Common Squash Diseases and Pests

If you love squash and want to grow your own, there are some common squash diseases and squash pests that you need to be aware of. Preventive measures and effective treatments will enable your squash plants to produce tasty results.

Preventing and Treating Common Squash Diseases

It’s better to prevent squash diseases than to try and eradicate them later. Crop rotation and proper watering are key.
  • Squash diseases and bugs could be waiting in the soil from the year before if you repeatedly plant your crop in the same location.
  • Damaging fungi prefer wet conditions. Watering your plants at their base rather than from above reduces residual moisture and the likelihood of spreading the fungus.

A few of the most common squash diseases that can be avoided by using these techniques are:

Alternaria Leaf Blight

(Alternaria cucumerina)
close up of a leaf infected with alternaria leaf spot showing holes in leaf surrounded by a yellow halo
Description: Causes yellow-brown spots on squash leaves and will eventually cause the leaves to die.

Control: If your plants are affected, removing damaged leaves and applying a fungicide will help to control the problem.

Powdery Mildew

(Podosphaera xanthii or Erysiphe cichoracearum)
large squash plant in a vegetable garden with leaves covered with a white powdery substance resulting from infection with mildew
Description: White powdery mass covering leaves and stems, starting in mid-July through the end of the season and eventually leading to the leaves turning yellow and brown, shriveling and dying.

Control: Plant disease-resistant cultivars. Treat with chemical fungicides as soon as vines start to run, though it is rare for the disease to appear before mid-summer. Don’t crowd plants. Practice strict crop rotation and remove all plant debris. Dispose of it far from your vegetable beds to keep the spores from overwintering.

Fusarium Crown and Foot Rot

(Fusarium solani forma specialis cucurbitae)
wilting squash plant in the garden infected with fusarium crown and foot rot
Description: This fungus first manifests itself as brown or tan spots on squash leaves and will kill the plant within a few days.

Control: Besides proper watering and crop rotation, pre-treating soil with a fungicide before planting can help prevent this fungus.

Bacterial Leaf Spot

(Xanthomonas cucurbitae)
composite image showing bacterial leaf spot on squash leaves and on a pumpkin
Description: Causes lesions on the leaves and blisters on the squash.
Control: Getting a clean start by using new, treated seeds ensures they are free of harmful disease bacteria. Proper watering and crop rotation can also prevent bacterial infections. Treating plants with fungicides can also be an effective treatment for bacterial infections.

Common squash plant pests

Here are some of the bad bugs to watch for along with some tips on dealing with them:

Squash bugs

(Anasa tristis)
close up of a squash bug on a plant
Description: These flat-backed gray insects are difficult to control once they’ve infested your plants.

Control: To kill them, you can fill a bucket with soapy water, pick the bugs off the plants and throw them in. You can also lay boards or shingles on the soil and leave them overnight. Squash bugs will congregate underneath, making them easy to “squash.” Bronze-colored eggs stuck to the underside of leaves are a sign of squash bugs. Smash the eggs before they hatch. Spraying neem oil on your plants will also help to control squash bugs.

Squash vine borers

(Melittia curcurbitae)
composite image showing squash vine borer larvae close up and another image showing the adult insect
Description: Vine borer moths lay eggs around the base of squash plants’ stems. Because they go from being under the soil to inside of the stem, the larvae are hard to detect and can do severe damage before you know they’re there.

Control: Look for eggs around the stems. You may also find some small bore holes there. If you find those signs, your squash plants will likely begin to wilt soon and die shortly thereafter. Get some bacillus thuringiensis (BT) at your garden center or order it online and spray your plants weekly. You can also inject BT into the stems to kill the larvae. Never compost plants infested with vine borers. If possible, burn them to kill any remaining larvae.

Aphids

(Many species in the subfamily Anoeciinae)
composite image showing a close up of aphids and another photo showing the damage they cause to squash plants
Description: These tiny sap-suckers hang out on the underside of squash plant leaves. Check your plants periodically for groups of them, especially if your plants begin to wilt.
Control: Your best bet for controlling these invaders is to encourage beneficial insects to visit your garden and dine on them. Spraying plants with neem oil or insecticidal soap is also effective.

Cutworms

(Agrotis species)
close up photo of a cutworm eating a leaf
Description: These caterpillars come out at night, wrap around the stems of young plants and cut them off at their bases. Fortunately, you can use some easy DIY techniques to stop them.
Control: Slit toilet paper rolls end to end and encircle your young plants with them, pushing them about an inch into the ground to form collars. Or, stick three toothpicks into the ground next to, and around the base of the stems. Either of these methods will prevent cutworms from wrapping around the stems and cutting through them.

Cucumber beetles

(Striped – Acalymma vittata, Spotted – Diabrotica undecimpunctata, Banded – Diabrotica balteata)
composite photo with close ups of striped and spotted cucumber beetles
Description: These squash pests look like yellow ladybugs with black spots or stripes. Not only do they feed on your plants’ leaves and stems, but their larvae also feed on the roots. They can also spread diseases like bacterial wilt.
Control: Spreading straw mulch in your squash bed will draw wolf spiders. They like to hide in straw mulch and feed on cucumber beetles. Also, companion planting some broccoli or radishes can deter cucumber beetles.

Keep Squash Plants Healthy

raised brick vegetable garden bed with big healthy yellow crookneck squash plants
Starting with disease-resistant varieties combined with good cultural and watering practices will go a long way to keeping your squash plants healthy. Strong, well-nourished plants are better able to survive small outbreaks of pests and diseases so you can enjoy a robust harvest. And if you’re growing some buttercup squash, you’ll want to try our creamy, mellow recipe for buttercup squash soup with sage!

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