Cucumber Leaves Turning Yellow or Brown?

There’s nothing better than a crisp snack and a cool beverage during summer. Perhaps you want fresh slices of cucumber to snack on or a refreshing lemonade drink to battle the heat of the sun. It’s always more satisfying if the vegetable came straight from your garden and onto your plate or glass.

Summary

The most common reasons cucumber plant leaves often turn yellow or brown are because of nutritional deficiencies or disease. Viral and fungal infections are common types of diseases that turn cucumber leaves yellow or brown. Overwatering is the most common problem that can turn cucumber leaves yellow or brown.

Here are our favorite products for each cause.

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Cucumbers (Cucumis sativus) are sun- and water-loving plants since these are native to sub-tropical regions. They are fairly easy to take care of and can grow quickly, giving you a bountiful harvest.

However, there are times when things go wrong. Your plant may be wilting. Cucumber leaves can turn yellow, white, or brown. Leaves can develop black or white spots. It all leads to ruining the chances of it setting fruit.

To help you have a bountiful harvest, we’ll enumerate some of the most common reasons behind these issues. We’ll also include their respective treatment and precautions.

Why are the cucumber leaves turning yellow/brown?

Abnormal yellowing is called chlorosis, which happens when they lack chlorophyll. It’s an essential green pigment for survival. This can be caused by a range of things. Some of the most common causes are damaged roots and poor drainage.

Nutrient deficiency or high soil pH are also common causes. Other symptoms that accompany yellowing and browning (scorched leaf) wilting may be caused by diseases or pests. Things to look out for include lesions or unusual spots.

Table of Contents

wilting and yellowing

Image source: Guan, W., Egel, D., & Ingwell, L.

Diseases, Pests, and Problems

cucumber plant

There are a lot of diseases and pests that can cause a loss of yield in cucumbers. Suppose you noticed it wilting and developing spots or different leaf colors.

You’ve even given them enough amount of sun and other important things they need. In that case, you might need to check for diseases and pests.

It’s important to quickly determine the cause behind the symptoms your plants are experiencing. A pathogen or pest infestation may quickly spread and destroy your crop.

vegetable insect killer

Image source: Garden

Overwatering

The most common sign of overwatering is leaf yellowing or appearing limp. Roots become damaged and unable to absorb nutrients when the soil around them is too moist or submerged in water.

Overwatering can cause root rot because moist areas promote the growth of molds. Since overwatering leads to the inability of roots to absorb nutrients, they will also suffer from nutrient deficiency. It eventually leads to chlorosis.

To solve this, all you need to do is reduce watering to only when it truly needs it and make sure to get rid of any standing water around the base. Ensure that your garden bed or pot has good drainage.

overwatered cucumber plant

Image source: Stack Exchange

Nutrient deficiency

The appearance of chlorosis (yellowing) will be different in terms of where it manifests in the leaves, depending on the type of nutrient deficiency.

boy eating cucumber

This is the most common reason for chlorosis in most plants since nitrogen is involved in producing an important pigment, chlorophyll.

  • SYMPTOMS – Chlorosis develops in older leaves first, then progresses towards younger ones.
  • REASON – Nitrogen is required in chlorophyll production, the green pigment that traps the energy from sunlight. As a consequence, a shortage of nitrogen reduces the capacity to get energy during photosynthesis.
  • A nitrogen-deficient vegetative growth (stunted growth) and fruit production are both severely restricted. If it is nitrogen-deficient during the flowering stage, the fruiting potential will be affected negatively. Yield will be low with distorted and discolored fruit, or fruits may not develop at all.

J R Peters

Here’s a great all-purpose fertilizer we recommend.

NameJ R Peters
Formula20-20-20 All-Purpose Fertilizer
Item FormPowder
Item Weight1 Pound
ManufacturerBFG Supply

Pros

  • It’s great if you’re not going out and buying fertilizers specific to different deficiencies.
  • You can use it on most plants.
  • You’ll have enough product for a very long time.

