What are the comprehensive pest control methods for licorice?

The leaf beetle (Apophylia flavovirens)

This insect is a leaf-eating pest of the subfamily Galerucinae in the family Chrysomelidae. It causes very serious damage to licorice and is one of the main obstacles to developing licorice production. This insect is distributed to varying degrees in **, the Hexi region of Gansu Province, and the licorice-producing areas of Liaoning Province. It mainly damages sweet licorice (Glycyrrhiza glabra) and does not harm other tree, shrub, or grass plants. Throughout the entire growing season, adult insects cause the primary damage and have a large feeding capacity; adults and larvae often overlap in causing damage.

Control methods: Experiments have shown that dichlorvos emulsion, trichlorfon, phoxim emulsion, and omethoate emulsion all have very good insecticidal effects, and a 1000-fold mixed solution of dichlorvos and trichlorfon sprayed before 11 a.m. gives the best insecticidal effect. In addition, spraying a 1000-fold dilution of dichlorvos emulsion also has an excellent control effect.

Leaf beetles

The main species are the elm leaf beetle (Pyrrhalta maculicollis) and the yellow-spotted leaf beetle (Monolepta hieroglyphica), which are the primary leaf-eating pests of licorice in beach lands such as the Hetao floodplain and lake silt deposits. They are also distributed in other production areas, but the damage is lighter or causes no harm. Both adults and larvae feed on licorice leaves, leaving the leaves riddled with holes after damage. They feed on the leaf mesophyll and the underside of leaves, often leaving the veins and upper epidermis intact, with the edges of the feeding holes irregular and wavy. In severe cases, no intact leaf remains in the licorice field; the remaining leaves of damaged licorice turn yellow, wither, and fall off, seriously affecting photosynthesis and causing poor plant growth. The main damage period is from mid-July to late August. It produces 2-3 generations per year and overwinters as adults in grass clumps, under plant debris, in soil clods, and in soil cracks.

Control methods: From May to June, when the overwintering generation population density is relatively high, use 4.5% methyl parathion-trichlorfon powder or 2.5% trichlorfon powder for control, applying about 2.5 kg per mu. During the peak outbreak period, spray 2.5% deltamethrin at 2000-4000 fold dilution for contact killing. Before overwintering, clear away residual branches and fallen leaves in the field, and use irrigation and other methods to kill overwintering insect sources, reducing the overwintering survival rate to achieve control objectives.

Ningxia ground pearl scale (Porphyrophora ningxiana)

This insect is a piercing-sucking pest of licorice roots. In addition to severely damaging wild licorice, it also causes devastating damage to cultivated licorice in Inner Mongolia, Ningxia, Gansu, and other regions. This insect has one generation per year, overwintering as newly hatched nymphs in the root zone of the host. In its life cycle, only the adult stage briefly moves above ground; all other stages live underground. The main damage period is from early May to early August each year. During the damage period, spherical red pearl bodies covered with a waxy shell can be seen on the host rhizomes. Because the damage period is early and occurs underground, it is not easily detected and is difficult to control. It often causes rhizome rot after damage, leading to large-scale plant death.

Control methods: The period from late March to early May, when overwintering nymphs are searching for hosts, and the period from early to late August, before adults mate and lay eggs, are the optimal times for chemical control. In the early stage, systemic insecticides can be applied by trench irrigation; in the later stage, dusting or spraying for contact killing can achieve good control results. In artificial cultivation, attention should be paid to the selection of habitat types to avoid devastating damage. Timely and reasonable harvesting of licorice is also one of the important methods to prevent pest-related losses.

Leafhoppers

The main species are the elm leafhopper (Empoasca ulmicola) and the small green leafhopper (Empoasca flavescens), which mainly damage licorice leaves. They are distributed in all licorice-producing areas, with large populations and a long damage period. In severely affected fields, the functional leaves in the lower part of the plant turn yellow and fall off prematurely, while the functional leaves in the middle and upper parts turn from green to yellow, seriously affecting growth and potentially causing premature leaf drop and dormancy 1 month early. The severe damage period is from mid-June to mid-August. After September, when licorice begins to turn yellow and wither, they can be seen clearly migrating to other hosts to prepare for overwintering. This insect produces 4-5 generations per year and overwinters as eggs in bark crevices and between branches. Damage by this insect can be seen throughout the licorice growing period.

Control methods: Experiments have shown that using 2.5% deltamethrin emulsion at 1000, 2500, and 5000 fold dilutions, applied at 45 kg per mu, the control effects 14 hours after application were 96.6%, 97.9%, and 95.3% respectively; in production, 2000-4000 fold dilution can be used for timely control. To prevent pest damage, cultivated licorice should avoid excessive water and fertilizer that causes tender, rank growth, and overwintering hosts such as elm trees should be removed.

Aphids

The main species are the black aphid (Aphis craccivora) and the green peach aphid (Myzus persicae). This insect is widely distributed, producing 8-12 generations per year, and overwinters as eggs in tree branches and crevices, and can also overwinter in the root zone of perennial plants. The degree of damage varies greatly between different years and different habitats. In normal years, the damage period is short, mostly affecting individual plants from late June to early July, and is rarely seen at other times.

Control methods: In normal years, natural enemies such as ladybugs and lacewings can be used to control the damage without the need for chemical control. At the same time, attention should be paid to clearing weeds along field edges and canal-side forest areas. In years with severe damage, early control should be implemented, taking care to allow aphid-eating natural enemies to exert their control capacity. Short-acting insecticides such as deltamethrin, dimethoate, and monocrotophos should be used as the main chemical agents.

