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Squash Trouble Before It’s Too Late

These solutions will help to make this your best season yet for growing squash

Fine Gardening – Issue 158
Plan ahead for a healthy crop. Even squash plants that produce a plethora of produce can develop problems. With a little foresight, you can avoid pests and diseases and reap a beautiful bounty, like this.

Green zucchini, yellow crooknecks, and pattypans—all summer squash are tasty, early bearing, and easy to grow, especially if you use good organic methods. But with even the best of crops, things can go wrong. Here are some problems to anticipate and ways to prevent and correct them if they occur.

Why do I have a lot of flowers but not a lot of fruit?

This is perfectly natural with squash plants. Every plant produces male and female flowers, but only females produce fruit. If you peer inside the huge butter yellow trumpets, you’ll see that males have a column of fused anthers, whereas females have a gold-crowned pistil. But the clearest difference is in the stems. Male stems are long and slender; female ones are short, thick, and quick to form a bulb (the beginning of a squash). Sometimes, at first, plants will produce only male flowers or only female flowers, but these will even out.

My leaves are speckled and beginning to blacken. What causes this?

squash bug
Squash bug

This is probably damage caused by the squash bug , an oval gray-brown insect that sucks juices from the leaves and stems. As with any pest, crop rotation is the first line of defense. Avoid planting squash in a spot where it (or its relatives, such as pumpkin, cucumber, and melon) has grown the previous year or two. You can also discourage the overwintering of squash bugs by keeping the garden plot clean of debris where larvae can hide. Search the underside of young leaves for reddish eggs, and rub them off. Pick off and squish or drown the larvae and the adults—a task that is not too daunting with a modest planting (which is usually all you need with squash).

squash blossoms
dead squash blossom

I have fruit that shrivels up and dies on the vine. What should I do?

This problem likely occurs because of inadequate pollination. In the morning, when the flowers are open, look to see if bees are flying in and out of the flowers; if not, there are likely not enough nectar-bearing flowers around to bring in bee traffic. Plant more! I’m partial to native plants, but for early bloom, I’d recommend planting catmint (Nepeta spp. and cvs., USDA Hardiness Zones 3–10), salvia (Salvia spp. and cvs., Zones 3–8), and lavender (Lavendula spp. and cvs., Zones 4–9)—bee magnets all. Keep all insecticides out of your garden, and inspire your neighbors to do the same. Meanwhile, you can hand-pollinate a squash blossom by stroking the anthers of a male flower with a tiny paintbrush or cotton swab, then stroking the top of a female’s pistil to transfer the pollen.

stroke anthers of flower
Stroke the anthers of a male flower with a tiny paintbrush or cotton swab.
fruit dead on the vine
Fruit dead on the vine.

Why does my plant wilt during the day even though it has sufficient water?

squash vine borer
A squash vine borer causes stems to wilt. This nemesis of squash plants can decimate a plant in no time. One telltale sign includes a flattened plant right next to a healthy one. Cut open the stem of the problem plant to locate the culprit.

The squash vine borer could be the culprit here, a cater­pillar that feeds inside a squash plant’s stem, shutting off its water and food supply. To know for sure, look at the base of the stems near the ground for sawdust-like deposits. A last-ditch maneuver is to slit the stem just enough to probe and remove the creature (or creatures). The plant may reroot, carry on with life, and bear fruit if you mound soil over the wounded part of the stem. But if you have recurrent problems with borers, your best bet is to grow extravigorous plants with rich compost; use row covers (until pollination time) to exclude the moths that produce the cater­pillars; and have a series of new, young squash plants coming along as replacements. You might also try one of the vining heirloom Italian summer squashes, such as ‘Zuchetta Rampicante’. These have has solid stems into which no caterpillar may crawl.

My plant has striped bugs all over it. What are they, and what can I do about them?

striped cucumber bug are squash trouble
Cucumber beetle

This pest might be called the striped cucumber beetle, but it likes the whole cucurbit family—squash included—so crop rotation is important here, too. The beetle feeds on all parts of the plant but is even more destructive as a carrier of diseases, namely bacterial wilt and squash mosaic virus. It’s also hard to pick off because it is small and lively. Early in the morning, when it’s heavy with dew, it moves slowly, so you can use a shop vacuum to suction it away; the slot attachment is easiest on the plants. Spreading a well-anchored row cover over the plants will also exclude this and other pests, though it must be removed at flower time to allow pollination.

Is there anything I can do about what looks like mold on my plant?

powdery mildew on plant leaves cause squash trouble
Powdery mildew

If what you see on the leaves is whitish, it’s powdery mildew, a common affliction for many plants in warm, humid weather. If it’s yellowish, then it’s downy mildew, which favors weather that is cool and moist. If either are frequent problems, look for resistant squash varieties when you buy seeds or transplants; then give the plants plenty of air circulation. Some gardeners swear by a solution of milk and water as a foliar spray; baking soda dissolved in water has its fans, too. Remove spent plants promptly.

Growing Squash

The basics for a healthy plant

Grow in your sunniest spot. Squash plants require full sun, at least six hours per day.

yellow squash

Start with great soil. Use fertile, dark, cookie-crumb soil, rich in organic matter. Dig in lots of good compost to help ward off diseases and pests—the healthier the soil, the more resistant plants are to both. Squash also needs trace minerals, so work in a powdered source, like greensand, or top-dress with a liquid seaweed fertilizer.

Plant when the soil has warmed. Squash needs soil that is at least 62°F for direct sowing. Sow several seeds in clusters 2 feet apart, then thin each to the strongest seedling. You can start transplants indoors, but they should be no more than three weeks old when you plant them outside; otherwise, they may be too stretched to develop into a healthy plant.

Provide consistent water. Using a drip line or soaker hose will help keep the foliage dry and disease-free.

Keep plants well weeded. This is especially true when the squash plants are young and have not fully leafed out. The plants might not be able to handle competition from weeds at this stage.

Pick fruit every day or two. This will help keep new, young fruit coming along. Allowing squash monsters to grow slows down production of the crop.

Plant in succession. Plant con­tinually from early summer to midsummer so that you’ll always have fresh, vigorous young fruit that is compact and easy to pick.

Remove finished plants. This will help break pest and disease cycles, and keep the garden free of sprawling vines, which smother nearby crops.

—Barbara Damrosch has written numerous books, including The Four Season Farm Gardener’s Cookbook, coauthored with her husband, Eliot Coleman. Barbara and Eliot operate Four Season Farm in Harborside, Maine.

Photos, except where noted: Danielle Sherry; Scott Phillips; Scott Bauer/courtesy of; Michelle Gervais; Lynn Felici-Gallant; Ann E. Stratton

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