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Identification and Control Methods of Cotton Seedling Red Rot

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Symptoms This disease occurs in all cotton regions of China, with severe damage in the Yangtze River Basin and Yellow River Basin cotton regions, and it also occurs in the Liao River Basin. It can infect plants at the seedling stage and boll stage. When infected at the seedling stage, the young sprouts are damaged before emergence, and the sprouts become reddish-brown and rot. After emergence, the roots of affected cotton seedlings show yellowing of the root hairs and lateral roots, which later turn blackish-brown and rot. When the young stem is infected, the vascular bundles turn dark brown, yellow streaks appear at the base of the young stem near the ground, and later turn brown and rot. The young roots and young stems swell, and grayish-red irregular spots form on the edges of the cotyledons and true leaves. Under high humidity, a pink mold layer forms on the surface, which is the pathogen

Symptoms This disease occurs in all cotton regions of China, with severe damage in the Yangtze River Basin and Yellow River Basin cotton regions, and it also occurs in the Liao River Basin. It can infect plants at the seedling stage and boll stage. When infected at the seedling stage, the young sprouts are damaged before emergence, and the sprouts become reddish-brown and rot. After emergence, the roots of affected cotton seedlings show yellowing of the root hairs and lateral roots, which later turn blackish-brown and rot. When the young stem is infected, the vascular bundles turn dark brown, yellow streaks appear at the base of the young stem near the ground, and later turn brown and rot. The young roots and young stems swell, and grayish-red irregular spots form on the edges of the cotyledons and true leaves. Under high humidity, a pink mold layer forms on the surface, which is the conidia of the pathogen. In production, cotton fields sown early or experiencing low-temperature and rainy weather, where root rot is severe, suffer from dead seedlings. When the stem base of adult plants is infected, ring-shaped or localized brown lesions form, the cortex corrodes, and the xylem turns yellowish-brown. For boll infection, see Cotton Boll Red Rot.

Pathogen Fusarium moniliforme var. intermedium Neish et Leggett, called intermediate variant of Fusarium moniliforme; F. semitectum Berk. et Rav., called Fusarium semitectum; F. avenaceum (Corda ex Fr.) Sacc., called Fusarium avenaceum; F. graminearum Schwabe, called Fusarium graminearum, and various other fungi, all belonging to the Deuteromycotina fungi. F. moniliforme var. intermedium on PDA medium has velvety colonies, pink, light purple, or rose-colored. It produces conidiogenous cells with both monophialides and polyphialides. Microconidia are single-celled, oval or narrow melon-seed-shaped, borne in chains or false heads, measuring 5.3-10.8 x 2.7 x 4 (μm).

Transmission routes and disease conditions The pathogen overwinters with diseased residues or saprophytically in the soil, and the conidia and mycelium produced by the pathogen become the primary infection source for the following year. At the seedling stage, the primary infection source can also be conidia attached to the short fuzz on seeds and mycelium latent inside the seeds, which invade and damage the young sprouts or seedlings after sowing. This fungus lives saprophytically during the cotton growing season. At the boll stage, conidia or mycelium are spread to cotton bolls by wind, rain, insects, and other vectors, invading through wounds and causing boll rot. Diseased bolls cause the seeds to carry the fungus both internally and externally, forming a new infection cycle. Red rot pathogens grow and are active within a temperature range of 3-37°C, with the optimum at 20-24°C. High humidity is favorable for infection. The incubation period is 3-10 days, and its length varies with environmental conditions. Fewer sunshine hours, greater rainfall, and more rainy days can cause major epidemics. At the seedling stage, low temperature and high humidity lead to more severe disease. At the boll stage, rainy and low-temperature conditions with high humidity also easily cause disease. When cotton plants are excessively vegetative or cotton bolls are damaged by diseases and pests, with many mechanical wounds, the pathogen easily invades and the disease is severe. If the climate is dry during the boll cracking stage, the disease is mild.

Control methods (1) Select healthy, disease-free cotton seeds. (2) Pay attention to cleaning the field, promptly remove diseased plants, and promptly clear away dead branches, fallen leaves, rotten bolls, and other debris from the field, and burn them in a centralized manner to reduce the primary infection sources of the pathogen. (3) Sow at the appropriate time, strengthen seedling-stage management, adopt formula fertilization techniques, promote rapid and robust growth of cotton seedlings, and enhance plant disease resistance. (4) Strengthen cotton field management, promptly control diseases and pests at the boll stage, avoid wounds, and reduce opportunities for pathogen infection. (5) Seed treatment. Mix 1 kg of 50% carbendazim wettable powder per 100 kg of cotton seeds. (6) Boll-stage control. First, combine control with the management of other diseases. Second, promptly spray 1:1:200 Bordeaux mixture or 50% thiophanate-methyl (thiophanate-methyl) wettable powder 800 times solution, or 50% carbendazim wettable powder 1000 times solution, 50% benomyl wettable powder 1500 times solution, or 65% jiameiling wettable powder 1500 times solution, spraying 100-125 L of the prepared solution per 66 sq m, once every 7-10 days, for 2-3 consecutive sprays.

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