3 Causes of White Zucchini Leaves (Plus 5 Easy Solutions!)
Growing zucchini is satisfying, for sure. But seeing these strange white leaves on zucchini plants? Absolutely not! Sadly, thousands of home gardeners have experienced this time and time again.
Genetics, mosaic virus, and powdery mildew can turn zucchini leaves white. Foliage infected with powdery mildew can be sprayed or pruned to prevent further fungal dispersion. Although incurable, mosaic virus can be prevented using virus-free seeds and strict aphid control.
If you’re wondering what exactly is behind these white marks on zucchini leaves, you’re not alone. Continue reading to find out the answer!
1. Powdery Mildew
White dots and patches on zucchini leaves are indicators of powdery mildew. These spots will look similar to dust and will smear upon contact. This fungal disease typically occurs after the plant is splashed by water droplets containing spores.
If you’ve ever looked at your zucchini and wondered who sprinkled powder all over your delicious crops, it’s probably powdery mildew.
Powdery mildew is a fungal disease that affects a large range of plants from trees, to houseplants, and even vegetables. This is different from spider mites, which are insects that leave white webbing on plants, although equally as irritating.
The symptoms are true to their name. Infected plants will display white patches or dots which are frequently seen on the lower and older leaves of the zucchini.
This disease is usually spread after droplets of infected water splash up onto the leaves or the plant itself. Due to this, it’s recommended to check your zucchini thoroughly after rain.
2. Mosaic Virus
Zucchini leaves infected with mosaic virus typically display crinkled and mottled foliage with yellow and white mosaic patterns. This virus can be seed-borne or spread through insect or mechanical transmission.
This virus is the equivalent of the common cold for the cucurbits family and happens to many squash and zucchini plants. So don’t feel too bad if you happen to spot this, it’s that common.
Want an easy way to identify it? Check for yellowish-white mosaic patterns on foliage and look for mottled leaves.
Affected plants will also produce discolored and bumpy zucchini that may even wilt. But other infected zucchinis can sometimes be asymptomatic. So keep an eye on your plants regardless.
Some of the ways that the mosaic virus can be spread are through infected aphids or the use of unclean tools or hands.
This is assuming the pathogen did not come from the seed itself, which is unfortunately common. This virus can even live in bodies of water, soil, and dead plant tissue for long periods, making it extremely challenging to combat.
Genetic mutations in zucchini plants can sometimes cause white, symmetrical patterns on zucchini leaves. White and silver markings on zucchini foliage are a common occurrence and only result from a minor superficial mutation.
Lastly, some potentially good news.
If the white markings on your zucchini leaves are near symmetrical, silvery in appearance, and follow the veins of the leaf, this is most likely just by natural design.
These white-veined patterns crossing in between the lines of the leaves cannot be wiped off like powdery mildew and are not a sign of disease.
White and silvery patterns following leaf veins can sometimes be seen on zucchini leaves. If the pattern is symmetrical and cannot be rubbed off, this is most likely due to a natural genetic mutation of the plant.
This is probably just a characteristic of whatever variety you’ve planted. No issues here, you simply have a zucchini plant with its own unique pattern!
But what if these white dots aren’t just a pretty genetic anomaly? Don’t worry, this is fine too as long as you address it as early as possible.
2 Simple Ways to Remove Powdery Mildew in Zucchini Leaves
The 2 most effective ways of removing powdery mildew from zucchini plants are:
- Prune the affected leaves
- Use sprays
Here are some of the methods you can use to treat zucchini plants that have powdery mildew.
1. Prune the Affected Leaves
Zucchini leaves covered in powdery mildew must be pruned until the base. Remove infected debris immediately to prevent the spread of spores.
You might hesitate at the thought of chopping off your lush zucchini bush but this is greatly beneficial to the plant’s health.
Examine your zucchini plants closely and snip off any leaves with powdery mildew at the base of the stem. Be certain your shears are sterilized before and after you prune.
Using clean tools will help limit the spread of powdery mildew in your garden and help encourage the zucchini to grow mildew-free foliage.
The infected foliage you cut off and debris you have left over should be thrown in a separate garbage bag or burned. Avoid putting it in compost as the spores will only infect your months of hard work.
2. Use Sprays
To combat powdery mildew, combine 2 tablespoons of baking soda, 3 drops of dish soap, and 3 tablespoons of vegetable oil in 1 gallon of water. Spray infected zucchini leaves with this solution 1–2 times a week. Allow the plant to dry out by spraying it early in the day.
Milk is a popular ingredient I’ve heard people use for powdery mildew.
