Cucumber Leaves Turning Yellow

Last Updated on June 15, 2023 by Grow with Bovees

We can safely confirm that when leaves turn yellow it is the plant’s way of communicating that there is a problem.

While green leaves are a clear indication of a healthy cucumber plant, cucumber leaves turning yellow is not.

Leaf discoloration will help you identify the problem with your cucumber plant and this article will guide you through all the possible reasons why your cucumber leaves get yellow spots or turn yellow.

Why Are My Cucumber Leaves Turning Yellow?

Cucumber leaves turning yellow can indicate diseased plants, and some possible causes include a high pH level in the soil, drainage issues, poor air circulation, damaged or compacted roots, pests (potato leaf hoppers), disease (cucumber mosaic virus), or a nutrient deficiency

The essential green pigment we need in the leaves of all healthy cucumber plants is called Chlorophyll and its job is to absorb sunlight, whereas abnormal yellowing of the leaves is called chlorosis.

How Important Is Chlorosis When Cucumber Leaves Turn Yellow?

Yellow spots on a cucumber plant indicate chlorosis, and although yellowing of the leaves of plants has many causes, correct identification allows for proper treatment and successful crops.

Chlorosis may be the underlying reason why leaves are turning yellow and dying, but can easily be fixed by adding a 2-inch layer of compost which will increase the nitrogen content.

Lack of Chlorophyll Causes Yellow Leaves

Cucumbers grow best in full sun and don’t survive in cool temperatures. When cucumber leaves indicate the loss of green coloration and turn yellow it’s due to insufficient chlorophyll.

Since cucumbers are a quick-growing crop, they thrive best in relatively high ground temperature and during the fruiting stage, it’s critical to apply a high-quality soil fertilizer that reduces cucumber leaves turning yellow.

Can Overwatering Cause the Yellowing Cucumber Leaves?

The yellowing leaves of your homegrown cucumbers can also be due to improper watering.

Remember, including rainfall, your plants require only about 1 – 2 inches of water per week.

When you have cucumber leaves turning yellow and the soil is saturated with water it may cause a plant to wilt due to oxygen-deprived roots.

How To Identify Nutritional Deficiency Cucumbers

The most typical nutrient problem related to chlorosis is the shortage of iron, although it may also be an indication for you to increase levels of zinc, potassium, or magnesium so let’s dive in and find out what other possible causes yellow cucumber plants.

Iron Deficiency and When To Spray Liquid Iron

Iron chlorosis is a yellowing of plant leaves without affecting the green veins of the plant.

Iron deficiency may be expected in calcareous soils and should be treated with chelated iron in powdered or granular form sprinkled around the soil.

While adding a 2-inch compost layer that contains sulfur makes the soil slightly more acidic and disease resistant.

Nitrogen is a crucial nutrient for healthy cucumber plant growth and nitrogen deficiency can be the underlying cause when growth is stunted and where the discoloration is most pronounced in the older leaves.

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When the upper surface of leaves is yellow along central veins and fruit production decreases, it’s likely due to nitrogen deficiency.

Although the plant may die within days, it’s easy to fix yellow cucumber leaves by simply adding one tablespoon of ammonium nitrate as a precaution when you see the first flowers start to bloom. 

Phosphorous and Zinc Deficiency

Phosphorus deficiency in severe cases completely prevents growth, and you should be on the lookout for small, stiff, dark green younger leaves.

Symptoms last only a few days and the affected leaves fade, the spots turn brown and the whole leaf shrivels before dying.

In zinc deficiency, the pattern is coarser than in iron and manganese deficiency due to the top leaves that grow close together, giving the plant a somewhat bushy appearance.  

Control by spraying with a zinc sulfate solution or if you live close to the ocean, try organic kelp for mulching.

Potassium Deficiency Symptoms in Cucumbers

Potassium deficiency spreads from the base towards the top of the plant, the oldest leaves being the worst affected and becoming bronzed and discolored yellowish-green at the margins.

Cucumber plant growth may be stunted while leaves remain small, but as chlorosis becomes more pronounced, it extends toward the center of the leaf, the main veins appear to have sunken and finally, the leaves will start to rot even though the cucumber vine remains green for some time. 

What Action Can I Take if My Cucumber Leaves Are Turning Yellow?

Because cucumbers are heavy feeders, start by applying a water-soluble, well-balanced fertilizer at the base of each plant or to the foliage, which can help the leaves present during application and overall healthy air circulation to the roots.

What Are the Common Pests That Attack Cucumber Plants?

Yellow leaves indicate pest infestation and plant diseases include a variety of insects and, unfortunately, may affect the growth of cucumber plants which are caused by bacterial or fungal infections transmitted by pests.

While insecticidal soap and neem oil are a good option, prevention is better than cure.

Tiny insects that infect cucumber plants can be eliminated by planting cucumber varieties using disease-resistant seeds, keeping the garden and surrounding area free of weeds that may potentially harbor insects that can spread cucumber mosaic virus and bacterial wilt.

Striped Beetles vs Spotted Beetles

Striped beetles can carry the bacteria that cause bacterial wilt, which is a serious disease and is transmitted once plants become infected by the bacteria that is carried from infected plants to healthy plants by the striped cucumber beetle and infected vines die within 7-14 days.

