Identification and Control Methods for Major Diseases of Isatis Root

Isatis RootIs the dried root and leaf of Isatis indigotica, a plant of the Brassicaceae family, used as medicine, with the effects of clearing heat, detoxifying, and cooling the blood. During cultivation, there are many diseases, and the common ones are as follows:

I. Isatis Root Downy Mildew

1. Symptoms The leaves at the lower part of the plant near the ground are affected first, then gradually spread to the upper leaves. In the early stage of the disease, only a gray-white downy mold appears on the underside of the leaves, with no obvious spots on the upper surface. The affected parts become uneven, and with further development, they form small chlorotic round spots, which later become brown necrotic spots. In severe cases, the brown necrotic spots merge into large patches, and the edges of the diseased leaves also turn brown and dry up, until the entire leaf dries out and dies.

2. Control measures ① Remove diseased and dead leaves at harvest and dispose of them centrally to reduce overwintering sources of infection. ② Pay attention to drainage and ventilation with light penetration, maintain reasonable close planting, and reduce humidity. ③ Spray pesticides in the early stage of the disease to control it at the initial stage and prevent it from spreading. A 1:1:100-150 Bordeaux mixture, or 65% zineb 500 times dilution, or 25% metalaxyl wettable powder 1000 times dilution can be sprayed once. When spraying, pay attention to spraying the underside of the leaves.

II. Isatis Root Gray Leaf Spot

1. Symptoms Small spots appear on diseased leaves, 2-6 mm in diameter, gray-white in the center, brown at the edges, with thin spots that are prone to perforation. In the late stage of the disease, the spots continue to expand until the entire leaf turns yellow and dies. When humid, a mold layer appears on the upper surface of the leaves.

2. Control measures Same as for downy mildew.

III. Isatis Root Root Rot

1. Symptoms When the roots are affected, the fibrous roots and root tips of the main root are affected first, turning dark brown, until the vascular bundles of the root system show brown lesions. In the later stage, the entire root rots, the aboveground plant wilts, and gradually dies.

2. Control measures ① Crop rotation. ② Choose well-drained sandy loam soil for planting. ③ In the early stage of the disease, irrigate with 1000 times dilution of 50% carbendazim or thiophanate-methyl.

IV. Isatis Root Sclerotinia Rot

1. Symptoms Roots, stems, leaves, and pods are all affected. When leaves are affected, water-soaked greenish-brown spots appear initially, and later the entire leaf rots, leaving only the veins. When stems are affected, the cortex rots, the stems split into a tangled mass, covered with mycelium, and black mouse-dropping-like sclerotia are present inside and outside the stems and on the leaves, with the most sclerotia near the soil surface at the base of the stem. In the later stage, the whole plant wilts, turns yellow, and dies.

2. Control measures ① Paddy-upland rotation. Sclerotia rot after being soaked in water for one month, so paddy-upland rotation can effectively reduce the pathogen. ② During the rainy season, pay attention to field drainage, reduce humidity, maintain reasonable close planting, and ensure ventilation and light penetration. ③ In the early stage of the disease, spray 600 times dilution of 65% zineb.