Cotton boll aspergillosis

Symptoms occur in all cotton areas. It mainly damages cotton bolls. At first, water-soaked yellow-brown spots are produced at the cracks, wormholes, wounds or cracks of cotton bolls, and then yellow-green or yellow-brown powder is produced to fill the gaps of cotton bolls, causing cotton bolls to fail to crack normally. When it rains or humidity is high, yellow-brown or yellow-green villous mold grows, i.e. conidia and conidia of pathogens. The cotton wool quality is polluted to varying degrees or deteriorated by dry rot.

Aspergillus flavus Link, Aspergillus fumigatus Fres., Aspergillus niger Tiegh., belong to subphylum semi-fungi. Aspergillus flavus conidia spike subspherical, 1-2 layers of upper pedicels, conidia apex spherical, conidia rough, round yellow, size 3.5-5μm, colony color yellow at first, then yellow-green to brownish green. Aspergillus fumigatus conidia spikelets cylindrical, 40μm in diameter, conidia smooth, greenish, 2-8μm in diameter; conidia spherical, rough, 2.5-3μm in size. Aspergillus niger conidia spike grayish black to black, round, radial, 0.3-1mm in size; conidia peduncle 20-40×7-10(μm) in size; apical sac spherical to subspherical, with two layers of pedicels on the surface; conidia spherical, initially smooth, then rough or spinulose, colored material deposited into annular or nodular shape, 2.4-4μm in size, sometimes producing sclerotia.

Pathways of transmission and conditions of disease The pathogen survives as mycelium on residues in the soil across the Arctic Ocean. Conidiospores produced in the next spring were transmitted by air flow and invaded directly from wounds or epidermis. Aspergillus damaged cotton bolls and invaded seeds, causing seeds to carry fungi, which became an important initial infection source of the disease. The conidia of the pathogen, which were necrotic on cotton bolls, spread by wind and rain, continued to infect cotton bolls with wounds and cracks, and the disease continued to expand. The seeds and diseased bodies of the same year provided the pathogen source for the disease occurrence in the next year, and the cyclic infection occurred. The disease belongs to high temperature disease. It's a secondary disease of rotten bolls. The optimum temperature for Aspergillus growth is 33℃. Aspergillus disease in Shanghai cotton area is more than in mid-late August to early September, and the disease is serious in high temperature years.

Control methods (1) Strengthen cotton field management, pay attention to reasonable dense planting, and achieve good ventilation; adopt formula fertilization technology, reasonably apply organic fertilizer, and the ratio of nitrogen, phosphorus and potassium is generally 1∶0.4∶0.8, avoiding single application of nitrogen fertilizer; rationally irrigate, prohibit flood irrigation, and drain water in time after rain to prevent moisture retention. Pruning and branch-cutting should be carried out in time to remove dead branches and rotten leaves or rotten bolls of cotton fields, concentrate on deep drought or burn, and reduce bacterial sources. (2)Timely control cotton bollworm, corn borer, diamond and other late pests, do everything possible to reduce wounds. (3)Discovered diseased bolls are removed in time, and the diseased bolls are dried or dried rapidly to increase lint yield. (4)At the early stage of disease, spray 50% benomyl WP 1500 times or 50% prohydantoin WP 2000 times, 70% mancozeb WP 400-500 times, 36% thiophanate-methyl suspension 600 times.