But the problem with using milk is that this can lead to an unpleasant smell. This may even attract flies, so use your own judgment here.
For an easy spray to help combat powdery mildew, you need baking soda, soap, and vegetable oil.
Mix all of these ingredients into 1 gallon (3.79 L) of water. You only need a few drops of the dishwashing liquid to help act as an emulsifier, so go easy on that.
Pour this mixture into a plastic spray bottle and spritz the infected zucchini foliage with it early in the morning. Repeat this once or twice a week.
This solution will create an inhospitable, alkaline environment that will prevent fungal spores from colonizing on the surface of the zucchini leaves. Plus, it doesn’t smell!
3 Ways to Prevent the Mosaic Virus in Zucchini Leaves
Mosaic virus can be prevented in zucchini leaves using 3 ways:
- Use pathogen-free seeds
- Control aphids
- Select resistant varieties
It’s unfortunate but there are currently no ways to cure plants infected with the mosaic virus. It may even be best to remove the zucchini entirely to prevent it from infecting nearby plants.
To help ensure this doesn’t happen again, here are some methods you can use to prevent white leaves in zucchini.
1. Use Pathogen-Free Zucchini Seeds
Purchase zucchini seeds that are pathogen-free from a reputable source to prevent the spread of the white mosaic virus. Additionally, zucchini seeds can be treated in hot water up to 122°F, for 30 minutes.
The mosaic virus can spread in a variety of different ways. But at the core of it all, this is primarily a seed-borne infection.
So of course, always be certain the seeds you’re planting are confirmed to be free of viruses. To be completely safe, you can also treat the seeds with hot water measuring up to 122°F (50°C) for about 30 minutes.
Lastly, try to refrain from using cuttings of infected plants for propagation. It might be tempting to try to salvage it but when a plant is infected, almost all of the plant tissue can be found carrying particles of the virus.
2. Control Aphids on Zucchinis
Strict aphid control is key to preventing zucchini from becoming infected with the mosaic virus which makes zucchini leaves turn white. Eliminate aphids with baking soda solutions and regular water hosing. Neem oil can also be used.
Aphids are the usual suspects when it comes to mosaic virus vectors.
A straightforward method of control is to just hose the aphids off your plants. Easy! This is great if the zucchini is being grown in a container.
But for the best results, try using neem oil or the spray mixture from earlier to kill all the aphids. Then, thoroughly hose the plant afterward to wash all of them off completely.
>> Learn more in our article about how to use neem oil.
Since you’re effectively eliminating the aphids this way, this technique is much better than hosing alone.
3. Select Resistant Zucchini Varieties
Zucchini varieties with partial or complete resistance to mosaic virus can be planted to prevent white zucchini leaves. These varieties include Butta F1 and Emerald Delight.
Luckily, we live in a wonderful age of science. Take advantage of this and consider growing zucchini varieties that are tested and confirmed to be resistant to the mosaic virus.
There are quite literally dozens of varieties available, so you have options!
Some of the most common virus-resistant zucchini varieties gardeners can grow are:
- Butta F1
- Desert F1
- Emerald Delight
- Rotem F1
However, be sure to look into the soil before planting anew!
If there is any infected plant matter left, the mosaic virus can live up to 3 months to even 2 years in the soil. It might be a hassle but consider replacing the soil entirely or using a different plot.
Are zucchini leaves edible?
Zucchini leaves are edible. If the leaves are covered in white markings due to powdery mildew, however, it is not recommended to eat them. The consumption of mold can cause adverse effects and even serious illness for those with allergies.
Can you eat zucchini fruit from plants affected by the mosaic virus?
The mosaic virus cannot harm humans as it only targets plants. The zucchini will grow to be severely disfigured compared to fruit harvested from a healthy plant but are not harmful for human consumption.
Summary of Zucchini Leaves Turning White
Some of the most common factors that can cause zucchini leaves to turn white are genetics, powdery mildew, and the zucchini mosaic virus. Symmetrical white patterns on leaves are natural and no cause for alarm.
Leaves altered by powdery mildew, however, must be sprayed with baking soda or pruned at the base to prevent the spores from spreading further. Since there is no cure for the mosaic virus, pathogen-free seeds and zucchini varieties resistant to disease must be utilized to prevent the leaves from turning white.
- “Growing summer squash and zucchini in home gardens” by n/a in University of Minnesota
- “Powdery Mildew” by Chuck Burgess in University of Clemson
- “Cucurbits, Zucchini Yellow Mosaic Virus” by n/a in University of Massachusetts