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

In this article, we will go through 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 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 leading causes of chlorosis in cucumber leaves fall into various categories. These include pests, diseases, light/water problems, and nutrition deficiencies.

Below, you can find out how to diagnose and fix each cause 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 

spider-mites-on-leafThese 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 fine silvery webbing.



You can quickly identify an aphid due to its oval-shaped appearance.

They can be 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 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 to feed.

It does so by releasing a toxin that induces yellowing in the leaves, causing them to fall from the plant ultimately.

Solution for Plant Pests

Pests can be a hassle, but it is usually relatively easy to deal with them once you find what type infests your plants.

The first step is to purchase insecticidal soap that you can spray around the leaves.

This will eliminate any pests and allow the cucumber leaves to heal naturally.

If you use the plants for food, use a strong water spray to remove the pests and make use of 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

cucumber-mosaic-virusIf, upon inspection, you find that your cucumber leaves are wrinkled with a downward curve, then there is a good chance the cucumber mosaic virus infects them.

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 transmission 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-leavesFusarium wilt is a fungus that causes older leaves to yellow from the edges and slowly spreads 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, which can infect your cucumber plants if they are grown in soil used previously for vegetables such as potatoes and peppers

Downy Mildew

downy-mildew-leaveIf 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 keep your plants in high humidity conditions, you may also notice a grey fuzz on the underside of the leaves.

Luckily, there are several ways to 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 plants’ air circulation and keep leaves dry with wide row spacing and a drip irrigation system.

Downy mildew can also be treated with a fungicide. They are most effective when used early in the disease, so 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 lead to yellow cucumber leaves. 

Potassium Deficiency

One of the most common deficiencies in cucumbers is potassium, which is because they generally have a high requirement.

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 a well-balanced fertilizer. You can also consider treating the soil for alkalinity 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 turn 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 ensure that you don’t overdo it with the fertilizer since this can stop the plant from producing 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 plant’s growth may be stunted, and leaves tend to be smaller.

If you have this problem, 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 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.

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

We hope this article helps you towards a bountiful and disease-free harvest this season.

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