Cons

  • It has equal parts of the various nutrients, which may not be ideal for your plants.
  • Shipment took longer than we had hoped.
Sale
J R Peters
All purpose fertilizer
cucumber leaves

How to treat nitrogen deficiency

Fertilize with nitrogen fertilizer (N fertilizer) with a proper dilution rate and form of nitrogen. Fertilize it weekly with a low-nitrogen & high-potassium fertilizer with an N-P-K ratio of 2-3-6 for container-grown. For soil-grown ones, apply a 20-50 kg/ha of N via side-dressing. Put the fertilizers in a shallow furrow along the side of the crops.

Check your potassium fertilizer to see if your nitrogen is being sufficiently supplied to your plant. You still see symptoms of N deficiency. Excessive potassium can also cause nitrogen deficiency.

Here are some great fertilizers to consider to treat yellow leaves when a lack of nutrients arises.

NameOrganic Tomato & Vegetable Plant Food Fertilizer
Item FormGranular
Item Weight2.25 Pounds
ManufacturerThe Old Farmer’s Almanac
Product Dimensions ‏2 x 7 x 10 inches

Pros

  • We love that it’s organic.
  • It is a great fertilizer for vegetables.
  • It’s done wonders for our vegetables.

Cons

  • Some people have had issues with the delivery. However, we didn’t.
The Old Farmer's Almanac
Good mixture of nitrogen and potassium, excellent for other vegetables as well.

minimal (B), intermediate (C), and severe (D) nitrogen deficiency

Image source: Little, C.R.

Nitrogen-deficient plant

Image source: Haifa

Excessive nitrogen can also cause chlorosis

If the leaves turn yellow despite giving it nitrogen fertilizer, it may be caused by excessive nitrogen. Unlike most plants, they require lower amounts of nitrogen. Overfertilizing it with a high-nitrogen fertilizer will cause more damage than good.

  • SYMPTOMS – Chlorosis will be accompanied by wilting and downward cupping of older parts. Lower ones will exhibit chlorosis next, with brown burnt areas or scorching.

How to treat excessive nitrogen or overfertilizing

To remove excess fertilizer, leach it using freshwater. Use a fertilizer with the proper NPK ratio to fertilize accordingly.

overfertilized (excessive nitrogen)

Image source: Haifa

Potassium deficiency

Unlike most plants that require nitrogen as the bulk of their nutritional requirement, they have high potassium requirements. They’re one of the few plants that need more potassium than nitrogen.

  • SYMPTOMS – Cupping, yellowing, and scorching (appears burnt and brown) manifest in older parts first. Chlorosis starts to occur at the margin, then spreads inwards to the center.
  • REASON – Potassium is an important nutrient for all plants since it plays a major role in a lot of their physiological functions. Some of the many processes that potassium is involved in are the transportation of sugars (food) and growth and metabolism. It also influences the regulation of water balance and protein synthesis. Fruit development and disease resistance are just two other things it helps with.
  • A potassium deficient plant is stunted, with short internodes and small leaves. It exhibits low and abnormal fruit development, sporting brown spots and a spongy-like texture.

How to treat potassium deficiency

Fertilize it properly with the correct ratio of nutrients. Check if you’ve been overfeeding with nitrogen and calcium. Sodium can also be an issue.

These can cause potassium deficiency as well. Their potassium requirements tend to be higher during the flowering stage. Make sure to adjust your fertilizer and schedule according to the growth stage.

Since they need more potassium than nitrogen, the typical K:N ratios are around 1.8:1 and 2.1:1.[3] It will be better for those grown in medium or heavy soils to incorporate potassium nitrate in the soil before you plant. For sandy or well-drained soils, you should do side-dressing of water-soluble potassium fertilizers.[2]

yellowing & scorched leaves of a potassium deficient cucumber

Image source: Haifa

K-deficient cucumber plant with yellow scorched cupped older parts 

Image source: Haifa

Magnesium deficiency

An excessive supply of other nutrients can cause deficiency or lack of uptake of another nutrient. Magnesium deficiency can be caused by excessive potassium, ammonium, or calcium. Like nitrogen, magnesium plays a key role in the production of chlorophyll and photosynthesis.

