1. Symptoms The disease mainly damages the leaves and rarely damages the petioles, stems and fruits. Leaf disease, mostly in the melon period, the first disease in the lower leaves, and then the upper part of the leaves. At the initial stage, small gray-brown spots appeared on the leaves, and gradually expanded to light brown or brown spots with unequal round or near-circular edges. The lesions in the middle of the lesions become lighter, sometimes grayish and grayish brown on the edges. When the humidity is high, sparse brownish-yellow mildew is found on the front and back of the lesion, which is the conidiophore and conidia of the pathogen. Severe onset, stems, petioles can also be diseased, lesions oval, gray-brown. When the lesion expands, it can cause the whole plant to die. 2. The pathogen was isolated and cultured by Professor Fang Dechun from Shenyang Agricultural University. It was identified as Corynesporacassiicola (Berk & Curt) Wei. The melon was identified as a fungus of the subphylum Aspergillus. Conidia stems more than solitary, a small number of 3 to 5 clusters, slender, not branched, there are 1 to 7 separated, light brown. Conidiophore apical conidiospores. Conidiophores are clubs or long cylindrical, erect or curved, obtuse at the top, with 5 to 15 septa, conidia pale brown to tan. 3, the incidence of the law 3.1 transmission pathways mainly transmitted by the seed bacteria long distance. The pathogens overwinter in the soil with conidial plexus or mycelia with the diseased body. The bacteria spread through air currents and splashes of rain to carry out initial infestation. The conidiospores generated by the newly infected lesion spread to the surroundings by wind and rain. A growing season of bacteria can be re-infected several times, making the disease increasingly serious. 3.2 Disease conditions The seeds of the bacteria are the main conditions of the disease. Unclean countryside, even planting, small temperature difference between day and night, partial nitrogen fertilizer, the lack of trace elements boron, the incidence is heavier. Humidity in greenhouses, dew condensation on leaves, and lack of light are conducive to the spread and infestation of pathogens. According to the survey, the incidence of breeds bred by a local farmer is heavy and the incidence of other breeds is not high. Temperature 20 ~ 28 °C, leaves a long time of condensation, the incidence is fast. 4. Control measures 1) Select disease-free seed and seed disinfection to select no-ill and disease-free melon seeds. Seeds can be soaked in warm water at 55°C for 15 minutes. 2) Onset fields should be rotated for more than 2 years with non-melon crops. 3) Clear field residues and reduce primary infection sources. 4) Strengthen cultivation management and cultivate disease-free seedlings. Use new soil to raise seedlings, apply sufficient basal fertilizer, timely fertilizer, pay attention to the use of nitrogen, phosphorus and potassium. Use high ridge cover cultivation techniques. Control irrigation, timely release air, reduce indoor humidity, increase lighting, create conditions conducive to the growth and development of cucumber, and is not conducive to the germination and invasion of germs. 5) At the beginning of the disease prevention and treatment, 65% jebumycin (thiomycin) WP 1000 times, or 50% thiram WP 500 times spray control. In severe cases, trace elements boron can be traced.
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