Why Are There Yellow Spots on Cucumber Leaves?

why are there yellow spots on cucumber leaves

Yellow spots on cucumber leaves can be a sign of plant disease but it can also indicate less than ideal growing conditions. Find out the cause of yellowing leaves and treat accordingly.

Cucumber plants should be a bright medium to dark green throughout their growing season. The only thing you want to have with a different color is the flowers.

If you notice yellow spots on your cucumber leaves it is time to check into the plant health. It could just be a case of adjusting its growing conditions but it can also be a more worrying sign of plant disease.

This guide shows you the different possible causes of yellow spots on cucumber leaves and the appropriate action for each.

What Are the Yellow Spots on Cucumber Leaves?

The two main explanations for yellow spots on cucumber leaves is bad growing conditions or a plant disease. This is how you can identify the true cause.

Leaf Yellowing Due to Growing Conditions

These are the growth factors that might be the reason behind yellow cucumber leaves.

  1. Overwatering

Cucumbers need at least 1 inch of rainwater over a period of 1 week. Cucumber plants kept indoors also need a lot of water for healthy growth. However, too much water can cause leaf yellowing, a common signal of overwatering in most plants.

  1. Lack of Nitrogen & Potassium

Cucumbers need relatively high levels of nitrogen and potassium to maintain their green color. If the soil they are growing in lacks these nutrients, the leaves may start to fade and turn yellow.

  1. Not Enough Sunlight

The green compound chlorophyll is what allows plants to capture the sun’s energy. When cucumber plants don’t receive enough sunlight, the chlorophyll loses its color and the plant can become yellow.

cucumber too much sun

Leaf Yellow Due to Plant Disease

Unfortunately, yellow spots on the leaves can be an indication of many different cucumber plant diseases. Take a look at the symptoms of some of the most common ones.

  1. Anthracnose

Antracnose is a fungal plant disease. It starts out as small yellow circles on plant leaves that grow in size over time. Another key characteristic is black spots with pink centers on the cucumber fruit.

  1. Downy Mildew

Another fungal plant disease that prefers a dark and humid environment. The top of the leaf may have light green or yellow spots while the bottom of the leaf shows gray or purple spores.

  1. Verticillium Wilt

This is a plant disease that works its way up, starting from the stem of the cucumber plant. You can see a pattern of yellow spots running from the bottom and moving up. These spots will eventually turn brown.

  1. Alternaria Leaf Blight

The most common cucumber plant disease. This shows up as irregularly shaped brown spots on the leaves but they may have a yellow ring.

  1. Bacterial Leaf Spots

While alternaria leaf blight is fungal, this plant disease is caused by bacteria but still looks very similar. Bacterial leaf spots most likely start on lesions and quickly spread to other parts of the plant.

How Do You Treat Yellow Spots on Cucumber Leaves?

Once you have identified the problem, you can start to treat your cucumber plants. This is what you can do to try to save them.

Improving Growing Conditions

Most of these causes are a simple fix.

  1. Overwatering – Stop Watering

If you are growing the cucumbers indoors, simply stop watering them. Let the top 1-2 inches of soil dry out before watering.

When growing them outside, place a cover of the cucumber plants to protect the soil from rainfall. You should also cut off the yellow leaves to give it a better chance to recover.

  1. Lack of Nitrogen & Potassium – Add Fertilizer

Cucumbers only survive through one growing season and a short one at that but they might still need a booster. Add a fertilizer specifically for cucumbers to the soil, around the time that the cucumber plants start flowering.

  1. Not Enough Sunlight – Move or Trap More Sun

When growing indoors, just move the container to a brighter spot in the house. When grown outdoors, it can help to install a polytunnel.

cucumbers turning yellow

Treating Cucumber Plant Diseas

Cucumber diseases with yellowing of leaves is more difficult to solve. The treatment may also affect whether it is safe to eat the cucumbers.

  1. Anthracnose – Fungicide & Plant removal

Unfortunately, there aren’t any natural ways to treat anthracnose on plants. You can treat with fungicides but the cucumbers may longer be safe to eat. If only a single plant is infected you can remove it in the hopes that it hasn’t spread to the others.

  1. Downy Mildew – Baking Soda & Soap

There are many DIY solutions to treating downy mildew but perhaps the most effective is a mixture of 1 tsp baking soda, 1 tsp soap and 1 gallon of water. Combine these ingredients and liberally spray on the affected plants.

  1. Vertilicum Wilt – No Treatment

Unfortunately, there is no known treatment for vertilicum wilt. It is best to remove the plants so it doesn’t spread.

  1. Alternaria Leaf Blight – Leaf Removal

Leaf blight is very hard to treat so it is best to cut off the affected leaves as soon as possible. The baking soda and soap mixture for downy mildew may help it from spreading to other plants.

  1. Bacterial Leaf Spots – Baking Soda & Soap

Like with leaf blight, there is no known natural treatment for bacterial leaf spots. Here you can also try the baking soda and soap trick but remember to also remove the affected leaves.

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Frequently Asked Questions

Should I Cut Off Yellow Cucumber Leaves?

Cucumber leaves that have turned yellow or have yellow spots are best removed. Then, also identify why they may have turned yellow and treat accordingly.

Why Are My Cucumber Leaves Going Yellow?

Yellowing leaves can be caused by overwatering, not enough sunlight or lack of nutrients in the soil. It can also be the beginning stages of a plant disease.

How Do You Fix Yellow Cucumber Leaves?

If the yellow cucumber leaves are caused by poor growing conditions, it can easily be solved. However, if the cause is a plant disease it is more difficult to treat and might mean the entire plant has to be removed.


There are many possible reasons for why a cucumber plant might have yellow leaves. None of the reasons are good.

If it is due to a lack of sunlight, too much water or insufficient nitrogen and potassium they plant can be treated. When it is caused by a cucumber plant disease there might not be a safe treatment that ensures the cucumbers are still edible.

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