Symptoms of Sclerotinia Rot in Hami Melon and Its Control Methods
Everyone knows that Hami melons produced in Xinjiang are large and sweet, because they receive a relatively long period of sunlight. However, delicious Hami melons are no longer only available from Xinjiang; they are now grown in various places. During the cultivation of Hami melons, diseases may attack for a number of reasons, especially Sclerotinia rot, which affects both the yield and the quality of Hami melons. So what are the symptoms of Sclerotinia rot in Hami melon? What are the control methods?
I. What are the symptoms of Sclerotinia rot in Hami melon?
When the disease occurs at the seedling stage, it starts at the base. The diseased part is initially water-soaked and light brown; under high humidity, white cottony mold (that is, mycelium) grows out, taking on a soft rot appearance, and after drying it turns grayish white. The diseased part constricts, and the seedling withers and dies.
When plants are infected at the adult stage, leaf infection starts at the leaf margins, initially appearing water-soaked and pale green; under high humidity, a small amount of white mold grows out, and the lesions turn grayish brown, spreading rapidly and causing the diseased leaves to wither and die. Stem infection mostly enters through the base of the petiole; the lesions are grayish white and slightly sunken, and in the later stage the epidermis splits longitudinally, the pith of the stem is destroyed and becomes hollow, and sclerotia commonly form on the stem surface. Peeling open the stem reveals large numbers of sclerotia, and in severe cases the plant withers and dies.
When the fruit is infected, oily-looking patches usually form first at the stem end, then turn dark green, round and sunken, and gradually expand; the diseased part is covered with large amounts of cottony mycelium and is accompanied by irregular black sclerotial grains.
II. What are the control methods for Sclerotinia rot in Hami melon?
1. Apply fully decomposed organic fertilizer, and after deep plowing, close the greenhouse for high-temperature treatment. Make the maximum temperature inside the greenhouse reach above 60°C to kill the sclerotia in the organic fertilizer and soil. Deep plowing can bury the sclerotia into the lower half of the plow layer, preventing the sclerotia from germinating.
2. Before sowing, float the seeds in 10% salt water 2 to 3 times to remove sclerotia, or use ultraviolet plastic film in plastic greenhouses, which can inhibit the formation of apothecia and ascospores. High ridges covered with plastic film can also be used to inhibit apothecia from emerging from the soil and releasing ascospores, thereby reducing the source of inoculum.
3. Cultivate disease-free seedlings and cover with plastic film after planting to prevent the spread of this disease through seedling raising. Plastic film can be used to inhibit sclerotial germination and the emergence of apothecia.
4. Strengthen the regulation of temperature and humidity in the greenhouse to reduce humidity and raise temperature, thereby reducing the spread of sclerotia and ascospores. In the morning, focus on closing the greenhouse to raise the temperature; in the afternoon, ventilate promptly to remove moisture. After the disease occurs, the night temperature can be appropriately raised to reduce condensation. In early spring, keep the daily average temperature at a high level of 29°C or 31°C; when the relative humidity is below 65%, disease occurrence can be reduced. Prevent excessive watering; when soil moisture is high, appropriately extend the watering interval.
5. Use smoke agents and dust formulations for control. In the early stage of the disease, use 250~300 g of 10% procymidone smoke agent per 667 sq m, fumigate in the evening and then keep the greenhouse closed for 1 night; alternatively, in the evening spray 1 kg of 5% chlorothalonil dust per 667 sq m, applying once every 7~8 days.
6. Spray chemicals. At full bloom or in the early stage of the disease, spray 50% vinclozolin or procymidone wettable powder at 1000~1500 times dilution, or 40% dimethachlon at 1000~1500 times dilution; 50% carbendazim wettable powder or 50% thiophanate at 500 times dilution, spraying once every 5~7 days, for 3~5 consecutive applications.