Winter melon sclerotinia

All vegetables will have diseases, so today I will tell you how to prevent and treat winter melon sclerotinia disease?

Symptoms

Winter melon and wax gourd can be infected in plastic sheds, greenhouses or open fields from the seedling stage to the adult stage. It mainly harms fruits and stems. Fruits are mostly infected in the residual flowers, which first rot in a water-soaked state, and then grow white hyphae, which are tangled into black sclerotia. When stems are infected, faded water-soaked spots appear on the stems near the ground, which gradually expand to brown. Under high humidity conditions, the diseased stems rot softly and grow white cotton-like hyphae. The pith of the diseased stems is damaged, rotten, hollow, or cracked and dried. When petioles, leaves, and young fruits are infected, they are first water-soaked and quickly rot softly, and then grow a large number of white hyphae, which are densely packed to form black mouse-dung-like sclerotia. Leaves and vines above the diseased part wilt and die.

Winter melon sclerotinia

Morphological characteristics of pathogens

The sclerotium is initially white, and then the surface turns black like rat feces. The size varies from 1.1 to 6.5 × 1.1 to 3.5 mm, and it is formed by twisting the mycelium together. Under dry conditions, it survives for 4 to 11 years, and rots in paddy fields after 1 month. At 5 to 20℃, the sclerotium absorbs water and germinates, producing 1 to 30 light brown disc-shaped or flat ascodiscs, which are sexual reproductive organs. The length of the ascodisc handle is adapted to the depth of the sclerotium into the soil, generally 3 to 15 mm, and some can reach 6 to 7 cm. The ascodisc handle extends out of the soil surface as a milky white or skin-colored bud, gradually unfolding into a cup or disc shape. The mature or aging ascodisc turns dark red or light reddish brown. Many asci and lateral threads are produced in the ascodisc. After the ascodisc matures, the ascospores are ejected in a smoke-like manner, up to 90 cm high. The asci are colorless and stick-shaped, and contain 8 colorless ascospores. Ascospores are elliptical, unicellular, and 10 to 15 × 5 to 10 microns in size. Generally, conidia are not produced. In addition to infecting the Cucurbitaceae, it also infects a variety of vegetables such as Solanaceae, Cruciferae, Leguminosae, etc. Mycelium can grow at 0-35℃, and the optimum temperature for mycelial growth and sclerotia formation is 20℃, the highest temperature is 35℃, and 50℃ will kill after 5 minutes.

Transmission routes and conditions of disease onset

Sclerotia are left in the soil or mixed in seeds to overwinter or oversummer. Sclerotia mixed in seeds spread into the field with the sowing of diseased seeds. This disease belongs to the type of conidial airborne disease, which is characterized by the invasion of airborne conidia from parasitic flowers and senescent leaves, and the re-infection of conidia and healthy plants by contact. After invasion, white hyphae grow and begin to harm stigmas or young melons. In the field, male flowers with bacteria fall on healthy leaves or stems and come into contact with hyphae, which can easily cause disease, and repeat infection in this way until conditions deteriorate, and sclerotia fall into the soil or mix with seeds to overwinter or oversummer. It is suitable for the disease to occur in the south from February to April and November to December, and it occurs more in the north from March to May and September to October. This disease has high requirements for water; relative humidity above 85%, temperature between 15 and 20℃ is conducive to sclerotial germination and hyphal growth, invasion and ascocarp production. Therefore, low temperature, high humidity or rainy early spring or late autumn are conducive to the occurrence and spread of the disease, and the sclerotia form in a short time and in large numbers. The disease is more severe in fields where cucurbit, solanaceous and cruciferous vegetables are planted for consecutive years, low-lying land with poor drainage, or excessive nitrogen fertilizer application or frost and freezing damage.

Prevention and treatment methods

Ecological control, mainly by raising the temperature, supplemented by chemical control, can control the spread of pathogens.

(1) Agricultural control. If conditions permit, implement crop rotation with aquatic crops or irrigate the diseased fields for half a month in summer, or deep plow the fields in time after harvest to a depth of 20 cm to bury the sclerotia in the deep layer and inhibit the emergence of the ascocarp. At the same time, adopt formula fertilization technology to enhance parasitic disease resistance.

(2) Physical control: Flood the seeds with 10% salt water 2-3 times before sowing to eliminate sclerotia, or use ultraviolet plastic film in plastic sheds to inhibit the formation of ascocarps and ascospores. You can also use high ridges to cover the ground with mulch to inhibit the emergence of ascocarps and release ascospores to reduce the source of bacteria.

(3) Seed and soil disinfection. Before planting, use 20% methyl tolclofos to make a medicated soil and rake it into the soil. Use 0.5 kg of the drug per 667 m2 and mix it with 20 kg of fine soil. Soak the seeds in 50°C warm water for 10 minutes to kill the sclerotia.

(4) Ecological control. In the morning, the greenhouse should be kept warm to increase the temperature. In the afternoon, ventilation should be provided to remove moisture. After the disease occurs, the night temperature can be appropriately increased to reduce condensation. In early spring, the average daily temperature should be controlled at 29°C or 31°C, and the relative humidity should be lower than 65% to reduce the incidence of the disease. Excessive watering should be prevented. When the soil humidity is high, the watering interval should be appropriately extended.

(5) When ascocarps appear in greenhouses or in the open field, use smoke or spray to prevent and control. Use 15% chlorothalonil smoke or 45% thiophanate-methyl smoke, 250 grams per 667m2, fumigate for one night, once every 8 to 10 days, continuously or alternately with other methods for prevention and control 3 to 4 times; spray 5% thiophanate-methyl dust, 1 kg per 667m2; or spray 50% chlorothalonil wettable powder 1500 times diluted, 50% chloranil or 50% chloranil wettable powder 1000 times diluted; 60% anti-mold superfine powder 600 times diluted, 20% methyl Spray 1000 times diluted chlorpyrifos emulsifiable concentrate, 1500 times diluted 50% thiophanate-methyl wettable powder and 1000 times diluted 70% thiophanate-methyl wettable powder during the flowering period. Spray 60 liters of the mixed solution per 667m2, once every 8 to 9 days, and control continuously for 3 to 4 times. When the disease is serious, in addition to normal spraying, you can also mix the above fungicides into 50 times diluted and apply it to the diseased part of the melon vine, which not only controls the spread but also has a therapeutic effect.

(6) Adding 0.5% and 1% S-H mixture (rice husk, bagasse, shrimp shell powder, silicic acid slag) and urea, superphosphate, potassium nitrate to the soil to make soil additives or adding mineral ash and calcium carbonate to the soil can significantly inhibit the occurrence of sclerotinia disease.