What are the symptoms of burdock leaf spot? Detailed control methods
Burdock, scientific name Arctium lappa L., also known as yechatou, shuniancao, and laomuzhu erduo. It is a perennial herbaceous plant of the Asteraceae family. The fruit is used as medicine. The root can also be used as medicine. It has the effects of dispersing wind-heat, diffusing the lungs and promoting eruption, and dissipating nodules and detoxifying. It is cultivated throughout the country.
Symptoms Burdock leaf spot mostly occurs in autumn, and seedlings suffer severe damage. It mainly damages leaves and petioles. When seedlings are infected, brown to tea-brown round spots first appear on the leaves, 2—20mm in size, with a smooth surface; later the center of the spot becomes thin and fades to light brown to gray, easily cracking or perforating, with small black dots scattered on it, namely the fungal pycnidia. In severe cases, multiple spots merge into irregular shapes.
Pathogen Phyllosticta lappae Sacc., called burdock phyllosticta, belongs to the Deuteromycotina fungi. Pycnidia are light yellowish-brown, spherical to flat-spherical, 75—1385μm in size, embedded in the tissue, with an ostiole at the top; conidia are colorless and single-celled, elliptical to long elliptical, with rounded ends, 5.5—6.1×4—5 (μm), mostly with 1 septum.
Transmission routes and disease conditions The pathogen overwinters on diseased leaves as pycnidia, and the following year produces conidia that spread through wind and rain, causing primary infection and reinfection. At temperatures of 25—27℃, the disease occurs easily after rain, and the spots become perforated due to rainfall.
Control methods
(1) After harvest, promptly remove diseased residues and bury them deeply or burn them in a centralized manner.
(2) Before sowing burdock, soak the seeds in warm water at 40—50℃ for 3 hours, float off the shriveled seeds, then wrap them in moist gauze and place them at 25℃ to promote germination. Sow when the seed germination rate is above 85%, so that the seedlings grow vigorously and infection at the seedling stage is reduced.
(3) In areas or plots with severe disease, plow deeply in time after autumn to bury the pathogen in the soil.
(4) Carry out crop rotation with other crops for more than 3 years.
(5) Use a suitable planting density to improve ventilation and light conditions in the burdock field.
(6) When disease occurs at the seedling stage, spray 30% Ludebao suspension concentrate at 400 times dilution, or 50% Baijuntong wettable powder at 500 times dilution, 14% copper ammonia complex water agent at 300 times dilution, or 77% Keshade wettable fine powder at 500 times dilution. Apply once about every 10 days, spraying 50—60L of the prepared solution per 667m2. Control 2—3 times. Stop applying the pesticide 3 days before harvest.