected leaves may yellow, decline or drop prematurely. This can reduce plant vigor and, in severe cases, affect production.

Treating the problem early also helps reduce the chance of it spreading throughout densely planted crops.

Which Plants Get Powdery Mildew?

Powdery mildew can affect many plants, but Tower Garden growers often notice it on crops such as:

Squash

Cucumbers

Melons

Pumpkins

Tomatoes

Peppers

Strawberries

Dill

Parsley

Some varieties have better resistance to powdery mildew than others. Choosing disease-resistant varieties can be particularly helpful if powdery mildew is a recurring problem in your growing conditions.

You can browse our Tower Garden-ready seedlings when planning what to grow next.

How to Help Prevent Powdery Mildew

You can't guarantee that powdery mildew will never appear, but good growing practices can make conditions less favorable and help slow its spread.

Improve Airflow

Avoid letting plants become excessively crowded. Prune when appropriate so air can move through and around the foliage.

Use Air Circulation Indoors

When growing indoors, a fan can help keep air moving around densely growing plants.

Choose Resistant Varieties

When available, varieties with powdery mildew resistance can reduce your risk, although resistant plants can still become infected.

How to Get Rid of Powdery Mildew on Plants

If you've confirmed that powdery mildew is developing, start managing it as soon as possible. A small outbreak is generally easier to control than one that has spread throughout the Tower.

1. Remove Heavily Infected Leaves

Remove leaves that are heavily affected and dispose of them rather than leaving infected plant material around the Tower.

Avoid removing so much foliage at once that you severely stress the plant. Clean pruning tools after working with affected plants.

2. Improve Air Circulation

Prune overcrowded growth where appropriate and give plants more room for air to circulate. If you're growing indoors, use a fan to keep air moving around the foliage.

3. Use a Fungicide Labeled for Powdery Mildew

If the infection requires treatment, choose a fungicide labeled for powdery mildew and for the plants you're treating. Follow the product label carefully, including application rates, timing and any harvest restrictions.

We carry Garden Friendly Fungicide as one treatment option for growers dealing with fungal disease.

4. What About Using Milk for Powdery Mildew?

You may also see diluted milk recommended as a home treatment for powdery mildew. Research has found that milk sprays can suppress powdery mildew in some crops and conditions, but results can vary.

If you choose to experiment with a milk spray, test it on a small portion of the plant first rather than assuming that stronger concentrations will provide better control.

For a significant or persistent infection, a product specifically labeled for powdery mildew provides clearer instructions for application and use.

Important: Don't combine multiple sprays or treatments unless their labels specifically say they can be used together. Some products can damage foliage when combined or applied under unsuitable conditions.

Keep Checking Your Plants After Treatment

Continue inspecting your plants after treatment. Remove newly affected leaves when practical, maintain good airflow and watch nearby plants for signs that the mildew is spreading.

If powdery mildew repeatedly becomes a problem, consider whether plant crowding, variety selection or growing conditions can be adjusted for your next crop.