01Yellowing leaves
| Possible cause | Clemson | Wisconsin |
|---|---|---|
| Downy mildew | Clemson Cooperative Extension says small yellow patches show up on top of the leaves first, before the disease spreads any further. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. |
| Squash bug | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says early feeding shows up as small yellow spots scattered on the leaves, which can later turn dry and brown or black along the edges. Source: Squash Bug · checked 2026-09-27 |
02Spots on leaves
| Possible cause | Clemson |
|---|---|
| Anthracnose | Clemson Cooperative Extension says leaf spots start out yellowish or soaked-looking, then get bigger and darken from brown toward black as the infection develops. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 |
| Alternaria leaf spot | Clemson Cooperative Extension says clear rings and edges form around each spot, giving it a bull's-eye look rather than a plain blotch. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 |
| Cercospora leaf spot | Clemson Cooperative Extension says older leaves are hit first, with round to irregular spots that have a paler middle and a darker rim around the edge. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 |
03Curled or distorted leaves
| Possible cause | Clemson | Wisconsin |
|---|---|---|
| Cucumber mosaic virus | Clemson Cooperative Extension says squash plants carrying this virus can look stunted, with leaves that turn blotchy, crinkled, or an unusually pale green rather than their normal color. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | University of Wisconsin–Madison Extension says leaves can cup inward, pucker, or stretch into an odd strap-like shape, while the fruit develops raised, wart-like bumps on its surface. Source: Cucumber Mosaic · checked 2026-09-27 |
04White or powdery coating
| Possible cause | Clemson | Wisconsin | Colorado State |
|---|---|---|---|
| Powdery mildew | Clemson Cooperative Extension says a white, powdery growth spreads across the top of the leaves and onto the stems of affected plants. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | University of Wisconsin–Madison Extension says squash and pumpkin plants are especially likely to lose a lot of leaves once this disease takes hold, more than many other garden plants. Source: Powdery Mildew – Vegetables · checked 2026-09-27 | Colorado State University Extension says of the leaf diseases that turn up on squash, cucumbers, and melons, this powdery-looking one is the most frequent visitor. Source: Cucumbers, Pumpkins, Squash, and Melons · checked 2026-09-27 |
05Sticky leaves or black film
| Possible cause | Clemson |
|---|---|
| Whiteflies | Clemson Cooperative Extension says feeding whiteflies leave behind a sticky residue that drips onto lower leaves and can end up coated in a dark, sooty-looking mold. Source: Cucumber, Squash, Melon & Other Cucurbit Insect Pests · checked 2026-09-27 |
06Holes and chewed leaves
| Possible cause | Clemson |
|---|---|
| Cucumber beetles | Clemson Cooperative Extension says these beetles start feeding as soon as young plants come up, and heavy feeding can kill seedlings outright or badly slow their growth. Source: Cucumber, Squash, Melon & Other Cucurbit Insect Pests · checked 2026-09-27 |
07Insects you can see
| Possible cause | Clemson | Wisconsin |
|---|---|---|
| Cucumber beetles | Clemson Cooperative Extension says one common species is yellowish-green with a black head, black antennae, and 11 black spots running across its back. Source: Cucumber, Squash, Melon & Other Cucurbit Insect Pests · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. |
| Squash bug | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says eggs are usually laid in clusters on the underside of leaves, along the center vein. Source: Squash Bug · checked 2026-09-27 |
| Squash vine borer | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says the adult is a mid-sized, day-flying moth with a wasp-like look, which makes it easy to mistake for a stinging insect. Source: Squash Vine Borer · checked 2026-09-27 |
08Wilting or dying back
| Possible cause | Clemson | Wisconsin |
|---|---|---|
| Bacterial wilt | Clemson Cooperative Extension says vines wilt severely and the whole plant can die soon after. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 | No matching line in the Wisconsin pages we checked. |
| Squash bug | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says heavy feeding can also cause a wilting that looks a lot like bacterial wilt. Source: Squash Bug · checked 2026-09-27 |
| Squash vine borer | No matching line in the Clemson pages we checked. | University of Wisconsin–Madison Extension says the first clue is often plants wilting around midday, because larvae tunneling inside the vine damage the tissue that carries water. Source: Squash Vine Borer · checked 2026-09-27 |
09Stems and canes
| Possible cause | Wisconsin |
|---|---|
| Squash vine borer | University of Wisconsin–Madison Extension says check near the base of a wilting vine for small entrance holes; sawdust-like droppings nearby mean it is worth splitting the stem to look inside. Source: Squash Vine Borer · checked 2026-09-27 |
10Fruit, pods and tubers
| Possible cause | Clemson |
|---|---|
| Cucumber mosaic virus | Clemson Cooperative Extension says fruit from an infected plant can come out an odd shape, with a blotchy or warty surface instead of smooth skin. Source: Cucumber, Squash, Melon & Other Cucurbit Diseases · checked 2026-09-27 |
| Pickleworm | Clemson Cooperative Extension says these caterpillars tunnel into buds and fruit, and sawdust-like waste often pushes out through small holes in the damaged fruit. Source: Cucumber, Squash, Melon & Other Cucurbit Insect Pests · checked 2026-09-27 |
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 Mosaic, University of Wisconsin–Madison Extension (checked 2026-09-27)
- Cucumber, Squash, Melon & Other Cucurbit Insect Pests, Clemson Cooperative Extension (checked 2026-09-27)
- Squash Bug, University of Wisconsin–Madison Extension (checked 2026-09-27)
- Squash Vine Borer, University of Wisconsin–Madison Extension (checked 2026-09-27)