Spotted beetles most likely won’t survive winter and when the cucumber beetle larvae feed on the cucumber roots and underground sections of the plant, the feeding does not affect cucumber growth.

How Can I Protect My Garden From Beetles?

It’s rare to see spotted cucumber beetles and to discourage spreading plant disease to healthy plants, use row covers and plant in wide row spacing.

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Keep your garden clean, remove infested plants and infected cukes, debris, and other leaf litter regularly.

If a plant is showing signs of bacterial wilt, safely remove the diseased cucumber plants because they may be potential hosts for adults and spread the bacteria.

What Is Cucumber Mosaic Virus (CMV)

You’ll find that infected plants may suffer from stunted growth or the cucumber leaf edge is mottled, crinkled, and light green in color and several insects transmit these viruses.

It is no surprise that chemical control of the insects may minimize the mosaic virus but won’t be able to cure it in the long term.

How Do I Manage Aphids and Mosaic Virus?

Aphids reproduce rapidly, are small oval-shaped insects, and vary in size and color from light yellow to dark green or black.

They’re mainly seen on the underside of the leaves, where they suck the sap from the plants, and insecticidal soaps are generally only required if the infestation is aggressive.

Routinely, the cucumber plant is attacked by aphids after the vines form runners. The melon aphid is responsible for transmitting the cucumber mosaic virus. 

When the aphid population is low it can be pruned out to provide control; use tolerant seed varieties where possible and use reflective mulches such as silver-colored plastic which may deter aphids or by blasts of water on robust older plants to knock aphids off from the infected leaves.

When sucking out the plant sap, they excrete large amounts of a sugary, sticky substance known as honeydew which is a source of food for a black fungus known as sooty mold loved by ants.

How Can Beneficial Insects Help With Fighting Pests and Disease?

When the ants visit aphid colonies for the honeydew they will protect the plants from attack by other insects and may move them to other leaves.

Aphid infestation usually peaks during hot dry summers and when making treatment decisions consider natural control by introducing good companion plants which have reduced the efficiency of the natural enemies.

Remember, minute pirate bugs just as bees are essential for cucumber production and they should be looked after when you decide on which action should be taken because there are many other beneficial insects and aphid enemies that help fight disease or pests.

What Are Spider Mites?

Adult mites are very difficult to see, reddish-orange while some species have 2 to 4 dark spots on the back of their oval body shape. 

Don’t be fooled by their size, these little guys are destructive and affect cucumber plants in any growth stage.

How To Prevent and Control Spider Mites on Affected Plants

They spin fine webbing when the population is high and enjoy sucking chlorophyll from the undersides of leaves, creating fine white spots referred to as yellow stippling on the upper surfaces. See our post on how to get rid of spider mites here.

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Mite populations enjoy plant debris, hot, dry, and dusty areas so try to hose off plants to clean and dislodge the mites on the undersides of the leaves but be cautious, because spraying badly damaged leaves can cause further destruction.

Potato Leafhoppers in Cucumber Plants

The adult potato leafhopper is a bright-green, wedge-shaped insect while the potato leafhopper nymphs are smaller than adults, pale green to yellow.

Why Are My Cucumbers Dying?

The potato leaf hopper injects toxic compounds into the plant that may permanently reduce a plant’s ability to efficiently photosynthesize. 

Initial symptoms of leaf hopper feeding include paling of leaf veins and curling of leaves. However, feeding on plants can take place for several weeks before their damage becomes visible. 

Symptoms include the typical triangular yellowing or browning of leaf tips (called hopper burn). 

Here are two fungal diseases to watch out for.

Fusarium Wilt vs Verticillium Wilt

During fusarium wilt, the leaves of mature plants will initially become a dull green while the older leaves turn more yellow and continue to turn brown and dry up before the entire plant collapse.

Since Fusarium is a soil borne virus, the symptoms will tend to develop in hot spots in the soil which will slowly expand and reach other areas within your garden.

Verticillium wilt, which survives up to 8 years in soil, typically develops symptoms during fruit set when the leaves begin to wilt.

When roots of susceptible crops grow nearby, it may infect the roots and symptoms are often observed on one side of the plant and, as with Fusarium wilt, the xylem tissue (water-conducting tissue) will become tan to brown causing plugging and interference with water movement within the plant. 

Can You Overwater a Cucumber Plant?

Anthracnose leaf spot and Alternaria leaf blight occur on cucumber leaves that start as water-soaked areas on the cucumber leaf surface and expand into brown spots which are roughly circular due to irregular water-soak leaf spots.

Signs of Downy Mildew on Yellow Cucumber Leaves

Growers need to avoid overhead watering if they suspect downy mildew. When you see yellow spots on top and dark mold on the bottom of the leaf, Downy mildew lesions can appear angular, whereas powdery mildew has a noticeable white, moldy growth.

Did You Plant Cucumbers in the Right Conditions?

In severe cases, downy mildew can cause premature death of leaves, reduce yield and fruit quality and the first signs include pale yellow leaf spots. In time, it will cause the plant to weaken, and the cucumber fruit ripens prematurely with a club-shaped appearance. 

How To Take Care of Cucumber Plants

In conclusion, I believe that this article explained the disease signs in-depth, the difference between common deficiencies, and what to look out for in infected plants, and the suitable treatments.

By looking at leaves we can determine what the problems are, fix them and keep on doing what we enjoy, staying happy and healthy.