Cucumber Leaves Turning Yellow or Brown? Diseases, Pests, & Problems

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

boy eating cucumber

Cucumbers (Cucumis sativus) are sun- and water-loving plants since these are native to sub-tropical regions. Cucumbers 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 cucumber plant may be wilting, its leaves turning yellow, white, or brown, or has black or white spots on its leaves, ruining the chances of your cucumber plant to set fruit. To help you have a bountiful harvest, we’ll enumerate some of the most common reasons behind these issues, along with their respective treatment and precautions.

wilting and yellowing cucumber leaves

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

Cucumber Plant Diseases, Pests, and Problems

There are a lot of diseases, pests, and external factors that can cause a loss of yield in cucumbers. If you noticed your cucumber plants wilting and developing spots or different leaf color, even though you’ve given them enough amount of sun, water, and nutrients, then you might need to check for diseases and pests. It’s important to quickly determine the cause behind the symptoms your plants are experiencing because a pathogen or pest infestation may quickly spread and destroy your crop.

Why are my cucumber leaves turning yellow / brown?

Abnormal leaf yellowing is called chlorosis, which happens when the leaf lack chlorophyll, an essential green pigment for the plant’s survival. This can be caused by damaged roots, poor drainage, nutrient deficiency, or high soil pH. However, other symptoms that accompany leaf yellowing, such as browning (scorched leaf) wilting, lesions, brown or black spots, may be caused by diseases or pests.

yellowing cucumber leaves

Image source: Garden.eco

Cucumber leaves turn yellow if overwatered

The most common sign of overwatering is leaf yellowing; leaves appear limp, stunted, and yellow. Roots become damaged and unable to absorb nutrients when the soil around it 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, your plant will also suffer from nutrient deficiency, leading to chlorosis.

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

overwatered cucumber plant

Image source: Stack Exchange


Nutrient deficiency causes leaf yellowing (and browning)

Depending on the type of nutrient deficiency, the appearance of chlorosis (leaf yellowing) will be different in terms of where it manifests in the leaves (old or young leaves).

Nitrogen deficiency can cause leaf yellowing

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

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

How to treat nitrogen deficiency in cucumber plants

Fertilize your cucumber plants with nitrogen fertilizer (N fertilizer) with a proper dilution rate and form of nitrogen. For container-grown cucumber plants, fertilize the plant weekly with a water-soluble, low-nitrogen, high-potassium fertilizer with an N-P-K ratio of 2-3-6.[1] For soil-grown cucumber plants, apply a 20-50 kg/ha of N via side-dressing [2] (putting fertilizers in a shallow furrow along the side of the crops).

If your nitrogen is being sufficiently supplied to your plant but you still see symptoms of N deficiency, check your potassium fertilizer. Excessive potassium can also cause nitrogen deficiency in plants.

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

Image source: Little, C.R.

cucumber fruit from a nitrogen-deficient plant

Image source: Haifa

Excessive nitrogen can also cause chlorosis

If your cucumber plant’s leaves are turning yellow despite giving it nitrogen fertilizer, it may be caused by excessive nitrogen instead. Unlike most plants, cucumbers require lower amounts of nitrogen, and 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 leaves. Lower leaves will exhibit chlorosis next, with brown burnt areas or leaf scorching.

How to treat excessive nitrogen or overfertilizing in cucumber plants

To remove excess fertilizer, leach it using fresh water. Use a fertilizer with the proper NPK ratio for your cucumber plants and fertilize accordingly.

overfertilized (excessive nitrogen) cucumber plant

Image source: Haifa

Potassium deficiency can cause leaf yellowing and browning

Unlike most plants that require nitrogen as the bulk of their nutritional requirement, cucumbers have high potassium requirements, one of the few plants that needs more potassium than nitrogen.

