Well-cultivated squash will be trouble free as long as you protect young plants with a floating row cover to keep out insect pests. Remove the cover when the plants start to flower to allow for pollination. The two pests most likely to attack are squash vine borers and squash bugs.
Squash vine borers, which are most damaging to winter squash, look like 1-inch-long white caterpillars. They tunnel into stems and can go undetected until a vine wilts. Keep a constant lookout for entry holes at the base of the plants, surrounded by yellow, sawdustlike droppings. Cut a slit along afflicted stems and remove and destroy the larvae inside, or inject the stems with Btk (Bacillus thuringiensis var. kurstaki). Hill up soil over the stem wounds to encourage the plant to sprout new roots there.
To prevent borer damage, keep an eye out for the adult borer, a wasplike orange-and-black moth; it lays eggs at the base of the stem in late June or early July in the North, or in April to early summer in the South. During these times, check the base of the stems and just below the surface of the soil regularly for very tiny red-and-orange eggs. Rub the eggs with your finger to destroy them.
Squash bugs are grayish brown bugs up to 3⁄4 inch long; nymphs are similar, but do not have wings. Feeding by adults and nymphs causes leaves to wilt and blacken. Hand pick them and drop them in a container of soapy water. Also destroy their red-brown egg clusters on the undersides of leaves. To trap adults, lay boards on the soil at night; the squash bugs will tend to congregate beneath them, and you can destroy the pests the next morning. Planting radishes, nasturtiums, or marigolds among your squash plants may help repel squash bugs. If plants are heavily infested with young squash bugs, try spraying insecticidal soap or neem as a last resort to save your crop.
Striped and spotted cucumber beetles may also attack squash plants. These 1-inch-long black-headed beetles with green or yellow wings can transmit bacterial wilt as they feed. Since these are spring pests, you can avoid them by planting squash later in the season, when cucumber beetles are less prevalent. Hand pick daily first thing in the morning when the beetles are sluggish. To make the vines less appealing to the beetles, spray them with kaolin clay as often as twice a week.
In most cases, you can avoid squash diseases by choosing resistant cultivars, rotating crops, and choosing planting sites with good air circulation. Here are some diseases to watch for:
Immediately remove and destroy vines afflicted with any of these diseases, or place them in sealed containers and dispose of them with household trash.
Pick zucchini and crookneck cultivars at a tender 6 to 8 inches long; round types are best when they're 4 to 8 inches in diameter. Summer squash will continue setting buds until the first frost, but only if you pick the fruit before it matures°that is, just as its blossom drops off the tip. If you allow even one fruit to mature, the plant's overall productivity may decline. Enjoy summer squash fresh, or preserve them by canning or freezing; they can also be dried, pickled, or turned into relish.
Winter squash will taste bland and watery and won't store well unless you allow them to fully ripen on the vine. Wait until the plants die back and the shells are hard. A light frost can improve the flavor by changing some of their starch to sugar, but it will also shorten their storage life. It's better to pick all ripe fruits before an expected frost and cover any unripe ones with a heavy mulch. You can even carefully gather the vines and fruit close together and protect them with tarps or blankets.
Harvest during dry weather. Use a sharp knife or pruners to cut the fruit from the vine, leaving 2 to 3 inches of stem on the fruit. Pulling the fruit off may damage the stem, and the whole fruit may soon rot from that damaged end. (For that same reason, never carry squash by their stems. If a stem breaks off accidentally, use that fruit as soon as possible.) Clean your harvesting knife between cuts to avoid spreading diseases. Handle squash carefully, because bruised fruit won't keep.
Never wash any winter squash that you intend to store. Dry all types in the sun until the stems shrivel and turn gray; the exception is acorn squash, which doesn't need curing. If placed in a cool, dry area with temperatures of 45° to 50°F and with 65 to 70 percent humidity, winter squash will keep for up to 5 months. Acorn squash needs a slightly cooler and moister storage area.