Symptoms and control methods of cotton boll Aspergillus rot

Symptoms It occurs in all cotton regions. It mainly damages cotton bolls. Initially, water-soaked yellowish-brown spots appear at cracks, insect holes, wounds or splits on the cotton boll, followed by yellow-green or yellowish-brown powdery material that fills the boll cracks, causing the cotton boll to fail to open normally. During continuous rainy weather or high humidity, yellowish-brown or yellow-green fuzzy mold grows, namely the pathogen's conidiophores and conidia, and the cotton lint quality is contaminated to varying degrees or becomes dry-rotted and deteriorated.

Pathogen Aspergillus flavus Link, called yellow aspergillus, Aspergillus fumigatus Fres., called smoke aspergillus, Aspergillus niger van Tiegh., called black aspergillus, all belong to the Deuteromycotina fungi. Aspergillus flavus conidial heads are subspherical, bearing sterigmata in 1-2 layers; the conidiophore vesicle is spherical; conidia are rough, round and yellow, 3.5-5 μm in size; colony color is initially yellow, later becoming yellow-green to brown-green. Aspergillus fumigatus conidial heads are cylindrical, 40 μm in diameter; conidiophores are smooth, greenish, 2-8 μm in diameter; conidia are spherical, rough, 2.5-3 μm in size. Aspergillus niger conidial heads are gray-black to black, round, radiate, 0.3-1 mm in size; conidiophores are 20-40 x 7-10 (μm) in size; the vesicle is spherical to nearly spherical, bearing two layers of sterigmata; conidia are spherical, initially smooth, later becoming rough or bearing fine spines, with colored material deposited in rings or warts, 2.4-4 μm in size, sometimes producing sclerotia.

Transmission routes and disease conditions The pathogen survives the winter as mycelium on diseased residues in the soil. In the following spring, conidia are produced and spread by airflow, invading directly from wounds or by penetrating the epidermis. Aspergillus damage to cotton bolls can invade seeds, causing seed-borne infection, which becomes an important primary infection source of the disease. The conidia of the fungus living saprophytically on cotton bolls spread and multiply via wind and rain, continuing to infect cotton bolls with wounds and splits, causing the disease to expand continuously. The seed-borne and diseased residues of the same year provide inoculum for the disease in the following year, resulting in cyclic infection. This disease is a high-temperature type disease. It is a secondary disease of boll rot. The optimum growth temperature for Aspergillus is 33°C. In the Shanghai cotton region, Aspergillus rot enters its peak damage period from mid-to-late August to early September, and the disease is more severe in years with high temperatures.

Control methods (1) Strengthen cotton field management, pay attention to rational close planting to ensure good ventilation; adopt formula fertilization technology, rationally apply organic fertilizer, with the N:P:K ratio generally suitable at 1:0.4:0.8, avoiding single or excessive application of nitrogen fertilizer; irrigate rationally, strictly prohibit flood irrigation, drain promptly after rain, and prevent moisture retention. Pruning and topping should be timely; remove dead branches, rotten leaves or rotten bolls from the cotton field, concentrate them for deep burial or burning, and reduce inoculum sources. (2) Timely control late-season pests such as cotton bollworm, cotton field corn borer, and diamond bollworm, and do everything possible to reduce wounds. (3) Promptly remove diseased bolls when found, and quickly dry or sun-dry them until they split, increasing lint cotton yield. (4) In the early stage of disease, spray 50% benomyl wettable powder 1500 times solution or 50% iprodione wettable powder 2000 times solution, 70% mancozeb wettable powder 400-500 times solution, 36% thiophanate-methyl suspension concentrate 600 times solution.