squash pests and diseases
Summer squash is relatively easy to grow, but there are many pests and diseases that can affect plants. Early control of the following pests, especially cucumber beetles, can be best achieved by keeping the crop with a floating row lid installed at the time of planting. Keep it until the plants start to bloom, then remove it to allow for pollination. Mode-weight array covers, such as Agribon's AG-19, provide additional heat for rapid growth and frost protection up to about 28 F. To reduce pest and disease stress, avoid planting other cucumbers such as melons, winter squash, or pumpkins grown in the last three years. For assistance with pests not discussed below, contact your local co-operative extension service.
Insects
Cucumber beetles can destroy small seedlings or transplants and cause significant forage damage even on full-size plants. If that is not enough, these beetles will transmit bacterial wilt and squash mosaic virus to your squash plants. Two species commonly encountered - the striped cucumber beetle (left) and the spotted cucumber beetle (right). Control them with line covers or naturally approved pesticides such as AsaGuard, Mucotrol ESO, kaolin clay (Surround WP), or PyGanic.
Squash flag borers are moth larvae that burrow into plant stems, causing the leaves and vines to wither and eventually die. Control these pests by looking for worm and larval entrances at the base of the vines. Open the stems to confirm the presence of larvae and then kill them. If the injured stems are buried, they can take root again. If there are larvae, apply biconic acid directly on the crown and vines of the plant.
Squash bugs can be very harmful to small plants, but in large numbers, they can be very harmful to large plants. Gray-brown adults use their perforated mouth areas to absorb sap from plants, with fruit scars and leaf wilt. Females lay brown eggs at the base of squash leaves. Nymphs, which usually hatch in groups, have a light green belly that darkens as they mature. Control them with row covers or destroy eggs, nymphs, and adults. Nymphs can be controlled with safe insect repellent; PyGanic works well against adults and nymphs.
diseases
The powdery mildew usually begins to develop in late summer and continues into the fall. Affected leaves show powdery white spots on both sides of leaves and stems. Severe infections compromise the plants, causing early maturation of the leaves and premature and incomplete ripening of the fruit. Many naturally approved products, including fungicides, can be used to control powdery mildew.
Cucumber mosaic, zucchini yellow mosaic, watermelon mosaic 1, and watermelon mosaic 2 (also known as "papaya ringspot") are viruses that infect summer squash. Aphids usually transmit these diseases from other vegetable crops or weeds. It is difficult to distinguish them because their symptoms are similar. Affected leaves may show distorted yellowish mosaic patterns. Affected fruits are mossy, discolored, and malformed. These viruses have no controls, so the best way to avoid them is to plant resistant varieties. It also helps control pests and weeds in the area around your garden well. Leaf specimens can be tested by your local cooperative extension service to determine which viruses infect your crop.
Bacterial wilt is best avoided by controlling the cucumber beetles that spread the disease. The leaves of the affected plants wither and then turn yellow between the leaf veins and eventually turn brown and die. There is no treatment once the plants are affected. Affected plants should be removed and buried or put in a bag and put in the trash.
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