Control Methods for Stem Rot in Sweet Potato Cultivation
Sweet potato stem rot, also known as sweet potato wilt, fusarium wilt, stem blight, and so on.
[Pathogen scientific name] Fusarium bulbigenum Cke. et Mass. Var. botatas Wollenw.
[Host crops] Sweet potato and other plants of the Convolvulaceae family.
[Disease diagnosis] The roots of diseased seedlings become swollen and bluish, the vascular bundles turn brown, and the upper part turns yellow and thin. When mature plants are affected, the diseased plants are stunted, the stem base swells, and a bluish halo appears on the surface; when the diseased part is cut open, the vascular bundles can be seen to have turned brown after infection, extending upward from the stem base for 20 to 30 cm. Apart from a few green leaves at the top, all the other leaves of the diseased plant turn yellow, and the older leaves at the lower part successively wither and drop off. In the later stage, the cortex of the diseased part cracks and becomes fibrous, and a pink mold-like growth appears on the surface. When the tuberous roots are affected, the tuber peduncle area becomes rotten; when the upper part of the diseased tuber with discolored vascular bundles is cut crosswise, dark brown ring-shaped spots appear on the cross-section. The pathogen is Fusarium oxysporum f. sp. batatas. The macroconidia are sickle-shaped, with a slightly pointed apical cell and a slightly curved tip on the end cell, and have 3 to 5 septa. The microconidia are single-celled, ovoid to elliptical. The chlamydospores are brown and spherical.
[Occurrence pattern] The pathogen overwinters as mycelium and chlamydospores in diseased tubers or attached to diseased plant residues in the soil. The pathogen can also survive in the soil in a saprophytic state. The pathogen mostly invades through wounds and spreads along the vascular bundles. The cut made when transplanting seedlings is the most important invasion site, and wounds on the roots as well as leaf scars can also be invaded. The pathogen can also invade poorly growing seedlings. The disease can be spread over long distances by diseased tubers and diseased seedlings, and over short distances mainly by soil, flowing water, and farm tools. A soil temperature of 27 to 30°C and high soil moisture favor disease development. Frequent rainfall and large amounts of rain often cause severe outbreaks of the disease.
[Control measures] (1) Select disease-resistant varieties, such as Chaoshanbai, Nanjing 92, Jinshan 247, Taichengshu, Nanruishao, Jinqing No. 9, Xuzhou 18, and so on. (2) Select disease-free seed tubers and use disease-free soil for raising seedlings. (3) Before planting, soak the sweet potato seedlings in 0.2% "401" antibacterial agent for 10 minutes for disinfection. (4) Apply thoroughly decomposed manure. Irrigate moderately, and promptly drain field water after rain. (5) In severely affected plots, carry out crop rotation with grain crops for more than 3 years; rotation with rice for 1 year can already be effective. (6) Promptly pull out diseased plants when found and burn them in a centralized manner or bury them deeply. (7) In the early stage of the disease, promptly spray 30% Luyedan wettable powder at 800 times dilution, or 50% benomyl wettable powder at 1500 times dilution, or 40% Shuangxiaoling aqueous solution at 800 times dilution, or 50% thiophanate-methyl wettable powder at 500 times dilution.