Detailed Explanation of the Latest Control Methods for Watermelon Anthracnose
Watermelon anthracnose can occur throughout the entire growing period, but it is most severe during the mid to late stages of plant growth, causing defoliation, plant death, and fruit rot. When seedlings are affected, round brown lesions appear on the cotyledons, and as the disease progresses the base of the young stem turns dark brown and constricts, and may even collapse. When mature plants are affected, water-soaked round pale yellow spots appear on the leaves, later turning brown with purple-brown edges and a pale brown center, with concentric rings. After the lesions expand and merge, they easily cause the leaves to perforate and dry up. On immature fruits, the initial lesions appear as water-soaked, pale green round spots; on mature fruits they begin as raised lesions and later expand into brown depressions, arranged in rings with many small black dots, and in humid conditions a pink sticky substance is produced, with the fruit often becoming deformed or turning black and rotting.
Damage Symptoms of Watermelon Anthracnose
Watermelon anthracnose mainly damages the leaves, but can also damage the stems and vines, petioles, and fruits. When seedlings are affected, round or semicircular brown or dark brown lesions appear on the edges of the cotyledons, often with a dark brown halo around them, and small black dots or pale red sticky material are often scattered on the lesions. When the stem near the ground is affected, its base turns dark brown, constricts and thins, and the seedling collapses. When the vine or petiole is infected, water-soaked yellow-brown oblong spots first appear, slightly sunken, later turning dark brown; after the lesion encircles the stem, the entire plant dies. When leaves are infected, round or irregular water-soaked spots first appear, sometimes with concentric rings, and in dry conditions the lesions easily break apart and perforate. In humid conditions, a pink sticky substance is produced on the lesions. When fruits are infected, water-soaked sunken brown round or oblong spots first appear, often with cracking, and in high humidity a pink sticky substance is produced on the spots.
Occurrence Pattern of Watermelon Anthracnose
Watermelon anthracnose is caused by infection by fungi of the genus Colletotrichum in the subphylum Deuteromycotina. The optimum temperature for its occurrence is 22-27°C; below 10°C and above 30°C the lesions stop growing. The pathogen overwinters in plant debris or in the soil; in the following year, when temperature and humidity are suitable, the overwintering pathogen produces spores and begins primary infection. The pathogen attached to seeds can directly invade the cotyledons and cause seedling disease. Under suitable conditions, the pathogen then produces acervuli or conidia for secondary infection. Conidia are mainly spread through running water, wind and rain, and human production activities. When harvesting melons, if the fruit surface carries conidia, infection can also occur during storage and transport. The occurrence of anthracnose is greatly related to humidity; at suitable temperatures, the higher the relative humidity, the more severe the disease. When relative humidity is 87%-95%, the incubation period of the pathogen is only three days; the lower the humidity, the longer the incubation period, and when relative humidity drops below 54%, the disease does not occur. In addition, excessive use of nitrogen fertilizer, poor drainage, poor ventilation, excessive density, weak plants, and continuous cropping can lead to severe disease.
Preventive Measures for Watermelon Anthracnose
During the period when the disease commonly occurs, spray "Sujing" 30ml diluted in 15kg of water, once every 5—7 days.
Agricultural Control of Watermelon Anthracnose
For the control of watermelon anthracnose, emphasis should be placed on selecting disease-resistant varieties, regulating indoor humidity to reduce it below 70%, and carrying out protection throughout the entire growth period.
1. Select disease-resistant varieties: choose Qihong, Qilu, Kaiza No. 2, Kaiza No. 5, Jingxin, and Xingmi.
2. Disinfect seeds and cultivate disease-free strong seedlings.
3. Implement crop rotation, apply fertilizer reasonably, reduce the amount of nitrogen chemical fertilizer, and increase the application of potassium fertilizer and organic fertilizer.
4. Fully cover the ground with plastic film and strengthen ventilation and air regulation to reduce indoor air humidity below 70%.
5. Plant at a reasonable density and prune scientifically to prevent excessive density and reduce the microclimate humidity indoors.
6. Use bactericidal pesticides scientifically.
Treatment Methods for Watermelon Anthracnose
1. Spray "Sujing" 50ml + "Garlic Oil" 15-20ml diluted in 15kg of water, once every 3—5 days, for 2-3 consecutive applications; after the disease is under control, switch to the preventive program.
2. In protected and open fields, at the early stage of disease, spray 50% thiophanate-methyl wettable powder at 800 times dilution plus 56% azoxystrobin chlorothalonil at 800 times dilution, or mix and spray 50% carbendazim wettable powder at 800 times dilution plus 75% chlorothalonil wettable powder at 800 times dilution.
3. In addition, you may also choose 38% oxadixyl, pyrimethanil and copper and kresoxim-methyl at 800 times dilution, 36% thiophanate-methyl suspension concentrate at 500 times dilution, 80% anthracnose thiram wettable powder at 800 times dilution, 2% antimycin (pyrimidine nucleoside antibiotic) aqueous solution at 200 times dilution, or 2% wuyiencin aqueous solution at 150 times dilution, once every 7~10 days, for 2~3 consecutive treatments.
4. Or 20% flusilazole and prochloraz at 1000 times dilution, 80% anthracnose thiram at 800 times dilution, or 25% difenoconazole water-dispersible granules at 1000 times dilution. Spray once every 7 days, for 3-4 consecutive sprays, alternating the chemicals in turn, for a better control effect.
5. 20% imazalil emulsion in water at 800 times dilution has a special effect on anthracnose.