Symptoms The lesions occur on both sides of the leaf. The lesions are round, nearly circular to irregular, 1–8 mm wide, light brown to brown, grayish-white in the center, yellow-brown on the edges, and slightly pale lesions on the back of the leaves. .
The pathogen Cercosporalactucae-sativaeSawada called C. oleracea belongs to the genus Fungi (asexual spores). Conidiophores and conidia are born on both sides of the leaf, with no pedestal or only a few brown cells. Conidiophores solitary or 1-12 clustered, light brown, not branched, with 1 to 4 geniculate knees, conical at the top, 0 to 4 septa, 25 to 1154 to 6 (μm). Sclerotium was markedly thickened and was 2 to 3 μm wide. Conidia needle-shaped to cylindrical, colorless, erect, top apex, base inverted conic, multiple septa, 31 ~ 117.53 ~ 5 (μm), in addition to harm lettuce, but also harm mountain buckwheat, mountain lettuce, long Lettuce, leaf bitter leeks.
The disease transmission route and onset conditions were overwintering on mycelia and conidia plexus on the diseased body, initial infection and reinfestation with conidia, spread by airflow and rain splash. Normally, it is favorable for the incidence of rainy or foggy, dew-opening weather, poor plant growth, or excessive application of nitrogen fertilizer, which will increase the incidence.
Prevention methods (1) Pay attention to field health, combine the picking disease leaves to collect diseased residues and carry them out to burn out. (2) Drainage pits, application of organic fertilizer to avoid partial nitrogen fertilizer application, timely spraying large natural algae, etc., so that plants grow robustly and enhance resistance. (3) Spraying 78% of MnZn WP 500 times or 2.5% of fludioxonil suspension 1200 times, 50% of iprodione WP 1500 times, 86.2% of cuprous oxide wettable powder 1000 times liquid, every 10 to 15 days 1 time, continuous control 2 to 3 times.
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