Corn leaf spot!

Ears, bracts, leaves and leaf sheaths are damaged. The disease mainly harms Ji 63 inbred lines in China. The infected ear infects downward from the ear tip, the ear grains are polluted by coal, and there is a layer of black mold on the surface and between grains, that is, the conidiophore and conidia of the pathogen. The diseased granules are dry and rotten, and they are twisted into powder by hand. When the bract leaves are infected, there are no plastic spots, some spots are dark brown, and generally no black mold layer is formed. The pathogen extends from the bract leaf to the ear, which is harmful to the grain and ear axis. The infected leaves are scattered with small pale green to yellow spots soaked in water, and then expand into round to oval wheel spots. The focus is light brown in the middle and brown in the edge, with yellow-green halo around it, with the size of 5- 15× 3-5 (mm). Sometimes long linear spots will be formed, and a black mold layer will also be formed on the surface of the spots. When the leaf sheath is infected, brown spots appear at first, and then expand into irregular large spots, and there are also concentric rings, and a black mold layer is produced on the surface. When the ear rot of leaf spot infected inbred line 478, the length of ear tip black rot was 5.3-9.3 cm, accounting for 2/5-3/5 of the ear length, but the ear base was not infected. The ear symptoms of Ji 63 inbred line are similar to those of T-type sterile line infected with maize leaf spot T race, so attention should be paid to the difference. Inbred line 478 and Ji 63 have different symptoms, which may be different reaction types. Distributed in Jilin, Liaoning, Hebei and other provinces.

The pathogenic Penicillium carbonum Wilson is called Helminthosporium carbonicum, belonging to Hemiptera subfamily. Different names B. Zeicola (Stout. )Shoem。 Myxomycetes carbonisatus The sexual state is Cochliobolus carbonum Nelson, the conidia leaves are dark brown, the top is light, solitary or 2-6 clusters, erect or knee-shaped, the end is round, the basal cells are enlarged, and there are 3-5 septa with the size of 64.4-99×7.3-9.9(μm). Conidia are dark olive in color, rectangular in shape, wide in center, gradually narrowed at both ends, thick in spore wall, blunt in apical cell and basal cell, mostly erect, small in umbilicus, inconspicuous, with 4- 10 septa, mostly 5-7, with a size of 33-105×12. The strain has physiological race differentiation.

Transmission route and onset conditions The transmission route of the disease is similar to that of the big and small spot disease. Because of the serious lesions in the ear, bacteria can hibernate in the ear. In the next year, the seeds with bacteria played a great role in spreading diseases. Some infected seeds could not germinate and rotted in the soil, resulting in illness or death of seedlings. In addition, the residues of diseased plants left in the fields or straw piles can also become the primary source of infection in the following year. When the conditions are suitable, the spores of overwintering pathogen spread to maize plants, and germinated and invaded after L-2 days of incubation. Conidia are produced on the diseased spots, which are spread by wind and rain, causing leaf spot or ear rot and reinfecting many times. The key period of maize invasion is from silking to filling.

Selection of resistant varieties for control methods (1) At present, the inbred lines and hybrids resistant to circular leaf spot in production are Tiedan No.8, Ying 55, Liao131,Ji 69, Wu 105, Wu 206, Qi 3l and so on. (2) It is forbidden to adjust the seeds from the epidemic area, and thoroughly treat the diseased residues before the emergence of corn to reduce the primary infection source. (3) At the peak of corn silking, that is, when 50%-80% of ears have spun silk, spray 500-600 times of 25% triadimefon wettable powder or 400-500 times of 50% carbendazim and 70% mancozeb wettable powder 7- 10 every 7-/0 days. (3) For susceptible varieties, seeds can also be dressed with 15% triadimefon wettable powder which accounts for 0.3% of the seed weight before sowing. (4) For susceptible inbred lines or varieties, spray 10- 15 days with 25% triadimefon (triadimefon) wettable powder or 8000 times of 40% Fuxing EC 1 time, for a total of 2 times.