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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases |
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 page, read 2026-09-27: Cucumbers, Pumpkins, Squash, and Melons |
| 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 page, read 2026-09-27: Cucumber Mosaic | 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Cucumber Beetle |
| Melon aphids | Clemson Cooperative Extension says leaves attacked by these aphids curl downward and can eventually turn brown and die. Source page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Insect Pests | 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 page, read 2026-09-27: Powdery Mildew – Vegetables |
| 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Insect Pests |
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 page, read 2026-09-27: Cucumber Beetle |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Cucumber Beetle |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases |
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 page, read 2026-09-27: Cucumbers, Pumpkins, Squash, and Melons |
| 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 page, read 2026-09-27: Cucumber Beetle | 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 page, read 2026-09-27: Cucumber Beetle | 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Insect Pests | 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
- 2026-09-27 · Cucumber, Squash, Melon & Other Cucurbit Diseases, Clemson Cooperative Extension
- 2026-09-27 · Powdery Mildew – Vegetables, University of Wisconsin–Madison Extension
- 2026-09-27 · Cucumbers, Pumpkins, Squash, and Melons, Colorado State University Extension
- 2026-09-27 · Cucumber Beetle, University of Wisconsin–Madison Extension
- 2026-09-27 · Cucumber Mosaic, University of Wisconsin–Madison Extension
- 2026-09-27 · Cucumber, Squash, Melon & Other Cucurbit Insect Pests, Clemson Cooperative Extension