White Spots On Squash Leaves – What To Do

It can be a worrying time to see your squash plant leaves turning white for no apparent reason. Luckily, when you see your squash leaves turning white, there are things you can do to get rid of them.

When plant foliage is dry, light is low, temperatures are moderate, and humidity is high, powdery mildew develops. Powdery mildew thrives in the late spring and early summer when the evenings are still cool and humid, but the days start to warm up.

In this guide, you can learn how to treat your zucchini plants and deal with this white powdery mildew. By the end, you’ll know how to control powdery mildew on your zucchini leaves and any other plants you spot it on around your garden. (Learn When to Harvest Butternut Squash)

White Spots On Squash Leaves

How Do You Treat Powdery Mildew on Squash Plants?

Powdery mildew isn’t always lethal to plants; it’s more of a cosmetic worry. Powdery mildew can leach nutrients from the plant if left untreated, eventually causing the leaves to wither and yellow.

This makes flowers look unattractive and exposes vegetables and fruit to the sun, where they can burn. Powdery mildew can impair a plant’s potential to produce and alter the flavor of fruit and vegetables.

Wind spreads powdery mildew spores, which can survive the winter in a waste pile, compost, or other plants. It is good to know that even if you have powdery mildew on squash, it doesn’t mean it’ll infect all your plants. (Learn How To Tell When Zucchini Is Bad)

If you spot your zucchini leaves turning white or your roses and other plants, it’s better to take precautionary actions, such as those stated below, to ensure that your other plants are not exposed to conditions that promote their growth.

Planting crops that are resistant to powdery mildew is one strategy to keep powdery mildew at bay. If that isn’t an option, there are a few additional things you can do:

  • Make sure you have sufficient spacing between plants to provide air circulation.
  • Don’t over-fertilize plants as fresh growth is susceptible to powdery mildew.
    Put plants where they will receive sufficient light and avoid shady spots.
  • Make sure soil can drain adequately. Poor drainage is ideal for disease-causing organisms.
  • Boost nutrient levels with compost in your soil, which leads to an increase in beneficial microorganisms.
  • Maintain plants by removing dead or diseased stems and foliage.
  • Use preventative treatment options such as garden fungicide or use preventative measures to prevent powdery mildew.
  • Squash that grows without enough sunlight and is crowded and temperatures are around 60 to 80 degrees Fahrenheit in the early summer are most prone to fungus infection.
  • Plant squash where they will get at least six hours of daily sunlight.
  • Thin out by removing existing plants to create the correct spacing, which should be around 2 feet apart for most squash types and up to 4 feet apart for larger strains. Correct spacing ensures good air circulation, which also helps prevent mildew fungus.
  • Water your squash plants around their base. Wet foliage can be prone to powdery mildew more than dry foliage. Splashing water also has the potential to spread fungal spores from infected plants to others.
  • Water squash plants once or twice weekly and moisten the top 6-inches of soil. Drought-stressed plants will suffer more from mildew infections than non-stressed plants.
  • Trim infected leaves with clean pruning shears as this slows the fungus’ spread.
  • Spray affected squash plants with a horticultural oil, or fungicidal oil, or even neem oil, at the first symptoms of powdery mildew growth. Reapply your oil treatment at 10-day intervals to get rid of powdery mildew. Don’t apply oil if temperatures reach over 90 degrees Fahrenheit or if your plants suffer from drought stress.

Causes White Spots on Squash Leaves

What Causes White Spots on Squash Leaves?

In terms of appearance, the disease is noticeable and first shows as reddish-brown patches on the surface of older leaves. (Read White Spots on Cucumber Leaves – What to Do)

It can be tough to see at the first onset, yet as it spreads, the white mildew covers leaves, petioles, and stems. Leaves look as if they have been sprinkled with powder. At this stage, leaves fade from a natural dark green color to pale yellow, brown and then die, exposing your squash to sunburn.

Conidia (spores) form quickly, and any wind or air movement transfers them to other nearby plants and leaves. From the time of infection to spotting the symptoms, it takes three to seven days.

Powdery mildew grows in densely planted areas that receive low light, and there is high relative humidity.

The infection starts in weather conditions and temperatures ranging from 50 to 90 degrees Fahrenheit, although it prefers warmer temperatures up to 80 degrees Fahrenheit. Night temperatures are also vital as they rise and offer ideal conditions for the spores to reproduce.

However, you won’t find diseases growing beyond 100 degrees Fahrenheit when the weather is hot. Powdery mildew can spread in cucurbits since this disease overwinters well and will be passed on to the next generation of squash.

Crop rotation can help reduce the spread of powdery mildew, and any cucurbits shouldn’t be planted in the same areas for the next season or the next year (two years).

Keep gardens clear of weeds as they can spread via these or use them to live through the winter. Powdery mildew control may need to use of a fungicide at the right time.

For using a fungicide spray, it’s too late when symptoms are widespread. Fungicides work by prevention your squash plants healthy foliage; therefore, you need to identify any white powdery infection as soon as you can.

You can choose organic horticultural oil fungal sprays, and you can control the spread with sulfur and fixed copper fungicides.

Powdery mildew can be controlled by spraying neem oil solution; However, it doesn’t matter what you use; it needs application early before the disease can spread throughout the foliage and infect another leaf.

How Do I Get Rid of Powdery Mildew In My Garden?

There’s no need to panic if your plants show signs of powdery mildew. Many solutions can be found using items you may already have in your home. Here are some treatments that were found years ago and proven to be effective in curing the disease:

Baking Soda effective as a powdery mildew treatment

Baking Soda

Baking Soda is an ingredient used in the kitchen. While it isn’t highly effective as a powdery mildew treatment by itself, it is effective to control powdery mildew when you mix it with liquid soap and water. (Read Powdery Mildew Cucumber Issues)

When used as a preventative strategy and not a treatment, it is usually the most beneficial. Mix one gallon of water to one tablespoon baking soda and one-half teaspoon of liquid dishwashing soap. Spray the solution around the leaves of your plants.


You rinse your mouth with mouthwash to kill bacteria, so; it was seen years ago in gardening circles; you can use mouthwash to kill powdery mildew spores when used daily. Powdery mildew spores cannot tolerate mouthwash as it’s designed to kill bacteria.

Take 3 parts water to 1 part mouthwash. Although effective, you need to be careful of this as some mouthwashes are strong, and you can kill young plant growth.


Milk is gathering lots of attention as a promising gardening solution in the control of powdery mildew. It isn’t understood why it works, yet milk can work as an antiseptic and fungicide.

On your zucchini and other squash varieties, it works to avoid powdery mildew. Take One-part milk to two or three parts water as a good ratio that could be sprayed on healthy leaves in the morning to prevent mold on squash leaves.

White Spots On Squash Leaves - What To Do

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