Members of the Cucurbita plant genus, pumpkins (Cucurbita maxima), a type of winter squash; and zucchini (Cucurbita pepo), a type of summer squash, are among the easiest plants in the garden to grow, producing flavorful vegetables without a lot of maintenance or intensive labor. As a general rule, pumpkin and zucchini are relatively pest-resistant. However, aphids are common pests in all but the coldest northern climates.
Aphids and Damage
Several aphid types feed on squash and pumpkins, including cowpea aphids, green peach aphids and potato aphids. However, the damage caused by these aphids is usually relatively minor compared to the destruction caused by the melon aphid. Melon aphids, which are smaller than most aphids, are recognizable by a greenish-yellow body and black thorax and head. The pests pierce the leaves to suck out plant juices, resulting in distorted growth, reduced quality and decreased yield. Additionally, the aphids leave honeydew on the fruit. The sweet coating creates an environment conducive to diseases that are often more harmful than the direct damage caused by the aphids.
Insecticidal soap sprays are an effective means of control for aphids and other small, soft-bodied pests. Although insecticidal soap kills aphids and their beneficial predators alike, the damage to beneficial insects is limited because the sprays kill only on contact and have no residual effect. As a result, reapplication is required every four to seven days until the aphids are eliminated. Although you can mix your own insecticidal soap spray, the detergents used in homemade products are harsh and may harm the plants. Insecticidal soap sprays are available in both concentrated and ready-to-use forms.
Neem oil and other horticultural oils, known as foliar oil, summer oil or dormant oil, provide control by smothering aphids. Additionally, the oils help control powdery mildew and other plant diseases. Like insecticidal soaps, oils are safer than pesticides because, although they kill all insects on contact, the products provide no lingering residual effects. Repeat applications are required every seven to 10 days. Do not apply horticultural oils when the temperatures are above 100 degrees Fahrenheit, as the squash and zucchini plants may be damaged. Similarly, avoid use of oils if rain is predicted or if the weather is extremely humid, because wet conditions inhibit effective evaporation of the oils.
Maintain Natural Predators
Many natural predators feed on aphids, including ladybugs and parasitic wasps -- harmless, nonstinging wasps that provide natural control of several harmful insects. The best way to maintain the presence of natural predators in your garden is to avoid use of chemical pesticides. Apply safer, organic controls judiciously, reserving their use for the most heavily affected plants. Always dilute the solution according to label recommendations.