Hazard symptoms: Viral diseases are generally manifested in three types: the first type is mosaic, with yellow-green leaves, some bulges forming bulges, obviously dwarfed plants, small and deformed fruits, and many small bumps on the surface of the fruits. The second type is shriveled, the leaves are usually yellow, the plant internodes are obviously shortened and dwarfed, and the top is shriveled, causing dryness and death. The third type is fern leaf type, in which the leaves and some stems and vines are chicken-claw-like strips and stop growing.

Prevention and control measures: the prevention and control of virus diseases should start with seed collection, and insist on collecting seeds on healthy plants without virus diseases to avoid seeds carrying virus. Before sowing, the seeds can be sterilized by dry heat at 70℃ for three days, or they can be soaked in 10% trisodium phosphate solution for 20 minutes, washed with clear water and then germinated and sown.

Increase the application amount of phosphorus and potassium fertilizer to make the plants grow healthily. Eliminate weeds in and around the melon field and eliminate the intermediate host of virus. When operating in the field, avoid stepping on plant leaves and stems. When pruning, don't pinch off the stems and vines with your hands, but break the branches from the base, and avoid touching the stems and vines left by your hands. In hot and dry weather, we should strengthen the prevention and control of aphids.

Pesticide control: at the initial stage of the disease, 600 times of 20% moroxydine hydrochloride or 800 times of 2% lentinan and other 600 times of azathioprine were sprayed to control aphids. If there are aphids, 70% imidacloprid 7000 times was added for spraying to kill insects.

Pumpkin leaf spot

Harmful symptoms: mainly harmful to leaves. At first, there were small brown spots like water, and yellow halo rings around the spots were visible through sunlight. After the lesion is enlarged, the central part is easy to break, and it is covered with small holes after wind and rain.

Pathogenic conditions and preventive measures: the optimum temperature for development is 25-30℃ and the pH value is 5.8-9.0. The pathogen overwinters in the soil with the diseased plant residues, forming the primary infection source in the next year, or being transmitted through seeds. Prevention: The seeds should be dry-treated at 70℃ for 3 days. Don't bring in sick seedlings, which usually start from the end of April to May and spread after rain. Poor drainage plots and after rainfall or flooding, the disease is more serious. Be careful not to let water droplets stay on the leaves for a long time to prevent water from contributing to the expansion of the disease.

Frost fungus disease of pumpkin

Fungal diseases mainly damage leaves, and the suitable temperature for onset is 20-25 degrees Celsius. At the initial onset, water-stained pale yellow spots appeared on the back of the leaves. With the development of the disease, the spots gradually expanded, and polygonal yellow spots were formed due to the restriction of veins. When the disease is serious, the small spots merge into big spots, and under wet conditions, the gray-brown mold layer grows on the back of the spots. The disease develops from bottom to top, and the whole plant dies in severe cases.

Control methods: ① Select new disease-resistant varieties. (2) Adopt the cultivation technique of high ridge plastic film mulching, re-apply organic fertilizer and topdressing phosphorus and potassium fertilizer to improve the disease resistance of plants. Water should be properly controlled in the early growth stage, and flood irrigation is strictly prohibited after fruiting. Timely pruning, fruit bedding straw to prevent direct contact with the ground. ③ 800- 1000 times solution of 25% metalaxyl wettable powder, or 300 times solution of 40% yishuangling wettable powder, or spraying zineb, mancozeb, copper agent, etc., have good control effect.

Pumpkin powdery mildew

It mainly harms leaves, petioles and stems. When the leaves are infected, white powdery small round spots are produced on the leaves or the back of the leaves at the early stage of the disease, and then gradually expand into irregular white powdery mildew spots, and gradually multiple powdery spots are connected into the whole leaf. The cells and tissues of the diseased leaves do not die after being infected. When the powder layer on the diseased spot is wiped off, the leaves turn green or yellow. At the late stage of the disease, the diseased spot is gray or grayish brown with small black spots (that is, the closed capsule shell of the pathogen). At the end of the disease, the diseased leaf tissue turns brown and dies. The process of stem injury is similar to that of leaves, but there are few dead phenomena in the later stage of disease.

Key points of prevention and control

① Choose disease-resistant varieties according to local conditions. At present, Japanese sweet pumpkin, chestnut pumpkin and orange pumpkin which are widely planted have certain disease resistance, but it is necessary to do a good job of purification and rejuvenation and choose disease-free seedlings.

(2) seed disinfection: before sowing, the seeds should be dried in the sun for 1-2 days to kill epidermal bacteria and improve germination potential; Stir and soak the seeds with warm water at 50-55℃ for 30 minutes, reduce the temperature to 30℃ and continue to soak the seeds for 8- 10 hours, then put in 1% potassium permanganate solution for disinfection for 20-30 minutes, then accelerate germination at 28-30℃ after washing, and sow when it is exposed.

③ Strengthening management: rational close planting, ditching and drainage, timely removal of diseased leaves and old leaves, and strengthening ventilation and light transmission, so as to enhance plant growth, increase the application of phosphorus and potassium fertilizers and improve disease resistance.