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What To Do About Cucumber Leaves Turning Yellow?

When cucumber leaves start to turn yellow, it isn’t always easy to figure out the reason why. Yellowing leaves are usually a sign of a sickly plant that needs urgent attention.

In this article, we will go through the reasons why cucumber leaves turn yellow and what you can do about it.

The Process Behind Cucumber Leaves Turning Yellow

As you may be aware, chlorophyll is the substance that gives leaves their green appearance. Yellowing leaves occur due to a lack of chlorophyll which is caused by a process known as chlorosis.

But, this process can occur for a variety of reasons so let’s take a look at the possible causes. 


Main Causes

The main causes of cucumber leaves turning yellow tend to fall into a specific category. These include pests, diseases, light/water problems, and nutrition deficiencies.

Below, you can find out how to diagnose the cause and fix it effectively. 


Everyone knows how much of a nuisance plant pests can be, and it is common for pests to cause discoloration in leaves.

Most insects won’t harm a plant, but certain pests can suck out the leaves’ sap and leave them turning yellow as a result.

Some of the most common pests include;

Spider Mites 



These critters are known to start sucking on cucumber leaves whenever they find them. This results in yellow stippling (light dots).

You can usually find them on leaf undersides, and they can be identified with their silvery fine webbing.



You can easily identify an aphid due to their oval-shaped appearance.

They can be both green and yellow, and they tend to leave behind honeydew. This is a black substance that tends to be sticky. 



To detect the presence of whiteflies, you can simply shake the leaves.

If you see a cloud-like appearance of small insects with a white appearance, you will know that your cucumber leaves have whiteflies.

They are similar to aphids in that both leave behind honeydew which can be detected. 


Potato Leafhopper 



This next pest is bigger than the pests we’ve mentioned so far. It thrives on sucking the sap from the leaves in order to feed.

When this occurs, they tend to release a toxin that induces yellowing in a leaf. This leads to damage, and eventually, the leaves will start falling from the plant. 

Solution for Plant Pests

Pests can be a hassle, but it is usually relatively easy to deal with them once you find the issue. You should purchase insecticidal soap that you can use to spray the leaves.

This will get rid of any pests and allow the cucumber leaves to heal naturally.

If you are using the plants for food, you can use a strong spray of water to remove the pests and use row covers.


Another common cause of cucumber plants turning yellow is diseases. Some diseases are easier to treat than others, and in some cases removing the plant will be the only option.

Yellow spots on cucumber leaves and streaks are commonly caused by the following diseases, which we will discuss below.

Cucumber Mosaic Virus



If upon inspection, you find that your cucumber leaves are wrinkled with a downward curve, then there is a good chance they may be infected by the cucumber mosaic virus.

The sad thing is that there aren’t any effective ways to treat this. The only option is to eliminate the infected plants since the virus can spread quickly by transmitting through pests.

It is crucial to note that the cucumber mosaic virus can live in soil and affect new plants in the next growing season. 

Fusarium Wilt


Yellowing and Wilting of Leaves due to Fusarium Virus Source-

Fusarium wilt is a fungus that causes older leaves to yellow from the edges and then slowly spread inwards. The carriers are the cucumber beetle larvae that feed on the root of the plant.

Sadly, if you confirm the presence of the disease, then you must remove the plant to stop it from spreading further.

Another similar type of fungus is verticillium wilt, and this tends to occur if your cucumber plants are grown in soil that was used for vegetables such as potatoes and peppers. 

Downy Mildew



If you notice yellow spots on the upper surface of cucumber leaves, then this can point toward downy mildew being the cause.

These spots tend to turn brown as the disease progresses. They also tend to have a noticeable patchwork appearance.

If you are keeping your plants in high humidity conditions, then you may also notice a grey fuzz on the underside of the leaves.

Luckily, there are a number of ways that you can treat downy mildew and prevent it from occurring in the first place.

The best way to prevent it is by selecting cucumber varieties that already have resistance to the disease.

You should also maximize the air circulation of the plants and keep leaves dry with wide row spacing and a drip irrigation system.

If you do notice downy mildew, it can be treated with a fungicide. They are most effective when used early in the disease, which means taking swift action is vital. 

Nutritional Deficiencies 

You should be aware of the various nutrients that cucumbers need to grow and thrive. A lack of a single nutrient can lead to chlorosis. 

You can detect potential deficiencies by testing the soil in your vegetable garden.

Below are some of the most common deficiencies that can lead to yellow cucumber leaves. 

Potassium Deficiency 

One of the most common deficiencies in cucumbers relates to potassium, and this is because they generally have a high requirement.

In fact, they are a rare crop due to the fact that they have greater potassium requirements than nitrogen.

You will be able to notice potassium deficiency if you see yellowing at the tips and edges of the leaves.

Young leaves may have a dull appearance. Luckily, you can fix this by spraying some well-balanced fertilizer. You can also consider treating the soil for alkaline or acidity if needed. 

Nitrogen Deficiency 

Nitrogen is essential for all plants, and a deficiency can lead to yellowing alongside stunting growth. If the deficiency is allowed to progress, there is also the risk of the plant dying.

A key sign of nitrogen deficiency is when older leaves start turning yellow at the central veins and tips.

Fortunately, there is a simple solution to fix this.

Simply adding 2 inches of compost will increase the nitrogen levels. If that doesn’t fix things, you can try adding two tablespoons of fertilizer or one tablespoon of ammonium nitrate.

However, you should make sure that you don’t overdo it with the fertilizer since this can stop the plant from producing the cucumbers. 

Iron Deficiency 

If you notice that new leaves are appearing yellow with green veins, then this could point to iron deficiency, especially if the older leaves are still green.

It is fairly easy to remedy this by adding granular iron to the soil around the roots. Alternatively, you can use liquid iron on the plant.

Zinc Deficiency 

A key sign of zinc deficiency is older leaves turning yellow between the veins. The growth of the plant may be stunted, and leaves tend to be smaller.

If you have this problem, then you can spray your cucumber plant with zinc sulfate solution. 

Not Enough Sunlight

Sometimes the reason for yellowing and wilting leaves is simply that your cucumber plant is not getting enough sunlight.

This is possibly the most straightforward problem to fix since you can simply move the plant to a location where it can get at least 6 hours of sunlight a day.

Some cucumber varieties may require 8 hours of daylight.


Another common cause of cucumber leaves turning yellow is overwatering. Roots that are soaked in too much water can become deprived of oxygen which leads to yellowing and wilting of the leaves.

Cucumber plants generally require 1-2 inches of water per week. Soil drainage problems can be resolved with sand that can help to loosen it.

Alternatively, you can consider containers with large drainage holes.


You should now have a better idea of which steps to take if you notice your cucumber leaves turning yellow.

It is vital to take good care of your cucumber plants so that you can enjoy a splendid bounty of cucumbers when it is time to harvest.

Although there can be a variety of causes of yellowing, the solutions are usually easy to apply.

We hope that this article will help you out if you ever notice your cucumber plants turning yellow. 


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