01Yellowing leaves
| Possible cause | Clemson |
|---|---|
| Downy mildew | Clemson Cooperative Extension says look for small yellow patches on the top of the leaf when this disease is just starting, before it spreads any further. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 |
02Spots on leaves
| Possible cause | Clemson | Wisconsin | Colorado State |
|---|---|---|---|
| Angular leaf spot | No matching line in the Clemson pages we checked. | No matching line in the Wisconsin pages we checked. | Colorado State University Extension says of the diseases that hit cucumber, this bacterial one turns up most often; it forms lesions with straight, angular edges on the leaves and can also affect the fruit. Source: Cucumbers, Pumpkins, Squash, and Melons · checked 2026-09-27 |
| Cucumber mosaic virus | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says leaves and fruit can show blotchy white, yellow, and light-green mottling along with ring-shaped spots of discolored tissue. Source: Cucumber Mosaic · checked 2026-09-27 | No matching line in the Colorado State pages we checked. |
| Downy mildew | Clemson Cooperative Extension says lesions expand and turn brown with ragged, irregular edges as the disease moves along. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. | No matching line in the Colorado State pages we checked. |
03Curled or distorted leaves
| Possible cause | Clemson | Wisconsin |
|---|---|---|
| Powdery mildew | Clemson Cooperative Extension says leaves in the affected areas can look stunted and distorted, and some may drop from the plant earlier than they should. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. |
| Squash mosaic virus | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says cucumber beetles can also spread this virus, which leaves plants stunted with distorted, blotchy-colored leaves. Source: Cucumber Beetle · checked 2026-09-27 |
| Melon aphids | Clemson Cooperative Extension says leaves attacked by these aphids curl downward and can eventually turn brown and die. Source: Cucumber, Squash, Melon & Other Cucurbit Insect Pests · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. |
04White or powdery coating
| Possible cause | Clemson | Wisconsin |
|---|---|---|
| Powdery mildew | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says the coating looks as if the leaves were dusted with talcum powder or powdered sugar. Source: Powdery Mildew – Vegetables · checked 2026-09-27 |
| Downy mildew | Clemson Cooperative Extension says on cucumber, this disease shows up as a spore layer on the underside of the leaves, a place worth checking when this is suspected. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. |
05Sticky leaves or black film
| Possible cause | Clemson |
|---|---|
| Whiteflies | Clemson Cooperative Extension says as whiteflies feed, sticky honeydew drips down onto the lower leaves, which can end up blackened with a sooty-looking mold. Source: Cucumber, Squash, Melon & Other Cucurbit Insect Pests · checked 2026-09-27 |
06Holes and chewed leaves
| Possible cause | Wisconsin |
|---|---|
| Cucumber beetles | University of Wisconsin–Madison Extension says the larvae chew on plant roots and stems, which can stunt or wipe out seedlings and transplants once numbers build up. Source: Cucumber Beetle · checked 2026-09-27 |
07Insects you can see
| Possible cause | Clemson | Wisconsin |
|---|---|---|
| Bacterial wilt | Clemson Cooperative Extension says striped or spotted cucumber beetles carry this disease from plant to plant as they feed, so beetle activity is worth watching for. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. |
| Cucumber beetles | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says the striped form is small and yellow-green, marked with three black stripes running down the length of its body. Source: Cucumber Beetle · checked 2026-09-27 |
08Wilting or dying back
| Possible cause | Clemson |
|---|---|
| Bacterial wilt | Clemson Cooperative Extension says this disease hits cucumber and cantaloupe the hardest, causing more damage on those two crops than on squash, pumpkin, or watermelon. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 |
09Stems and canes
| Possible cause | Clemson |
|---|---|
| Gummy stem blight | Clemson Cooperative Extension says this fungal disease attacks the stems and leaves of cucumber along with a few other cucurbits, and is caused by a specific fungus. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 Clemson Cooperative Extension says as it advances, stems can split open into wound-like cankers, sometimes with a brown, gummy substance visible on the surface. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 |
10Fruit, pods and tubers
| Possible cause | Clemson | Wisconsin | Colorado State |
|---|---|---|---|
| Poor pollination | No matching line in the Clemson pages we checked. | No matching line in the Wisconsin pages we checked. | Colorado State University Extension says fruit can come out an odd shape when pollination is incomplete, which can happen if bee activity is too low. Source: Cucumbers, Pumpkins, Squash, and Melons · checked 2026-09-27 |
| Cucumber beetles | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says beetles feeding directly on the fruit can leave cosmetic blemishes that make cucumbers less appealing to sell, even though the fruit is otherwise fine. Source: Cucumber Beetle · checked 2026-09-27 | No matching line in the Colorado State pages we checked. |
| Squash mosaic virus | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says fruit from an infected plant can come out misshapen and blotchy in color, along with a smaller overall harvest. Source: Cucumber Beetle · checked 2026-09-27 | No matching line in the Colorado State pages we checked. |
| Pickleworm | Clemson Cooperative Extension says on cucumber, this caterpillar tunnels into the fruit, and sawdust-like droppings often push out through small holes in the damaged fruit. Source: Cucumber, Squash, Melon & Other Cucurbit Insect Pests · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. | No matching line in the Colorado State pages we checked. |
What to do about it. This site only covers how to recognize a problem. For what to do next, open the Extension page linked in the row: their advice is written for their region and is kept up to date by them.
Pages compared on this chart
- Cucumber, Squash, Melon & Other Cucurbit Diseases, Clemson Cooperative Extension (checked 2026-09-27)
- Powdery Mildew – Vegetables, University of Wisconsin–Madison Extension (checked 2026-09-27)
- Cucumbers, Pumpkins, Squash, and Melons, Colorado State University Extension (checked 2026-09-27)
- Cucumber Beetle, University of Wisconsin–Madison Extension (checked 2026-09-27)
- Cucumber Mosaic, University of Wisconsin–Madison Extension (checked 2026-09-27)
- Cucumber, Squash, Melon & Other Cucurbit Insect Pests, Clemson Cooperative Extension (checked 2026-09-27)