  • SYMTOMS – Cupping, yellowing, and scorching (appears burnt and brown in color) manifests in older leaves first. Chlorosis starts to occur at the leaf margin, then spreads inwards to the center of the leaf.
  • 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 transportation of sugars (food), plant growth and metabolism, regulation of water balance, protein synthesis, fruit development, and disease resistance, among many others.
  • A potassium deficient plant is stunted, with short internodes and small leaves, and exhibits low and abnormal fruit development, sporting brown spots and spongy-like texture.

How to treat potassium deficiency in cucumber plants

Fertilize your cucumber plants properly with the correct ratio of nutrients. Check if you’ve been overfeeding your plants with nitrogen, calcium, or sodium because these can cause potassium deficiency, too. During the flowering stage of cucumbers, their potassium requirements tend to be higher, so make sure to adjust your fertilizer and schedule according to the stage of growth your plant is in.

Since cucumbers need more potassium than nitrogen, the typical K:N ratios are around 1.8:1 and 2.1:1.[3] For cucumbers grown in medium or heavy soils, it will be better 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 leaves (L)

Image source: Haifa

Magnesium deficiency can cause leaf yellowing and browning

As mentioned, 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. Just like nitrogen, magnesium plays a key role in the production of chlorophyll and photosynthesis.

  • SYMPTOMS – Yellowing of older leaves is the main symptom of Mg deficiency. It is followed by a light tan burn if the deficiency becomes severe.
  • REASON – Magnesium is a major component of chlorophyll; thus, lack of magnesium severely affects the production of this pigment. As a result, photosynthesis will be affected, and fruit yield will be low.

How to treat magnesium deficiency in cucumber plants

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

old leaves of cucumber exhibiting chlorosis (left and right) and a light tan burn (right), and a young leaf (center) that is not as affected by the magnesium deficiency

Image source: Haifa

Iron deficiency can cause leaf yellowing and browning

Just like nitrogen and magnesium, iron is important in the production of chlorophyll. 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, and without enough iron, production of this green pigment is negatively affected. Iron is also needed for other processes like plant respiration.

How to treat iron deficiency in cucumber plants

Since iron becomes unavailable to plants (e.g., they cannot utilize it because it becomes insoluble) when the soil is alkaline (above pH 7), you need to correct the soil’s pH by acidifying it. Also, good drainage and aeration in soil will help your plants in the uptake of iron. For crops, 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 can cause leaf yellowing and browning

Phosphorus is important in all stages of plant development, from early plant growth up to the development of reproductive organs, such as flowers, fruits, and seeds. During crop establishment (i.e., right after transplanting when roots are still being established) and early plant growth, the phosphorus requirement of plants is higher. Since cucumbers continuously produce both vegetative and fruiting parts, they need a steady supply of phosphorus.

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

How to treat phosphorus deficiency in cucumber plants

For planted crops, you can solve phosphorus deficiency by fertilizing with a balanced NPK fertilizer or you can use foliar sprays. For soil, you can introduce phosphorus by using a soluble phosphorus source like mono potassium phosphate. [2]

oldest leaf of phosphorus-deficient cucumber is bright yellow, while younger leaves remain green in color

Image source: Haifa

phosphorus deficient plant (L) has stunted growth and dull gray-green leaves

Image source: Haifa

Why are my cucumber leaves turning white / yellow / brown?

As mentioned, 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 bacterial, viral, or fungal infection. Nutrient deficiencies seldom cause a leaf to turn white, but such symptom can appear if your plant is infected by fungi or other pathogens.

white spotted/colored leaf of a diseased cucumber plant

Image source: University of Minnesota Extension

Common cucumber diseases that turn leaves yellow/brown/white

Depending on the pathogen or pest that is 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 cucumber plant to wilt and develop white, yellow, or brown spots.

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

  • SYMPTOMS – Leaves of an infected plant are covered with distinct mosaic (pattern of white, yellow, or green spots and/or lines) and are curling downwards. The plant’s growth is severely stunted, with small leaf size and deformed flowers with green petals. Fruits are also discolored (same as the leaves), distorted in shape, and small in size.

