What's Wrong With My Squash and Zucchini?

If your squash has succumbed to pests or disease or other problems this season, this is a good time to reflect. Now that you know the challenges, you can learn a few techniques for next time.

Keep Plants Healthy

By now your squash should be a riot of lush, healthy foliage but you need to keep caring for your plants.

1. If you’ve been diligently removing weeds, don’t stop! Remove any weeds that manage to poke through, and top up mulches, using organic matter such as garden compost to help roots stay cool and moist.
2. To keep plants tidy, cut off any dead, shriveled or yellowing leaves, which you’ll start seeing more often.
3. Maintain steady growth by watering very thoroughly whenever its dry – squashes love moist soil and will respond accordingly.

Image: Squash bug and eggs on leaf. Credit: Niney Azman

Watch for Pests

This is the big one! In many countries squash remain relatively free of pests, unless you’re in North America that is, where two troublemakers in particular will often pay an unwelcome visit. 

1. Squash bugs feed on sap, weakening plants and threatening fruit production. Protect plants when they are most active early on in the summer by using row covers or fleece, then continue to check for eggs at least twice a week. Rub or scrape off the eggs. Adult bugs can be knocked or shaken off plants into a bucket of soapy water, or if you keep chickens, offer them as a tasty treat. See our pest page on squash bugs.
2. Squash vine borers are found in the eastern half of North America. They burrow into stems, causing them to rot and foliage to wilt. Like squash bugs they’re most active earlier in summer. Row covers can help keep them off or wrap stems in foil to prevent the adult moths from laying their eggs at the base of plants. It’s possible to cut the grubs out by making vertical cuts into the stem using a sharp knife. Once you’re done, bury the stems with moist soil to encourage new roots. Or try growing butternut squash, which is less likely to be troubled by squash vine borers. Learn more from our squash vine borer article.

Image: Powdery mildew. Credit: AJCespedes

Avoid Powdery Mildew by Regularly Watering

Powdery mildew is common in most regions and is a fungal disease that forms a white,  powdery coating on both sides of the leaves. In the worst cases it will stall growth by preventing the leaves from absorbing enough sunlight.  

A common reason behind powdery mildew is irregular watering. This stresses plants, leaving them susceptible to infection. So keep plants well-watered.

If plants do become infected remove affected foliage straight away. A great way to prevent powdery mildew altogether is to mist leaves with a milky spray.

Milk-Water Spray Solution

1. Make a solution of 1/3 milk to 2/3 water.
2. Spray the milky mixture onto all surfaces, early on a dry, sunny day.
3. Repeat every ten to 14 days throughout the growing season. This milk-water solution can also be used to treat mild infections. 

Learn more about controlling powdery mildew.

See above tips and many more demonstrated in this accompanying video!

Keep Squash from Rotting

Fruits left to swell on the ground can develop blemishes or even rot in wet weather. A simple way to prevent this is to slip a tile or slate under the young fruits as they begin to swell. 

Sprawling varieties of squash look stunning trained up vertical supports such as trellising or arches. Be mindful though that vines can potentially tear or collapse under the weight of heavy fruits. Minimize this risk by tying a sling into place for each fruit. Use any old fabric to make them – old pantyhose or tights, as here, are perfect.

When to Harvest

• Like zucchinis, summer squash are harvested the moment they reach a useable size. Just cut them free and store in the refrigerator for up to a week.
• Winter squash and pumpkins – essentially a type of winter squash – are ready as early autumn passes to mid-autumn. You’ll know they are ready because the skins will have hardened so that they can no longer be scratched or pierced with a fingernail. The stems will also have toughened up and the foliage will be starting to die back.

Storing Winter Squash

Winter squash need to be cured before storing to drive off excess moisture. If it’s dry, just leave squashes and pumpkins where they are, to cure outside in the sunshine. If it’s wet or turning colder, bring them inside to finish curing somewhere warm and dry – on a slatted greenhouse bench, for example. 

Start by cutting back some of the foliage so you can clearly see the fruits. Now cut them free with a sharp pair of pruners, retaining some of the main stem either side to leave a T-shaped stalk. Cup fruits when carrying them; never hold a fruit by its stem or it might snap off, exposing the flesh to infection.

Cured squashes have a very hard, dull skin protecting dense flesh of the most intense flavor. Store them on racks in a cool, dry place, but before you do that, for extra protection you can opt to give the skins a quick wipe over with a mild bleach solution – about one part household bleach to 10 parts water. This serves as a final barrier to rots and molds.

Squash will store anywhere from a month for spaghetti types, to six months for varieties of Hubbard and buttercup squash.

For more information, see our Summer Squash/Zucchini Growing Guide and also our Winter Squash Growing Guide. We also have a guide devoted to growing pumpkins.

What squashes are you growing this summer? How’s it going? Please comment below.