Key Points of Pest and Disease Control Techniques for the Chinese Medicinal Herb Isatis Root

Diseases

White rust:Caused by a type of flagellate fungus. Leaves, stems, and flowers can all be affected, with more occurrences on the undersides of leaves. Generally, excessive nitrogen fertilizer, tender plants, abundant rain, high humidity, and alternating cold and warm conditions lead to more severe disease. Continuous cropping results in more sources of infection, making the disease even more severe.

Control methods: (1) Thin seedlings in time, clear ditches for drainage, carry out intertillage and weeding, reduce field humidity, promote robust seedling growth, and enhance disease resistance. (2) During the seedling stage, combine thinning with removal of diseased seedlings; in the later stage, pay attention to removing diseased leaves to prevent the spread of pathogens. (3) At the early stage of disease, spray Bordeaux mixture to inhibit the spread of the disease. (4) At harvest, collect and burn diseased and residual branches to eliminate overwintering sources of infection.

Black spot disease: (1) Symptoms. Circular or nearly circular lesions appear on leaves, brown to dark brown, often with concentric rings, surrounded by a chlorotic halo. The lesions are relatively large, generally 3—l0mm in diameter. On the surface of the lesions there is dark brown mold-like growth, which is the pathogenic fungus's conidia. In the later stage, diseased leaves wither and fall off. (2) Disease pattern. The pathogen overwinters as conidia in diseased tissues and serves as the primary infection source for the following year. It begins to occur from May and can continue until October. Among these months, June—September is the most severe period. Hot and rainy seasons are favorable for the disease.

Control measures: ① Reasonable crop rotation, clean the field, and eliminate overwintering sources of inoculum. ② Strengthen field management, increase application of phosphorus and potassium fertilizers, and improve disease resistance. ③ At the early stage of disease, spray 1:1:100 Bordeaux mixture or 65% zineb 600~800 times solution, spraying once every 10~15d, with 75kg per mu, continuously spraying 2—3 times.

Gray leaf spot: (1) Symptoms. Small circular lesions appear on affected leaf surfaces, slightly sunken. The lesion edges are brown, and the center is grayish white. The lesions become thin and brittle, prone to cracking or perforation. The lesions are 2-mm in diameter, and brown mold-like growth appears on the leaf surface, which is the pathogenic fungus's fruiting body. The disease first occurs on old leaves and spreads from bottom to top. In the later stage, the lesions may merge with each other, and the diseased leaves wither and die. (2) Disease pattern. The pathogen overwinters with diseased residual tissues and becomes the primary infection source for the following year. Seeds can also carry the pathogen. The disease begins in early June, with the peak period from late month to early September. When the average temperature over 6 days is 23°C~25°C, it is favorable for the disease, and it spreads rapidly.

Control measures. ① Crop rotation and cleaning the field to reduce sources of inoculum. ② Open ditches for drainage during the rainy season to reduce field humidity. ③ At the early stage of disease, spray 1:1:100 Bordeaux mixture for protection, or use 65% zineb 600—800 times solution for spray control.

Sclerotinia rot:This is one of the main diseases of Isatis root. When the disease is severe, plants die in large numbers. (1) Symptoms. It affects roots, stems, leaves, and pods, with the stem being the most severely affected. At the early stage of disease, the basal leaves are affected first. The lesions initially appear water-soaked, then turn greenish brown, and finally the leaves rot, leaving only the veins. During rainy and highly humid conditions, the affected stems are filled with white mycelium, the cortex soft-rots, and the stems break apart into a tangled mass. The stems are hollow and bear black mouse-dropping-like sclerotia. Sclerotia can be seen on the stem surface or leaves. After the stems and leaves are affected, the branches and leaves wilt and gradually die. (2) Disease pattern. The pathogen overwinters as sclerotia left in the soil or mixed among seeds, becoming the primary infection source for the following year. During the growing period, ascospores are dispersed by wind and rain for secondary infection, expanding the damage. The disease occurs in mid-April, with the peak period from late April to May. Excessive application of nitrogen fertilizer, poor drainage, extensive management, and water accumulation after rain all favor the disease.

Control measures: ① Paddy-upland rotation, avoiding rotation with cruciferous crops. ② Strengthen field management, promptly dredge ditches and drain water after rain, apply less nitrogen fertilizer, increase phosphorus and potassium fertilizers, and improve plant disease resistance. ③ At the early stage of disease, spray 65% zineb 400—600 times solution, with 75—lOOkg per mu, once every 7d, continuously spraying 2—3 times.

Downy mildew:Caused by a type of flagellate fungus. It mainly damages leaves. It generally begins in early June and becomes severe in mid-July. Diseased residual tissues in the soil are the primary infection site for downy mildew. During the growth period of Isatis root, conidia on the undersides of diseased leaves spread through wind and rain, causing repeated infection.

Control methods: (1) Seed selection: Choose disease-free plots as seed fields, harvest seeds from seed plants separately, and store seed roots separately. (2) Clean the field: When digging Isatis root, remove dead branches and residual leaves above ground to reduce sources of infection. (3) Pay attention to drainage: High soil moisture is a favorable condition for the occurrence of Isatis root downy mildew, so drain water promptly after rain to reduce field humidity. (4) Reasonable crop rotation: Rotate with gramineous crops such as corn. (5) Spray control: At the early stage of disease, spray 50% thiophanate-methyl 800-1000 times solution, or 5% carbendazim 1000 times solution.

Powdery mildew:Caused by a type of ascomycete fungus. It mainly damages leaves. Generally, low temperature and high humidity, excessive nitrogen fertilizer application, overly dense plants, and poor ventilation and light transmission all make the disease more likely to occur. Under high temperature and dry conditions, the disease stops spreading.

Control methods: (1) Remove accumulated water in the field to inhibit disease occurrence. (2) Reasonable close planting, rational combination of nitrogen, phosphorus, and potassium fertilizers, so that plants grow robustly and disease resistance is enhanced. (3) At the early stage of disease, remove diseased leaves; after harvest, remove diseased residual plants and fallen leaves and burn them centrally. (4) Chemical control: Spray 65% ziram wettable powder 300-500 times.

Pests

Cotton bollworm:Damages in August-September. 1st-3rd instar larvae bite and feed on leaf mesophyll, leaving the epidermis and forming transparent small spots; 5th-6th instar larvae bite and feed on entire leaves. Mature larvae spin thin cocoons at leaf edges or between stems and leaves and pupate. In winter, pupae overwinter in field weeds and hatch the following year to cause damage.

Control method: Spray 90% trichlorfon 1500 times solution. When spraying, focus on spraying the middle and lower old leaves for obvious effect.

Aphids:When they occur, they mostly gather densely on tender leaves and new shoots to suck sap, causing leaves and tender shoots to curl and wither, resulting in poor growth.

Control methods: (1) After harvesting Isatis root, remove residual branches, fallen leaves, and weeds at field edges, and burn them centrally to eliminate overwintering pest populations. (2) Chemical control: Spray 4% dimethoate 1500 times solution. Or use homemade pesticide for spraying. Method for making homemade pesticide: 0.5 kg tobacco stems, 0.5 kg lime, and 25 kg water to make tobacco stem lime water solution.

Cabbage white butterfly: Pieridae, cabbage white butterfly, Pieris repe L. Larvae damage leaves. Before the 2nd instar, they only feed on leaf mesophyll; after the 3rd instar, they feed on leaves, forming holes and notches, and green granular feces can be seen.