  • SYMPTOMS – Yellowing of older parts is the main symptom of Mg deficiency. A light tan burn follows it if the deficiency becomes severe.
  • REASON – Magnesium is a major component of chlorophyll. A lack of magnesium severely affects the production of this pigment. As a result, photosynthesis will be affected, and fruit yield will be affected.

How to treat magnesium deficiency

Before planting, use magnesium-rich minerals or water-soluble magnesium nitrate for crops. You can incorporate it as a foliar spray. Examples of magnesium-rich minerals are magnesite and dolomite. Use 300 kg/ha for the former and 800 kg/ha for the latter.[2]

Old leaves of cucumber exhibit chlorosis (left and right) and a light tan burn (right). A young leaf (center) that is not as affected by the magnesium deficiency.

Image source: Haifa

Iron deficiency

Just like nitrogen and magnesium, iron is important in chlorophyll production. Iron deficiencies can be caused by poor drainage, alkaline soil, or high amounts of metallic ions in the soil or water.

  • SYMPTOMS – New/young leaves of magnesium-deficient cucumbers are pale green to yellow. It is followed by scorching or browning due to sunlight if the deficiency becomes severe.
  • REASON – Iron is needed for chlorophyll production. Without enough iron, the production of this green pigment is negatively affected. Iron is also needed for other processes like respiration.

How to treat iron deficiency

Since iron becomes unavailable to plants when the soil is alkaline (above pH 7), you need to correct its pH by acidifying it. Good drainage and aeration in the soil will help your plant’s iron uptake. You can use foliar sprays of iron sulfate at 150 g/100 L [2] or apply iron fertilizers to the soil.

young terminal leaves (at the top) of iron-deficient cucumber showing chlorosis

Image source: Haifa

Phosphorus deficiency

Phosphorus is important in all stages of development, from early growth to developing reproductive organs.

The phosphorus requirement is higher during crop establishment right after transplanting when roots. It’s also important during early growth. Since they continuously produce both vegetative and fruiting parts, they need a steady phosphorus supply.

  • SYMPTOMS – The oldest leaf at the base of the plant turns bright yellow. However, the ones directly above it remain dark green. Brown patches also appear in the old leaves; these will be scorched and spread.
  • REASON – Phosphorus is vital for cellular division and energy transformation. A lack of phosphorus will negatively affect growth.
  • A phosphorus-deficient plant has weak roots and stunted growth. You’ll often find dull gray-green young leaves and low fruit production.
cucumber drink

How to treat phosphorus deficiency

You can solve phosphorus deficiency for crops by fertilizing with a balanced NPK fertilizer or using foliar sprays. You can introduce phosphorus by using a soluble phosphorus source like monopotassium phosphate for the soil.

The oldest part of phosphorus-deficient cucumber is bright yellow, while younger parts remain green in color.

Image source: Haifa

Image source: Haifa

Why are they turning the wrong color?

There are other reasons for chlorosis and leaf scorching besides nutrient deficiency. These color changes may be brought upon by pests or due to a disease caused by an infection. Nutrient deficiencies seldom cause a cucumber leaf to turn white. Still, such symptoms can appear if fungi or other pathogens infect your plant.

white-spotted/colored leaf

Image source: University of Minnesota Extension

Common diseases

Depending on the pathogen or pest infecting your plant, the symptom and treatment will vary. Some diseases are curable, while some are not. For the latter, it is important to let the threat pass or be completely removed before planting again.

VIRAL INFECTION

Viruses can cause your plant to wilt and develop white, yellow, or brown spots on the cucumber leaves.

Cucumber Mosaic – Caused by Cucumber Mosaic Virus (CMV). This can be spread through contact with contaminated tools. However, it is primarily transmitted by aphids that carry the virus once it feeds on the plant.

  • SYMPTOMS – Parts of an infected plant are covered with distinct mosaic (pattern of yellow or green spots and lines) and are curling downwards. The growth is severely stunted, with small leaf sizes and deformed flowers with green petals. Fruits are also discolored and small in size while distorted in shape.

