Key Technical Points for Pest and Disease Control in the Medicinal Herb Corydalis yanhusuo

Downy mildew: A devastating disease of Corydalis yanhusuo. It begins in early March, with the leaves affected first. Irregular brown lesions appear initially, with indistinct edges. When humidity is high, a layer of white downy mold appears on the underside of diseased leaves, and eventually the leaves rot or dry up.

Control methods: Crop rotation is encouraged. Due to limited land resources in production areas, fully implementing annual rotation is difficult, so in practice plots with rice as the previous crop can be selected to reduce downy mildew damage. Before planting, soak the seed in 40% fosetyl-Al 300-fold solution for 10 min, or in 70% thiophanate-methyl 500-fold solution or 40% carbendazim 500-fold solution for 4 h. At harvest, promptly remove dead branches and fallen leaves from the field to reduce pathogen infection. In early March, as temperatures rise, apply the first spray with 40% fosetyl-Al 250-fold solution or compound rhubarb mixture 500-fold; the second in late March, the third in early April, and the fourth in late April.

Corydalis yanhusuo downy mildew 1. Diseased plant, early stage 2. Enlarged view of diseased leaf 3. Diseased plant, late stage 4. Pathogen (sporangiophores and sporangia)

Corydalis yanhusuo rust: Round to irregular green lesions appear on the leaf surface, slightly sunken, while lesions on the underside of the leaf are raised, producing orange-yellow raised uredinia (summer spore pustules). After the uredinia rupture, the large amount of rust-yellow powder released is the urediniospores, which continuously spread and cause reinfection. Lesions often appear at the leaf tip or margin, and the leaf margin becomes locally curled. The lesions turn brown and eventually perforate. In severe cases, the entire leaf can die. Both petioles and stems can be affected.

Control methods: Strengthen field management, clear drainage ditches, and reduce field humidity; increase application of phosphorus and potassium fertilizers to improve plant disease resistance; at the early stage of disease, spray 95% fenaminosulf 400-500 fold solution, 0.2 degree Baume lime sulfur mixture, or 65% zineb wettable powder 500-fold solution. Starting in early March, spray once every 7 days, alternating chemicals, for 2-3 consecutive sprays.

Corydalis yanhusuo rust 1. Diseased plant 2. Diseased leaf, petiole method 3. Pathogen urediniospores

Sclerotinia rot: It begins in mid-March and is most severe in April. It first affects the stem base near the soil surface. When humidity is high, the stem base rots, plants lodge, and in severe cases patches of plants die. The soil surface becomes covered with white cottony mycelium and irregular black sclerotia of varying sizes resembling mouse droppings.

Control methods: Crop rotation is encouraged, or plots with rice as the previous crop can be selected to reduce sclerotinia rot damage; sclerotinia rot is a relatively stubborn disease. At the early stage of disease, spray with 50% carbendazim wettable powder 800-fold solution, 65% zineb wettable powder 800-fold solution, or 1:1:200 Bordeaux mixture, spraying once every 7-10 d, for 3-4 consecutive sprays.

Pests

The main pests damaging Corydalis yanhusuo include cutworms and white grubs, but damage is generally light in most years and usually no treatment is necessary.