How to prevent cucumber mosaic disease

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

  • Remove all infected plants 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 cucumber plants. Some plants may not show symptoms but are still infected by the virus.
  • Plant cucumber varieties that are resistant to CMV instead.

cucumber leaf 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 plant to wilt and develop white, yellow, or brown spots.

Alternaria Leaf Blight/Spot – This is caused by Alternaria cucumerina and is common in areas with warm temperatures and frequent rainfall. This can be spread via fungal spores that are carried by wind, soil, or 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, and then these spots expand to become large lesions. As the disease progresses, the leaves will wilt and die.

How to treat and prevent Alternaria leaf blight

  • Fungicides must be used to treat fungal infections. There are a lot of available fungicides, but not all can be applied to plants 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 of your cucumbers.
  • 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 better yet, replace it), and plant a new transplant.
  • Water your plants at the base and avoid getting the leaves wet. Moist and warm areas support the growth of fungi.

symptoms of Alternaria leaf blight

Image source: University of Minnesota Extension

Fusarium Wilt / Cucumber Wilt / Foot-rot– This is caused by Fusarium oxysporum. 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 of the plant, restricting its water translocation. It spreads through insects, water, soil, and other contaminated tools. Watering consistently will not save your plant from dehydration.

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

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, making sure that 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, treat the soil with fungicide (or better yet, replace it), and plant a new transplant.
  • Plant a fungicide treated seed instead of normal ones.

yellowing and wilting leaves with lesions in some areas

Image source: Garden.eco

Powdery mildew – This can be caused by Podosphaera xanthii or Erysiphe cichoracearum. This is a common disease among cucurbits, and 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 insect, wind, water, soil, or contaminated tools.

  • SYMPTOMS – Both on the upper and lower surface of the leaves, white powdery spots are formed, which, as the disease progresses, 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. However, there are other organic treatments that you can use to treat this disease, such as sulfur products, potassium bicarbonate, baking soda, and vinegar.
  • Remove all infected plants to avoid spreading the disease.
  • Water your plants at the base and avoid getting the leaves wet. Moist areas favor the growth of the pathogen.
  • Plant resistant varieties instead of normal ones.
  • Space your plants appropriately and use sanitized tools when planting to avoid easy transmission.

infected cucumber plant showing symptoms of 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, while the underside of the leaves have purplish mildew (sporangia of the pathogen) or fuzzy, dark gray or purple 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 your plants at the base and avoid getting the leaves wet. Moist areas favor the growth of the pathogen.
  • Space your plants appropriately and use sanitized tools when planting to avoid easy transmission.

Upper side of an infected leaf

Image source: University of Minnesota Extension

Underside of an infected leaf

Image source: Integrated Pest Management – University of Missouri

BACTERIAL INFECTIONS

Bacteria can cause your cucumber plant to wilt and develop white, yellow, or brown spots.

Bacterial / Angular Leaf Spots – This is 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 on the leaves, and the bacteria may produce milky substance that dries into a white crust. Lesions turn reddish-brown in color with yellow/green edges, and 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 in shape appear at the underside of the leaves. Yellow patches or brown spots with yellow edges form on the leaves.

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 avoid your plants from getting infected by bacterial leaf spots.

  • Avoid planting in areas that have been used to grow other cucurbits in the last two years.
  • Water your plants 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

Cucumber pests that can turn your leaf yellow/brown/white

Pests can become vectors of viruses, fungi, or bacteria. Also, pests damage the plant by feeding on the plant’s sap, leaves, flowers, or fruits. All these can lead to changes in the leaf color, wilting, or death of plant if left untreated.

APHIDS

Aphids are soft-bodied small insects that suck sap from a plant. You can find these insects at the underside of leaves and stems, where they prefer to feed. The colors of these differ depending on the species, but the most common ones are yellow or green in color (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 of the leaf, which looks like yellow or green spots (the bodies of the aphids themselves). Black or brown necrotic spots appear on the surface of the leaves, and parts of the plant may feel sticky 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.
  • 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, and make sure your plants 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. See the last section of the article for some of our recommended tools for building sheds, garden beds, and fences.

underside of a leaf infested with Myzus persicae

Image source: Jim Baker – North Carolina State University

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 of cucumbers. However, these do not change the color of the foliage. Cucumber beetles feed on fruits, leaves, and stems, so symptoms will be wilt, damaged foliage, and the presence of larvae and adult insects.

