Methods and Technical Key Points for the Prevention and Control of Licorice Pests and Diseases

The main diseases of licorice are rust, powdery mildew and brown spot.

Licorice rust mainly damages the leaves and tender stems of the plant; the back of infected leaves produces yellow-brown blister-like lesions on one side, and after the epidermis ruptures, brown powder is released.

Prevention and control method: burn the leaves of diseased plants. In the early stage of the disease, treat with a 1000-fold dilution of Fenxiuning; you can also use 0.3 degrees Baume lime sulfur mixture, or a 500-fold dilution of 65% wettable zineb, or a 200-fold dilution of dithianon sodium for spray control, spraying once every 7 to 10 days, and 2 to 3 consecutive sprays are sufficient.

Licorice brown spot is also called leaf spot; it mainly damages the leaves, producing round or irregular lesions on the leaves, with the center of the lesion gray-brown and the edges brown, and black mold-like material on both sides of the lesion.

Prevention and control method: in the early stage of the disease, use the broad-spectrum antibacterial pesticide Nongkang 120 (Gaizhiling) at a 1200-fold to 1500-fold dilution, spraying once every 7 to 10 days, for 2 to 3 consecutive sprays. Or spray Bordeaux mixture at 1:1:100 to 1:1:160, or spray a 1500-fold to 2000-fold dilution of 70% thiophanate-methyl wettable powder.

The main licorice pests include underground pests such as licorice scale insects and white grubs; aboveground pests such as alfalfa plant bugs, short-haired weevils and aphids; and seed pests such as licorice bean weevils and licorice seed leafhoppers.

The short-haired weevil has its peak damage period from July to early August, mainly feeding on licorice leaves. Prevention and control method: use as little or no pesticide as possible; biological pesticides and low-toxicity pesticides can be selected, such as 2.5% deltamethrin emulsion at 1000, 2500 or 5000-fold dilutions, applying 45 kg of spray solution per mu. When the insect population density reaches 100 per hundred plants, chemical control may be considered, but the future impact on licorice quality must be taken into account.

If aphids occur, spray a 1000-fold to 2000-fold dilution of 50% fenitrothion or a 1500-fold to 2000-fold dilution of 40% dimethoate emulsifiable concentrate. A 1500-fold dilution of 80% dichlorvos emulsifiable concentrate can also kill aphids. Once every 7 to 10 days, several consecutive applications are sufficient to eliminate them.