What’s Wrong With My Squash?

Get the scoop on common squash problems—along with a few tips to make things right.
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©2011, Dorling Kindersley Limited

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Photo By: Photo by Julie A. Martens

Sumptuous Squash

Squash is one of those crops that gives and gives and gives some more. It’s tough to beat the return on investment for a pack of seeds. Choose from summer squash for instant reward, or plant winter squash for fresh-from-the-vine flavors long after the vines are toast. Squash are notoriously easy to grow, but there are a few problems that typically occur. Click through our gallery to diagnose your squash problems—and learn some tips for solving these common issues.

Male Squash Blossom

Squash plants have two different types of blossoms: male and female. Both must be open at the same time for bees to pollinate the female blooms with pollen from the male ones. Male flowers sit atop tall, slender stems. Typically male flowers open first on a squash vine and are joined in about 7 to 14 days by female blooms. Both male and female flowers last for one day. If your squash vine is blooming but no squash are forming, check to see if you have both male and female blooms present.

Female Squash Blossom

Female flowers have a swollen base that resembles a miniature squash. Typically female blossoms nestle against the squash vine stems. This bloom belongs to a butternut squash vine. Female flowers appear about a week or so after male blooms have been opening daily. If both male and female blossoms are present but no squash are forming, check vines early in the day to see if bees are visiting. Spraying pesticides during the day when bees are active can kill bees. Always wait to spray pesticides at dusk, when bees are still.

Mold on Summer Squash

During excessive rainy spells, squash can develop gray mold or botrytis. Most often it occurs when dead blossoms start to rot in rainy weather. If you spot gray mold on fruits, cut the stems and toss them into the compost pile. During prolonged rainy spells, gather fallen blooms if you can easily reach them to reduce the chances of the disease developing.

Blossom End Rot on Squash

Those darken, sunken spots on the very bottom of squash are blossom end rot. It’s so common that veggie growers call it BER for short. It’s not a disease but a symptom of calcium deficiency. It occurs due to uneven watering (wet-dry cycles in soil), too-high nitrogen or root damage. You can eat squash with BER—just cut away the problem area. For a quick fix, treat plants with a calcium spray for BER. Keep soil consistently moist; using mulch helps. Test soil when the growing season ends. Amend as needed.

Wilting Leaves

During midday heat, squash leaves tend to wilt—even though soil may have adequate moisture. Don’t assume that wilted leaves signal dry soil. Always check plants again in the early evening to see if leaves have revived. Squash vines have a lot of leaf area to support, and during the hottest part of the day, it’s common for leaves to wilt. Mulch around the base of vines to help retain soil moisture.

Brown and Crispy Leaf Edges

When young leaves on squash vines develop brown, crispy edges, there’s a good chance you’re looking at pesticide damage. The base of this vine was treated with a pesticide dust to help prevent squash vine borers, but it was applied while plants were too small. This particular vine never grew out of the pesticide damage but remained stunted and didn’t bear any fruit. Use utmost care when applying pesticides and follow label directions exactly.

Gnawed-On Squash

Keep an eye on winter squash, like butternut, which take a long time to ripen fully. If you spy gnawing marks that barely break the skin, you’re probably seeing squirrel damage. These rodents frequently nibble on hard surfaces to keep their front teeth on the short side. During times of drought, squirrels will chew on squash to glean a little moisture. The easiest way to keep squirrels at bay is by wrapping squash in bird netting.

Slug Damage on Butternut

Shallow trails that just break the skin of ripening winter squash are usually the work of slugs. Most often the wounds self-heal. Slipping a piece of broken terra-cotta pot or brick beneath squash can help alleviate slug issues. Dust the ground around ripening squash with limestone dust, crushed eggshells or diatomaceous earth to deter slugs. Or put out slug traps to catch the slimy chewers. Go ahead and cure squash with slug damage, but keep an eye on these fruits in storage—they’re more likely to spoil first.

Squash Vine Borer

When squash vines wilt overnight, the plants have probably been invaded by the dreaded squash vine borer. This insect is the bane of squash gardeners everywhere. The adult insects lay eggs on the base of vines and undersides of leaves. The eggs are tiny red specks—easily visible. Check vines weekly and squish any eggs you see. If vines wilt, yank them up and cut open the stem base to look for borers. Do not put borer-infested vines into your compost. Destroy them.

Squash Vine Borer Holes in Fruit

Squash vine borers can infest a plant so heavily that they’ll tunnel into fruit. Usually the borers work their way into fruit through the stem, but as the growing season winds down, borers will exit vines and burrow directly into fruit. Small holes in the sides of squash are likely a clue that a borer hides inside.

Squash Vine Borer Adult Insect

Adult squash vine borers are red and black flying insects. They hover like bees around the base of squash plants, dabbing eggs onto stems. The surest way to dodge vine borers is using floating row covers over vines during your region’s borer season (which you can learn from your local extension office). Just remember to lift covers so bees can pollinate blooms. You can also dust the base of vines with a very light coating of pesticide dust to deter the insects.

Black Rot Disease on Butternut

Gummy stem blight is a fungus disease that attacks squash. The phase of the disease that attacks fruit is known as black rot. The fungus forms a bronze or corky patch on butternut squash. The disease is only skin deep; the squash flesh is still edible. An infected winter squash won’t store well and so doesn’t develop the rich, sweet flavor these squash are famous for. Still, you can use the squash for soups, roasting or making desserts.

Black Rot Disease Symptoms in Squash

Sometimes winter squash have black rot but show no visible symptoms during the growing or curing phase. Instead, symptoms like wrinkled, puckered skin or raised or ringed spots appear during storage. These squash are still edible; simply cut away any affected portions. Most often the symptoms are only skin deep. Check stored squash weekly to ensure they aren’t developing symptoms.

Powdery Mildew on Squash Leaves

Late in the growing season, a white powdery substance often starts to appear on squash leaves. This is powdery mildew, a fungus disease. Once the disease starts, spraying fungicides controls it, but can’t cure it. Many other plants, including bee balm, lilac and garden phlox, also get powdery mildew and create a source of infection. Homemade prevention strategies, like spraying plants with diluted milk or baking soda, have university research behind them but require faithful application before any mildew appears.

Powdery Mildew Destroys Squash Leaves

As powdery mildew disease progresses, leaves first become completely white, then turn ashen gray. Ultimately, leaf sections between the veins fall away, creating a raggedy appearance. When the growing season ends, pull the squash vines, gathering as much of the infested plant material as you can. Destroy this plant matter; don’t toss it in the compost pile.

Deer Damage on Zucchini

When leaves disappear overnight and you’re left with bare stems, deer are the likely culprits. While they typically avoid eating squash’s prickly leaves and stems, they will chow down on plants early and late in the growing season. Most often they nibble tender new growth. The tell-tale sign of deer damage is ragged and torn leaf edges and jagged stems. Deer lack upper teeth in the front of their mouths, so when they take a bite, they chomp down and yank their heads up, tearing the plant.