The Ultimate Guide To Cucumber Pests and Diseases


Gardeners face cucumber maladies. They can harm tomatoes and related plants if left untreated. Fungi and microbes attack cucumber leaves, stems, and seeds. Aphids and thrips can spread them via seeds.

In this article, I’ll discuss the most common cucumber diseases and cucumber pests. Therefore, keep reading until the last to get the most useful information about cucumber diseases and pests.

Let’s start.

10 Most common cucumber diseases

diseased cucumber plant leaves with visible spots and discoloration caused by fungal or bacterial infections

There are many different types of cucumber disease but most fall into one of two categories: viral or bacterial infections. Let’s study each of them in detail. 

1: Alternaria Leaf Blight

cucumber leaves with dark spots caused by Alternaria Leaf Blight disease

Cucumbers get Alternaria leaf rot, a fungus illness. Brown marks on leaves and twigs turn dark as the illness advances. Spots may have golden or white edges and fading leaves.

Clean your yard regularly because the fungi overwinter in dirt or trash. If you see these signs in your yard, remove impacted plants quickly. If you’re not sure if they’re sick, don’t discard them! Instead, toss them away with other waste to prevent others from getting sick from eating them.

Related Reading:

2: Anthracnose

cucumber fruits with dark, sunken lesions caused by Anthracnose disease

Fungal anthracnose causes dark spots on cucumber leaves and stems. It also rots and wilts food. Remove affected plants immediately because the illness spreads rapidly.

Anthrax prevention:

  • Don’t put cucumbers in the dirt where they’ve been grown for at least three years because the fungi may still exist.
  • ‘Marketmore’ and ‘Straight Eight’ are plant-resistant. Spring seed stores or garden shops sell them. (plant them indoors). 
  • Keep open-pollinated cucumber seeds separate from other cucumbers to avoid anthracnose from spreading!

3: Leaf spots

cucumber plant leaves with circular brown spots, indicating the presence of leaf spot disease

Cucumber leaves and stems often develop tiny, circular to uneven bacterial leaf spots. Tan, golden, dark brown, or black marks are common. These tumors look like bull’s-eye targets because their cores have a paler rim.

Bacterial leaf spots can live on plant waste and seeds for two years, so if you don’t keep them from expanding, you may see signs year after year.

4: Bacterial Wilt

wilted cucumber plant with yellowing leaves and brown streaks caused by Bacterial Wilt disease

Erwinia tracheiphila causes bacterial wilt. The microbe affects cucumbers, melons, and other Cucurbitaceae plants. (cucumbers, squash, melons). Seedlings, blooms, and food can spread it.

Bacterial wilt causes leaves to turn yellow and die back up the stem and wilt signs on stems above ground. During picking or pruning, the bacterial disease enters plants through stem or tip cuts. Once inside a plant cell, it grows quickly until enough bacteria stop water flow into individual cells, killing them from lack of photosynthetic nutrition.

5: Cucumber Mosaic

Cucumber leaf with mosaic-like patterns caused by Cucumber Mosaic virus disease

The Cucumber mosaic virus causes leaf mottling and deformity. Young leaves turn gray and twisted. The illness can also shrink tomatoes, but it won’t impact their taste or texture.

Cucumber mosaics can be prevented by growing “R”-labeled resistant types. If you grow an affected plant, remove it quickly to prevent its virus-laden sap from infecting nearby plants. (or even wind). Avoid using manure from sick plants in new ones—the disease can live in soil for years!

6: Downy Mildew

cucumber leaves showing signs of Downy Mildew disease, including yellowing, browning, and grayish-white fuzzy patches

The downy fungus affects cucumbers, melons, and squash. Plant leaves and twigs have milky or grayish-green spots. If you live in a hot, muggy climate, try growing cucumbers like ‘Straight Eight’ or ‘Royal Crown’ to avoid downy fungus.

Downy mold is treatable:

  • Remove affected plant parts promptly to avoid disease spread.
  • Spray neem oil every 10 days until signs vanish.

7: Blossom End Rot

 cucumber with Blossom End Rot, showing a dark, sunken lesion on the blossom end of the fruit

Blossom End Rot blackens and kills cucumber stems. It’s most common on cucumbers grown in dusty soil or bad draining, but heat and dryness can also cause it.

Blossom End Rot symptoms:

  • Blackening of the bloom end (bottom) of the fruit, which is often soft and gooey.
  • Fruit with small dark spots.

8: Stem Blight

 cucumber plant stem affected by stem blight disease, showing dark spots and discoloration on the stem surface

Gummy Stem Blight, a fungus illness, impacts cucumbers, melons, and squash. The fungi slow plant growth and make the stem fragile.


  • Plant fronds or twigs with dark spots
  • Wilting leaves that turn gray or brown due to soil moisture or nitrogen deficiency
  • Black-spotted fruit (these are called corky lesions)

Avoiding Gummy Stem Blight:

  • Keep your yard weed-free to reduce food rivalry.
  • Watering routinely keeps the soil wet, preventing fungus growth, which helps avoid this illness.

Related Reading:

9: Bacterial Wilt

cucumber plant leaf with wilting and yellowing caused by bacterial wilt disease."

Squash Bacterial Wilt affects fruits and cucurbits. This illness has similar signs to other cucumber diseases, but they are more severe.

