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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Squash Bug |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases |
| 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases |
| 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Cucumber Mosaic |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Powdery Mildew – Vegetables | 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 page, read 2026-09-27: Cucumbers, Pumpkins, Squash, and Melons |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Insect Pests |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Insect Pests |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Insect Pests | 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 page, read 2026-09-27: Squash Bug |
| 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 page, read 2026-09-27: Squash Vine Borer |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases | 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 page, read 2026-09-27: Squash Bug |
| 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 page, read 2026-09-27: Squash Vine Borer |
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 page, read 2026-09-27: Squash Vine Borer |
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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Diseases |
| 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 page, read 2026-09-27: Cucumber, Squash, Melon & Other Cucurbit Insect Pests |
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 Mosaic, University of Wisconsin–Madison Extension
- 2026-09-27 · Cucumber, Squash, Melon & Other Cucurbit Insect Pests, Clemson Cooperative Extension
- 2026-09-27 · Squash Bug, University of Wisconsin–Madison Extension
- 2026-09-27 · Squash Vine Borer, University of Wisconsin–Madison Extension