Cucumber diseases & plant problems
What’s happening to my cucumber?
Compare a leaf or fruit below. Each guide explains possible causes, what to check and what you can do next.
A similar-looking photograph is a starting point. Diseases, pests and growing conditions can produce overlapping symptoms; colour alone cannot identify the cause.
Which pattern looks familiar?
Possible disease · powdery mildew
White powder on leaves
White, dusty patches need a closer look. Compare several leaves and both surfaces before choosing a treatment.
Before you decide: White powder on leaves
- Are the patches on the upper surface, underneath, or both?
- Are they spreading across older leaves?
- Has anything recently been sprayed on the plant?
Possible disease · check for downy mildew
Yellow patches between the veins
Turn the leaf over and compare the same patches underneath. Downy mildew and bacterial leaf spots can look similar from above.
Before you decide: Yellow patches between the veins
- Do the veins form the edges of the yellow areas?
- Is there fine grey-purple growth underneath those areas?
- Are several leaves browning quickly, or is the pattern stable?
Possible disease · angular leaf spot
Tan spots and ragged holes
A hole may be what remains of a dry patch. Compare intact spots too; missing tissue alone cannot tell you what caused it.
Before you decide: Tan spots and ragged holes
- Are intact spots bounded by small veins?
- Did the missing tissue start as a tan or wet-looking patch?
- Are stems or fruit marked as well as leaves?
Pest · check for spider mites
Fine pale speckles on leaves
Look beneath several affected leaves with a hand lens. Moving specks and webbing need closer inspection; the pale marks alone do not identify a pest.
Before you decide: Fine pale speckles on leaves
- Are the marks tiny scattered flecks or larger patches?
- Can you see moving specks underneath with a hand lens?
- Is there fine webbing as well as leaf damage?
Symptom · several possible causes
Yellow or mottled leaves
One fading lower leaf and yellowing throughout the plant call for different checks. Water, nutrients, pests and disease can overlap.
Before you decide: Yellow or mottled leaves
- Is it one old leaf or several levels of the plant?
- Are there spots, white patches or distorted new leaves?
- Is the root zone dry, moist or persistently wet?
Establishment problem · check the timing
Wilting just after planting
A newly moved seedling can struggle with moisture, exposure or root disturbance. The time it began matters as much as the droop.
Before you decide: Wilting just after planting
- Did the plant wilt soon after it was moved?
- What is the moisture beside the original root ball?
- Is the stem intact at soil level?
Fruit problem · start with its size
The fruit has turned yellow
A large cucumber left on the vine and a tiny fruit that never grew need different investigations. Check the variety too.
Before you decide: The fruit has turned yellow
- Did a full-sized green fruit turn yellow later?
- Is it a tiny fruit below a spent flower?
- Does the seed packet describe a naturally yellow variety?
Make a useful record.
Photograph the whole plant, both sides of an affected leaf and the stem where it meets the soil. Note when it started, your watering and any recent feed or spray. Keep the plant in place while inspecting it gently.
If the plant is declining quickly or the pattern is unclear, share that record with a local plant clinic, extension service or horticultural adviser. Do not choose a treatment just because the first picture looks close.