Easy plants to grow for beginners

If your cucumber plants kept on getting various diseases, whether due to the soil or abundance of pests in your area, and you’ve given up on cultivating cucumbers, we hope that your interest in gardening hasn’t wilted yet. We suggest that you try growing these plants instead, for hassle-free upkeep:

  • Sansevieria or snake plants – These plants can be grown indoors or outdoors. Snake plants are one of the easiest plants to take care of because they can survive with moderate to low light and seldom need watering. These plants can improve the air quality in your home by removing toxic gases in the air (they were featured in a NASA clean air study). Read this article to know about the dos and don’ts on taking care of snake plants, where you can also find a list of Sansevieria varieties to choose from. There are varieties that can fit nicely on your desk, growing up to only 6 inches high!

Image source: Plants Bank on Pinterest

  • Dwarf shrubs – These are also hassle-free outdoor plants that only need minimum maintenance. Even if you only have a small or narrow strip of land at your home, these dwarf shrubs will surely be able to grow well, giving you a breath of fresh air and beautiful visuals of their bloom or foliage.

Image source: fast-growing-trees.com

  • Purple flowers – If you want to try growing flowering plants, then we have a great suggestion for you: check this article where we provided a list of plants that will give you a beautiful purple bloom. Check out this article on planting seeds, and this one that includes various gardening terms, too.

Image source: Botanical Interests

Handy tools for seasoned gardeners

If you have a growing business, then expanding your nursery might be on your next agenda. To help you with your business endeavors, we’ll provide you a list of tools that will surely be of help to you.

  • Fuel transfer tanks – These tanks can be used as a reservoir for water, fertilizer, and gasoline. Check them out here.

  • Plasma cutters – If you work with a lot of different materials for your garden, from steel to brass, then you might want to invest in a plasma cutter that can easily cut materials (stainless steel, aluminum, brass, copper, and conductive materials) with high precision. Check out the best plasma cutters here.

  • Wide belt sanders – If poor woodwork has been bothering you, and you want only the best materials for your shed, then you should check out wide belt sanders here. These provide a high-quality finish to wooden surfaces and adjust the wood’s thickness according to your requirements.

  • MIG welders – In business, it’s important to be able to produce products fast without compromising quality. If you want a welding tool that produces high-quality welds in a timely manner compared to other tools, then check out these MIG welders here.

  • Engine-driven welder – However, if you’re looking for portable welders, take a look at this list of engine-driven welders that you can operate anytime, anywhere.

  • Waste oil heaters – Plants need their environment to be at a certain temperature range to thrive. During winter, we’re sure that your bill ramps up a ton due to the heaters that you have to use to keep your plants from dying in the nursery or in your home. If this is an issue for you, then you might want to check out the best waste oil heaters here. Instead of simply discarding oil that you no longer use, you can use it instead to fuel waste oil heaters for an eco-friendlier practice.

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References:

  1. Asher, B. (2020). What is the best fertilizer for cucumbers. Retrieved from https://www.hunker.com/13427375/what-is-the-best-fertilizer-for-cucumbers
  2. Haifa. (n.d.). Crop Guide: Nutrients for Cucumber. Retrieved from https://www.haifa-group.com/cucumber-0/crop-guide-nutrients-cucumber
  3. Raudales, R. & McAvoy, R. (n.d.). The role of potassium in cucumber plants. Retrieved from https://www.hortibiz.com/news/?tx_news_pi1%5Bnews%5D=27321&cHash=ab46266c78d20da35bd2a9ceb19efa33#:~:text=Potassium%20plays%20a%20key%20role,is%20a%20highly%20mobile%20element

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