Identification and control of maize leaf spot

  Corn rot spot (Helminthosporium longicolorum) is a fungal disease. It occurs in Jilin, Liaoning and Hebei provinces, mainly in ears, bracts, leaves and sheaths.

1.Symptoms of Harm
China found that maize leaf spot (Latin name: Bipolaris carbonum Wilson) mainly damaged Ji63 inbred lines. Infection of ear disease from the tip of the ear downwards, the ear grains are coal-stained, and there are black mold layer on the surface and between the grains, that is, conidial pedicels and conidia of pathogenic bacteria. The diseased grains are dry rotten and powdered when twisted by hand. Bract disease is now not plastic stripe blight spot, some dark brown spots, generally do not form a black mold layer, the fungus from the bract leaves to the inner ear, damage the grain and ear axis. Leaf infected with the disease was initially submerged with light green to yellow spots, scattered, and then expanded to round to oval rings. The center of the lesion is light brown with brown margin. The periphery of the lesion is yellow-green halo 5, 5-15 x 3-5 (mm). Sometimes there are long linear patches with black mildew on the surface. When the leaf sheath is infected, the primary brown spots are enlarged to irregular large spots with concentric rings, and the surface produces black mildew. When the inbred line 478 was infected by ear rot, the length of black rot at the ear tip was 5.3-9.3 cm, accounting for 2/5-3/5 of the ear length, while the base of the ear was not infected. The ear symptoms of Ji63 inbred line were similar to those of T race infected with T type sterile line, so attention should be paid to the difference. The symptoms of maize leaf spot on inbred lines 478 and Ji63 are different, which may be different reaction types.

Corn Round Leaf Spot

Corn leaf rot

Symptoms of ear rot of maize leaf spot

2. Morphological characteristics
The conidial pedicels are dark brown, with light top color, solitary or 2-6 clusters, straight or knee-shaped curves, obtuse rounded ends, enlarged basal cells, 3-5 septa, 64.4-99 *7.3-9.9 (um). Conidia are dark olive, long oval, wide in center, narrow at both ends, thick spore wall, blunt round apical cells and basal cells, most of them are straight, small umbilical points, not obvious, with 4-10 septums, mostly 5-7, 33-105 *12-17 (um). The strain has race differentiation.

Cochliobolus carbonum

3. Ways of communication
The transmission route of maize leaf spot is similar to that of maize leaf spot. Because of the severity of panicle disease, the pathogen can overwinter latently on the ear. In the next year, the infectious effect of seed with fungi is very great. Some infected seeds can not germinate and rot in the soil, causing the disease or death of seedlings. In addition, the residual plant residues left on the field or on the stack of straw can also be the initial source of infection in the next year. Under suitable conditions, the spores of overwintering fungi spread to maize plants and incubated for 1-2 days. Conidia were also produced on the lesions, which were transmitted by wind and rain, causing leaf spot or ear rot and repeated reinfection.

4. Pathogenic Conditions
Maize silking to filling stage is the key period for the invasion of the disease.

5.Prevention and control methods
(1) The inbred lines and hybrids with resistance to rot spot are Erhuang, Tiedan 8, Ying 55, Liao 1311, Ji69, Wu 105, Wu 206, Qi 31, Huobai, H84, 017, Jidan 107 and Chundan 34.
(2) It is strictly forbidden to transfer seeds from the affected areas, thoroughly treat the maize residues before emergence, and reduce the source of primary infection.
(3) Spraying 25% Pink Running Wettable Powder 500-600 times or 50% Carbendazim and 70% Manganese Zinc Wettable Powder 400-500 times at the peak of maize silking, i.e. when 50%-80% of ears have silked, once every 7-10 days, twice successively.
(4) For susceptible varieties, seeds can also be mixed with 15% Triazolone wettable powder with 0.3% seed weight before sowing.
(5) For susceptible inbred lines or cultivars, 25% Triazolone (pink rust Ning) wettable powder 1000 times or 40% Fuxing emulsifiable concentrate 8000 times were sprayed at the green tip stage of the ear, once every 10-15 days, and 2-3 times of control.