Summer spot, also known as spot blotch in summer, is a serious disease that harms turfgrass. It was first reported in the United States by the United States in 1984. The earliest report in the country was written by Zhao Meiqi et al. (1999). In recent years, lawns have been planted in the area of ​​grassland in the Beijing area. Especially in 1999, the damage was particularly serious, resulting in the death of the whole plant, causing bald patches on the lawn, and seriously affecting the lawn landscape. First, the characteristics of the symptoms: The disease can infect a variety of cool-season valerian, of which the most serious damage to the meadow. Symptoms mainly occur in the high temperature and high humidity season in summer, especially on the mature grassland lawn. The onset turf initially appeared yellow plaques with a diameter of about 3 to 8 cm and gradually expanded thereafter. A typical summer spot is a round withered circle with a diameter of not more than about 40 cm, but it can reach 80 cm at the maximum, and multiple lesions are combined to form a large area of ​​irregular shaped weeds. On a golf course mixed with bentgrass and bluegrass, the diameter of the ring is 30 centimeters. The roots, roots and rhizomes of typical diseased plants were dark brown, and the vascular bundles became brown at the later stage. The outer layer was rotten and the whole plant died. When examined under a microscope, dark brown, verrucose, exophytic hyphae growing parallel to the roots can be seen, sometimes with dark brown irregular aggregate structures. Second, the pathogen: The disease is caused by a fungal disease, scientific name Magnaporthe poae is Ascomycota sub-door. Sexual reproduction forms ascospore shells, which are generally observable only under laboratory culture conditions. They are black, spherical, and have a cylindrical neck. Asexual reproduction forms conidia. Third, the occurrence characteristics: Mainly occurs in the summer high temperature season, when the summer continued high temperature (daytime high temperature of 28 °C to 35 °C, night temperature exceeds 20 °C), the disease will quickly occur. According to field observations, when the temperature of 5 cm soil layer reached 18.3 °C, the bacteria began to infect, at this time only the outer cortical cells infecting the root. Later, with the appearance of hot and rainy weather, a large amount of rainfall or heavy rain after a period of time encountered high-temperature weather, the disease began to apparently apparent and quickly spread and spread, resulting in bald patches of varying sizes on the lawn. The phenomenon of continuous enlargement of the lesion can continue until early autumn. Since bald grass cannot recover within the bald spot, bald spot is still evident during the next growing season. The disease can also be spread through the removal of plant debris and turf transplants. In addition, there are serious cases of hot and humid years and poor drainage and compact areas. The use of arsenate herbicides, available nitrogen fertilizers, and certain fungicides can accelerate symptom performance. Low pruning, frequent shallow irrigation, etc. will aggravate the occurrence of diseases. Fourth, control methods: 1, because the summer spot is a root disease, so any can promote root growth measures can reduce the incidence of disease. Avoid low trimming (usually no less than 5 cm to 6 cm), especially during high temperatures. Slow-release nitrogen fertilizers such as urea or ammonium sulfate containing sulphur coatings are preferred. For deep irrigation, reduce the number of irrigations as much as possible. Perforating, digging grass, ventilation, improving drainage conditions, and reducing soil compaction are all conducive to disease control. 2. Select disease-resistant cultivars (cultivars) or mixed cultivars with disease-resistant cultivars (cultivars). Transforming the diseased area is one of the most effective and economical methods for preventing and controlling summer spot blight. The resistance of different grass species was as follows: perennial ryegrass> tall fescue> åŒåŒ bentgrass> hard fescue> bluegrass. 3. When sowing, use 0.2% to 0.3% of grass disease Ling 2, No. 4 grass disease, or 0.2% of grass disease Ling 3 or thiophanate-methyl and other agents, 500 times to 1000 after landing Herbs such as Baicaoling No.2, Caoxueling No.4 or 1000-fold to 3000-times Caozhiling No.3, 500-800 times thiophanate-methyl, mancozeb, etc Can achieve better control effect. It is usually controlled 2 to 4 times during the disease occurrence period. The critical period of prevention and control is in the late spring and early summer when the soil temperature is between 18°C ​​and 20°C.
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