Short-haired weevil (Phytoscaphus sp.)

This insect is a small green weevil that feeds on licorice stems and leaves. It has a long damage period and can generally be seen in licorice fields from May to September. The peak damage period is from July to early August. It mainly feeds on leaves, leaving notched edges after feeding. It produces 2-3 generations per year and overwinters as adults or early-instar larvae in bark crevices and in the root zones of licorice and weeds. The occurrence of this pest does not have strict humidity requirements; a relative humidity of 20%-50% is favorable for reproduction.

Control methods: 2.5% deltamethrin emulsion at 1000, 2500, and 5000 fold dilutions, applied at 45 kg per mu, can achieve satisfactory control effects, with control rates of 98.0%, 91.8%, and 88.3% respectively. In addition, combining weed clearing in autumn to destroy its overwintering sites and reduce the overwintering population base can also have a preventive effect. In developing licorice production, avoiding planting under forest canopies or near forest belts is one way to reduce damage from pests such as the short-haired weevil.

Plant bugs (Miridae)

The main species are the alfalfa plant bug (Adelphocoris lineolatus), the three-spotted plant bug (Adelphocoris fasciaticollis), and the lucerne bug (Adelphocoris suturalis). They produce 3-4 generations per year. The alfalfa plant bug overwinters as adults in weeds in fields, in bark cracks, under fallen branches and leaves, and in the root zone of hosts. Other plant bugs overwinter as eggs in the residual stems of hosts such as licorice and alfalfa, and in bark cracks. They are distributed in all licorice-producing areas. The peak damage period is from July to early August. The damage symptoms are similar to those of leafhoppers, but the white spots are larger, and the leaves mostly show silver-white chlorosis. They often occur mixed with leafhoppers. In cultivation, attention should be paid to density and water and fertilizer management to prevent habitats that could lead to explosive outbreaks.

Control methods: In autumn and winter, clear away residual branches and fallen leaves in and around the field. In late spring, clear weeds in a timely manner. At the same time, strictly manage water and fertilizer, and thin seedlings appropriately to make plants grow robustly and reduce pest occurrence. When pest populations are too large, conventional pesticides can be used to control them together with leafhoppers in a single application.

Licorice seed beetle (Acanthoscelides sp.)

This insect produces one generation per year and overwinters as larvae inside licorice seeds. It begins to emerge in late May and mainly feeds on licorice seeds during storage. Adults can also feed on licorice leaves. If seeds are not treated in the same year, the infestation rate can reach 35% after overwintering, and can reach 77.4% after 2 years of storage.

Control methods: Field surveys show that adults can be seen in the field from late May to late September, with the highest population density in early August. The focus of control is during the pod-setting period (seed production bases) and the seed storage period. Seed treatment at the storage stage is convenient and efficient and is the optimal period for controlling damage. Generally, fumigation with aluminum phosphide or other chemicals, or seed dressing with methyl parathion-trichlorfon powder, 165 powder, or other chemicals before storage can achieve good results.

Larvae overwinter in dead branches.

Control methods: Pay attention to cutting grass before winter to eliminate overwintering insect sources, and promptly remove damaged plants.

Underground pests

In addition to the above-ground pests mentioned above, whether licorice production can develop rapidly and achieve good economic benefits at the current stage largely depends on the control of underground pests. In addition to the Ningxia ground pearl scale, during the seedling emergence stage there are also mole crickets and the ground beetle (Harpalus sp.), and during the mature plant stage there are mainly the black wrinkled chafer (Trematodes tenebrioides), the yellow-brown chafer (Anomala exoleta), wireworms, white grubs, cutworms, and darkling beetles, which cause serious damage to licorice production.

Wild and cultivated licorice differ greatly in losses after being damaged by underground pests. Wild licorice has root heads deep below the soil surface; the main part damaged by feeding is the underground stem, and after damage, adventitious buds can grow rapidly and regenerate, so the whole plant does not rot and die. However, in cultivated licorice, the main part damaged by feeding is the root; the plants are young and have weak recovery ability, and with rot infection, the entire plant often rots and dies. Therefore, it is difficult to maintain seedling survival in 1-3 year old cultivated licorice. This is the main reason why underground pests such as the Ningxia ground pearl scale and white grubs cause large-scale seedling shortage and death in cultivated licorice.

Control methods: (1) Before sowing, select habitats and regions with light underground pest pressure and unfavorable conditions for their occurrence. (2) Finely prepare the soil, deep plow and heavy harrow to destroy their habitat and kill the insects. (3) Apply decomposed manure to prevent white grubs and other pests from being artificially introduced into licorice fields. (4) Emphasize pre-sowing seed soaking and dressing treatment; 40% isofenphos-methyl at 0.2% (of seed weight), 50% parathion (1605) emulsifiable concentrate at 0.2%, 25% phoxim emulsifiable concentrate at 0.1%, etc., can be used for seed dressing. (5) When underground pest populations are relatively large, spray 2% phoxim powder at 5 kg per mu before plowing, or use methyl parathion-trichlorfon powder or 1605 powder for pre-sowing soil treatment. (6) Harvest 3-5 year old licorice in a timely manner.

In order to meet the quality standards for pollution-free medicinal materials, spraying toxic pesticides or other chemical agents is prohibited within 45-60 days before licorice harvest to prevent pesticide or harmful heavy metal residues in licorice medicinal materials from exceeding standards.