Squash bacterial wilt begins with fading leaves on one side. This wilting will advance until the plant collapses and dies, unlike wilting caused by lack of water or heat stress, which progresses more slowly! If this happens in your yard, quickly remove all diseased plants, dirt, and tools. (such as pruners).

10: Squash Blossom Blight

squash blossom blight disease affecting cucumber plant blossoms with visible discoloration, deformation, and wilted appearance.

Squash Blossom Blight, a fungus illness, affects cucumbers, squash, and fruits. This disease causes wilting leaves and brown-spotted blooms.

Planting hardy plants and weeding your yard will help avoid Squash Blossom Blight. If this illness breaks out in your yard, remove infected plants quickly to prevent germs from spreading.

What Are Common Cucumber Pests? 

Close-up image of cucumber plant leaves with visible signs of pest infestation, including small holes, discoloration, and wilting. Common cucumber pests such as aphids, whiteflies, spider mites, and cucumber beetles may be present on the leaves.

Insects and other creatures known as cucumber bugs can harm cucumber plants, reducing fruit output and quality. In addition to eating the plant’s foliage, stalks, blossoms, and seeds, these parasites can spread illnesses that further endanger the plant. Beetles, aphids, mites, whiteflies, thrips, and squash bugs are typical cucumber parasites. The detection and control of pests correctly are crucial to an excellent cucumber crop.


The cotton aphid, also known as the melon aphid, is the most damaging aphid to melons. Melon bugs vary in size and hue. The mass is 1/16th inch long and ranges from pale yellow to green to black. They have leg joints, cornicles (tailpipes), and dark eyes. 

Aphids usually appear on cucumber plants with stems. Aphids use a style to cut leaves and drink plant fluids. Feeding may curve, crimp, and harden leaves. Colonized plants will turn dark. Aphid honeydew makes leaves shiny. 

Since honeydew gives plants nutrition, sooty mold fungi can coat foliage and fruit with a dark brown growth that is hard to clear and limits photosynthesis.1,2 Melon aphids can spread the cucumber mosaic virus.

Check the undersides of the leaves on the two stems in five regions for aphids. Find natural enemies like ladybugs, syrphids, and lacewings. Aphids on 20% or more stems may require treatment. 

If bugs are localized, try spot treatments. Insecticides harm farms and their natural foes. Herbicides should be used sparingly to avoid disease transmission. Reflective soil repels insects. Late-season sowing should be as far from cucurbit crops as possible.

Cucumber beetles

Striped, spotted, and banded cucumber bugs live on cucumbers. The latter is more common in mild, southern areas. Adult spotted cucumber beetles have craniums, black exoskeletons, eleven black spots on their yellowish-green wing covers, and yellow abdomens. 

Adult striped beetles have blackheads, abdomens, and wings with horizontal yellow bands. Adult banded beetles’ wings have three bright green bands. The young feed on nearby plant roots after hatching from cucumber beetle eggs. 

Adult bugs spread bacterial wilt. Cucumber bugs prefer damp areas in hot weather because they hate heat. Before pollinators arrive, cloth row covers can keep cucumber bugs away. Deep tillage and plant care limit overwintering beetles. Cucumber bug control relies on pesticides. 

Foliar treatments are used when insect numbers reach the action level after pre-plant (soil-applied) or seed-treatment toxins have protected plants for weeks.3 Adult bugs appear soon after growth or moving. After one bug per plant from the orifice to the fourth leaf, start remedies. 



Silverleaf and greenhouse whiteflies are the most dangerous on cucumbers. Avoid treating non-output-reducing whitefly species by accurately identifying them. 

Identifying requires an eye lens. Silverleaf whiteflies keep their wings upright, like a high roof, and don’t join over the back. Greenhouse whiteflies have flattened wings with no obvious orifice where they pass over the back.

Whiteflies live under leaves and eat plant juices. Whiteflies can kill plants by taking too much, reducing their output and economy. Whiteflies, like aphids, create honeydew, which coats plants and supports sooty mold fungi, which lowers food quality and oxygen.

Except for the silverleaf whitefly, pesticides rarely lower whiteflies. Good field hygiene and natural enemy support can usually control whitefly numbers without affecting output or product quality. 


Thrips are tiny, spindly insects with raspy mouthparts. High numbers of plant-grazing species like western flower thrips can harm plants and reduce yields. Western floral thrips eat spider mites, making them potentially helpful.

During blooming season, check plants for thrips harm with yellow sticky traps. Chemicals may be needed if thrips are killing stem ends, blooms, or leaves. Spinosad and other herbicides control thrips. Spinosad, an organic pesticide, gets its active ingredients from the bacteria Saccharopolyspora spinose. Controlling plant numbers reduces thrips.


In conclusion, cucumber plants can be affected by various pests and diseases that can significantly reduce their yield and quality. Common cucumber pests include cucumber beetles, aphids, spider mites, whiteflies, thrips, and squash bugs, while common diseases include bacterial wilt, downy mildew, and powdery mildew

Proper identification, prevention, and management of these pests and diseases are crucial to ensure healthy cucumber plants and optimal yield. Implementing cultural practices such as crop rotation, sanitation, and proper watering and fertilization, along with the use of natural and chemical control measures, can help prevent and manage cucumber pests and diseases.

You May Also Like