What are the control methods for southern blight in jasmine?
Jasmine southern blight is the most serious disease of jasmine. When the disease is severe, it causes the plants to wither and die, greatly affecting yield.
[Distribution] Suzhou, Hangzhou, Shanghai, Nanjing, Fuzhou, Taiwan, China.
[Symptoms] The disease occurs at the root crown and roots, and under suitable conditions can spread to the lower leaves. The root crown area turns brown and rots, gradually spreading and expanding, producing a white silky film, mostly radiating outward, especially noticeable at the edges. The silky mycelium can spread to the soil near the root crown, and in severe cases the entire pot of soil is filled with white mycelium. Later, sclerotia form on the mycelial film. The sclerotia are initially white, gradually deepening to yellow, tea-brown and finally dark brown, about the size of a rapeseed. After the cortex rots and dies, the leaves wither and drop, and in severe cases the whole plant dies. Under very humid conditions, the mycelium can directly spread to the lower leaves, producing large amounts of white silky film that envelops the lower branches and leaves, causing water-soaked spots on the leaves and producing mycelium on the silky film.
[Pathogen] The pathogen is a fungus, Sclerotium rolfsii. It belongs to Deuteromycotina, Hyphomycetes, Agonomycetales, genus Sclerotium. The sclerotia are initially white, then gradually change from pale yellow to chestnut-brown to tea-brown, with a smooth surface, spherical or nearly spherical, 0.8-2.3 mm in diameter, very similar to rapeseed. The optimum temperature for the pathogen's development is 32-33°C, with a maximum of 40°C and a minimum of 8°C. Its pH tolerance range is pH 5-9.
[Disease pattern] The pathogen has a wide host range, reaching more than 200 species. It overwinters as sclerotia or mycelium in soil, diseased plant residues and weeds. Sclerotia can survive in soil for more than 4 years, but their survival period is very short under high humidity conditions, and they are not tolerant of water immersion. The pathogen spreads through the soil as mycelium, and long-distance transmission relies on flowing water or the human movement of diseased seedlings, diseased soil and diseased pots. When using garbage soil or vegetable garden soil for repotting, the disease is likely to occur; continuous cropping or repeated use of diseased potting soil makes the disease severe; high humidity makes the disease likely to occur.
[Control methods]
(1) Horticultural control: rotation, centralized treatment of diseased potting soil, preferably by dumping it into rice paddies; potting soil should be taken from disease-free plots, preferably paddy field soil. Organic fertilizer must be fully decomposed; propagation material should be cut from disease-free plants; avoid dense stacking during overwintering in the greenhouse.
(2) Remove diseased plants and disinfect the soil. When diseased plants are found early, they should be promptly pulled up and burned or deeply buried, and the diseased holes should be watered with 86.2% Copper Master at 800-1200 times dilution, 50% amobam at 500 times dilution, or sprinkled with lime powder. The removal of diseased plants should be carried out before sclerotia form.
(3) Chemical control: 50% Tuzet at 1000 g per 666.6 sq m; in the early stage of disease, drench with 50% amobam at 1000 times dilution, and apply again after 7-10 days to kill the pathogen in the soil. Apply 70% thiophanate-methyl at 1000 times dilution or 50% carbendazim at 1000 times dilution to the soil around the base of the plant stems to inhibit the spread of the disease. Then water with other fungicides; for potting soil, 82 Trichoderma bran preparation (product of the Department of Plant Protection, Zhejiang Agricultural University) can be used, mixed into the soil at 0.5% of the soil weight, and used after potting; part of the potting soil can also be removed and replaced with soil mixed with the preparation.
(4) Physical control: sterilize the potting soil by heating.
(5) Biological control. Using the antagonistic fungus Trichoderma harzianum to control jasmine southern blight has good results. First culture the Trichoderma strain, then mix it onto sterilized bran to prepare a Trichoderma preparation. When using the Trichoderma preparation, mix it evenly with fine soil and apply it to the soil. The soil should maintain a certain humidity to promote the mass growth and reproduction of Trichoderma in the soil, thereby inhibiting the growth of the southern blight pathogen and achieving disease control.
(6) Rational fertilization. Applying undecomposed organic fertilizer to the soil surface will aggravate the occurrence of southern blight, so organic fertilizers (such as manure) should be used as base fertilizer and buried deep in the lower soil layer. If used as a top dressing, it must be fully decomposed before application.