How to prevent mosaic disease

There are no treatments for a CMV infection, but prevention and management can be done.

  • Remove all infected ones immediately and sanitize all your gardening materials thoroughly after every use to avoid spreading the virus.
  • Control the aphid vectors that may infect your plant. If there is an aphid outbreak, treat it with mineral oils or insecticidal soap. Use insecticides with carbaryl and methoxychlor to control pests.
  • Avoid grafting plants. Some may not show symptoms but are still infected by the virus.
  • Grow varieties that are resistant to CMV instead.

cucumber showing CMV infection symptoms

Image source: Scot Nelson on Flickr

cucumber fruits showing CMV infection symptoms

Image source: William Brown on Bugwood.org

FUNGAL INFECTIONS

Fungi can cause your cucumber to wilt and develop white or yellow spots.

Alternaria Blight/Spot is caused by Alternaria cucumerina and is common in areas with warm temperatures and frequent rainfall. This can be spread via fungal spores carried by wind and soil. They can also be carried by water. The fungal spores can survive winter and infect plants once again during spring.

  • SYMPTOMS – Irregular yellow- or brown-colored spots with yellow or green halo appear in older leaves first. These spots expand to become large lesions. As the disease progresses, they will wilt and die.

How to treat and prevent Alternaria blight

  • Fungicides must be used to treat fungal infections. There are a lot of available fungicides, but not all can be applied that produce edible fruits. Consult with your local gardener at a nursery or store which ones can be used so you can still eat the fruits.
  • Remove the infected parts to prevent the spread of the disease. If the whole plant is infected, you must remove it. Treat the soil with fungicide or replace it. Plant a new transplant.
  • Water at the base and avoid getting the top wet – only the soil should be getting wet. Moist and warm areas support the growth of fungi.

symptoms of Alternaria blight

Image source: University of Minnesota Extension

Fusarium Wilt / Cucumber Wilt / Foot-rot– Fusarium oxysporum causes this. It thrives in areas that are warm and moist. This disease is more common in tomato and potato plants, but cucumbers can also be infected.

The fungus targets the root system, restricting its water translocation. It spreads through insects and soil. Water or other contaminated tools may also be the issue. Watering consistently will not save it from dehydration.

  • SYMPTOMS – Stems rot at the base, near the soil line. The leaves turn yellow and develop brown lesions. It will wilt due to the restricted water supply.
man holding cucumbers

How to treat and prevent Fusarium wilt

  • Fungicides must be used to treat fungal infections, such as Mycostop. Use the fungicide according to its instructions, ensuring it reaches the root system.
  • Remove the infected parts to prevent the spread of the disease. If the whole plant is infected, you must remove it. Replace the soil.
  • Use a fungicide-treated seed instead of normal ones.

Image source: Garden.eco

Powdery mildew – This can be caused by Podosphaera xanthii or Erysiphe cichoracearum. This is a common disease among cucurbits. Warm, wet areas favor the growth of the causative fungi. P. xanthii is a more prevalent and destructive cause of powdery mildew.

The spores of these fungi can be spread via insects and wind. The water or soil are places where you wouldn’t expect it, but they can still spread through there. Your tools could be contaminated.

  • SYMPTOMS – Both on the upper and lower surface of the leaves, white powdery spots are formed. As the disease progresses, it will expand into large blotches that can cover the whole leaf and stem.

How to treat and prevent powdery mildew

  • Fungicides must be used to kill fungi. Apply these immediately once you see the symptom manifest. There are other organic treatments that you can use to treat this disease, such as sulfur products. You can also use potassium bicarbonate and baking soda. You can also use vinegar.
  • Remove all infected ones to avoid spreading the disease.
  • Water it at the base and avoid getting the leaves wet. Moist areas favor the growth of the pathogen.
  • Use resistant varieties instead of normal ones.
  • Space them appropriately and use sanitized tools when planting to avoid easy transmission.

