The Harm and Control Methods of Angelica Leaf Spot Disease
The pathogen of Angelica leaf spot disease (Septoria SP.) is a fungus of the genus Septoria in the subphylum Deuteromycotina. The pycnidia are round, and the conidia are filiform to needle-shaped, colorless and transparent, straight or slightly curved, mostly with slightly pointed tips, with 1-3 septa.
1. Harmful symptoms: it damages the leaves. In the early stage of the disease, brown spots appear on the leaf surface, and the lesions gradually expand, with a chlorotic halo appearing around them, the edges appearing reddish-brown, and the center grayish-white. In the later stage, small black particles appear within the lesions. When the disease is severe, most of the leaf becomes reddish-brown, and finally gradually withers and dies.
2. Disease occurrence pattern: the conidia cannot tolerate low temperatures, and germinate easily when exposed to moisture. Because they lack a suitable host, they die, so they are not the main overwintering source of the pathogen. The pathogen mainly overwinters in diseased residual tissues as pycnidia. When the temperature is suitable the following year, the pycnidia produce conidia, which spread through wind and rain and expand the damage. When the spores land on Angelica leaves, they germinate in dew drops or water, produce germ tubes, invade through stomata, and spread and proliferate in the intercellular spaces of the leaf cells, causing lesions to form on the leaves and producing conidia for reinfection. The disease begins in late May, is more severe from July to August, and continues until October. High temperature and high humidity favor the onset of the disease.
3. Control measures: ① In winter, do a good job of cleaning the garden, thoroughly burn the diseased residual tissues, and reduce the source of the pathogen. ② In the early stage of the disease, promptly remove diseased leaves, and spray 1:1:150 Bordeaux mixture or 500 times 65% zineb or 800-1000 times 50% thiophanate-methyl for control, spraying once every about 10 days for 3-4 consecutive times. ③ Establish disease-free seed fields and select disease-free seeds for retention. During the growth period of Angelica, carry out timely intertillage and weeding, and prevent water accumulation in the field during the rainy season to reduce damage losses.