Geranium leaf spot disease is a common disease in spring and summer, and leaf spot disease is most likely to occur in high temperature and rainy season, often causing death and shedding of most susceptible leaves. Stems infected with infestation become black, wilting and rot, and the vascular bundles become brown and black as the basal part is cut open. The damage to the cuttings cannot be rooted, and the stems start to rot and develop upwards, causing the leaves to wilfully die. Symptoms: Geranium leaf spot, including dark brown and brown spot. Melasma: Primary water-stained spots on leaves, semicircular to indeterminate, posteriorly rounded, 2 to 3 mm in diam., with slightly depressed central necrotic spots. Large lesions 6 to 10 mm in diameter. Often limited by veins, it is irregularly shaped, dark brown, with concentric ring veins, and less upper layer of black mold. Spots on the leaf spot scattered or confluent, when severe leaves darken shrinkage and die. The disease is more common in the lower leaves of the plant, but the upper leaves are also vulnerable. Brown spot: The lesion on the leaf is round or oval, 1 to 4 mm in diameter, light brown, grayish to brick red, with a dark brown narrow margin, and the lesions on the underside of the leaf sometimes bulge slightly, and the surface is scattered with dark particles or Dark gray moldy layer. Second, the pathogen and the characteristics of the disease: The above two kinds of leaf spot pathogens are semi-mycotic fungus. Amorphous brown spots are caused by infection with C. sclerotiorum. The near-circular gray spot is caused by infection with Cercospora, Lactobacillus sp., and Trichoderma sp. The above pathogens were initially and re-infected with conidia in the spring and summer through wind and rain. Especially in high temperature and rainy season, it is easy to cause diseases. It is often carried by watering, wind and rain, and splashes of water droplets on the leaves. It is mainly spread through the garden tools such as knives and penetrates from the wound. The environment is humid, and the plants grow too densely and easily. Third, control methods: to create ventilation and light conditions, to avoid excessive density of plants or branches, reduce humidity, prevent shoots leggy. Avoid sprinkler irrigation when watering, in order to prevent water from spreading germs, should be slowly infiltrated along the edge of the basin to prevent excessive watering, water in the basin, causing rot. The diseased leaves must be removed and destroyed in time. Fertilization should not be excessive, excessive nitrogen fertilizer, easily lead to plant growth, no flowering or less flowering. In the early spring or early autumn should be more appropriate application of phosphorus and potassium fertilizers. Spray 50% phenylenede wettable powder 2500 times, or 1:1: 100 Bordeaux mixture before onset. At the beginning of the disease, spray 50% of anthraquinone and 80% of mancozeb (1:1) 1000 times, or 70% of chlorothalonil+70% thiophanate (1:1) 1000 times, and 50% of wet powder 1000. Double fluid, the above-mentioned drugs were alternately sprayed for 3 to 4 times, sprayed once every 7 to 15 days, and secreted before and after sparsely, with good control effect.
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