Powdery mildew

Image source: University of Minnesota Extension

Downy mildew – This is caused by the fungus-like organism, Pseudoperonospora cubensis.This oomycete was once classified as a fungus, and it thrives in areas that are cool and humid. This can infect other plants via its airborne spores.

  • SYMPTOMS – Leaves have yellow or light green spots on the upper side. The underside has purplish mildew or fuzzy spots. When the disease progresses, lesions will appear, and the leaf will die.

How to treat and prevent downy mildew

  • Fungicides can also be used for downy mildew. Use the fungicide according to its instructions.
  • Remove all infected plants to avoid spreading the disease.
  • Water at the base and avoid getting the leaves wet. Moist areas favor the growth of the pathogen.
  • Space them appropriately and use sanitized tools when planting to avoid easy transmission.

Upperside infected

Image source: University of Minnesota Extension

The underside of an infected leaf

Image source: Integrated Pest Management – University of Missouri

BACTERIAL INFECTIONS

Bacteria can cause your cucumber to wilt and develop white and yellow spots. They can also be brown.

Bacterial / Angular Leaf Spots are caused by Pseudomonas syringae (angular leaf spot) or Xanthomonas campestris. This disease is common in areas that are cool and moist. The disease can be spread through:

  • contaminated insects,
  • water,
  • soil,
  • seeds,
  • or tools.

  • SYMPTOMS:
    • Angular leaf spot caused by P. syringae – Small water-soaked lesions that are angular in shape appear. The bacteria may produce a milky substance that dries into a white crust. Lesions turn reddish-brown with yellow/green edges. As the disease progresses, the lesions will dry and form a hole in the leaf.
    • Bacterial leaf spot caused by X. campestris – Small water-soaked lesions that are circular appear on the underside. Yellow patches or brown spots with yellow edges form.

How to prevent bacterial leaf spots

As of now, there is no effective treatment for this disease. Doing preventive measures will be your key to preventing them from getting infected by bacterial spots.

  • Avoid planting in areas that have been used to grow other cucurbits in the last two years.
  • Water at the base to avoid spreading the bacteria.
  • Space your plants appropriately and use sanitized tools when planting to avoid easy transmission.

cucumber plant suffering from angular leaf spot

Image source: Schwartz, H.F. – Colorado State University

Pests to look out for

Pests can become vectors of viruses, fungi, or bacteria. Pests damage the plant by feeding on the sap and leaves. They won’t leave your flowers or fruits. All these can lead to changes in color or wilting. It can even cause death if left untreated.

APHIDS

Aphids are soft-bodied small insects that suck sap from a plant. You can find these insects on the underside of leaves and stems, where they prefer to feed. These colors differ depending on the species, but the most common ones are yellow or green.

Other colors include brown, pink, red, and black. Common aphid species that infect cucumbers are Myzus persicae (peach aphid) and Aphis gossypii (melon aphid).

  • SYMPTOMS – Heavy aphid infestation causes leaves to turn yellow and distorted, and you’ll see the insects on the underside. It looks like yellow or green spots (the aphids’ bodies). Black or brown necrotic spots appear on the surface, and parts of the plant may feel sticky. It is due to the honeydew that aphids secrete.

How to treat and prevent aphid infestation

  • If the infestation is not severe, you can simply remove the infected parts. Make sure that you prune out all infected areas.
Fiskar shears
  • Use insecticides if the infestation is severe. Other organic treatments are also available such as the use of neem and canola oil.
  • Always check the transplant for any signs of aphid infestation before planting. Make sure they are spaced appropriately.
  • Create a shed or garden bed that can prevent the entry of other pests or animals that can be vectors of diseases.

the underside of a leaf infested with Myzus persicae

Image source: Jim Baker – North Carolina State University

the underside of a leaf infested with Aphis gossypii

Image source: Penn State on Flickr

Cucumber beetles are also worth mentioning because they are common pests that plague the plant. However, these do not change the color of the foliage. These beetles feed on fruits and leaves. They also like stems. Symptoms include wilt and damaged foliage. The presence of larvae and adult insects is another thing to look out for.

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