Common Pests and Diseases of Chinese Medicinal Materials and Their Control
Release Date:
2021-06-01
Plant Diseases
When plants are infected by harmful organisms or subjected to adverse environmental conditions, their normal physiological processes are disrupted, leading to abnormal physiological and morphological symptoms; this condition is referred to as a plant disease.
The main causes of plant diseases can be summarized as follows:
1. Diseases caused by biological factors that are contagious and involve an infection process are referred to as infectious diseases, also known as contagious diseases.
2. Diseases caused by abiotic factors include adverse physical and chemical conditions, such as nutrient deficiencies or excesses, imbalances in water supply, excessively high or low temperatures, insufficient or excessive sunlight, the presence of toxic gases in the air, and phytotoxicity resulting from improper pesticide application. Since diseases induced by abiotic factors are not contagious, they are referred to as non-infectious diseases or physiological disorders.
I. Common Diseases and Control Measures for Chinese Medicinal Materials
1. Root Rot
In the early stages of the disease, the fibrous roots and lateral roots first turn brown and rot, gradually spreading to the taproot and eventually causing complete root rot, followed by downward-to-upward wilting of the aboveground stems and leaves and eventual death of the entire plant.
This disease is often associated with damage caused by underground nematodes and root mites. Additionally, it tends to be more severe in heavy, clayey soils with excessive waterlogging in the field. Among medicinal herbs, Scutellaria baicalensis, Salvia miltiorrhiza, Isatis indigotica, Astragalus membranaceus, Pseudostellaria heterophylla, Paeonia lactiflora, and Codonopsis pilosula are particularly susceptible to this disease.
Control measures: Disinfect the soil before sowing, apply insecticides to control underground pests, and increase the application of well-rotted organic fertilizer to enhance disease resistance. In the early stages of the disease, irrigate the roots with a 800–1,000-fold solution of thiophanate-methyl or carbendazim, and ensure timely drainage after rainfall.
2. Powdery Mildew
In the early stages, nearly circular, white, powdery spots appear on both surfaces of the leaves; as the disease progresses, these spots coalesce into large, ill-defined, whitish-powdery patches. In severe cases, the entire leaf or even the whole plant becomes completely covered with a layer of white powder. The pathogen not only attacks the leaves but also the stamens, pods, and stems. Later, the powdery coating turns grayish-white, and numerous small black granules develop within the fungal mass—these are cleistothecia. By autumn, the incidence in Astragalus fields often exceeds 70%, and in severe cases, premature defoliation occurs, leading to yield losses.
Control and prevention methods
1) When planting, it is advisable to choose a fresh crop rotation, with grasses being the preferred preceding crop; continuous cropping should be avoided.
2) Implement appropriate planting density and enhance ventilation and light penetration in the field;
3) Given the overwintering habit of the A. mongolica powdery mildew pathogen on dead branches and fallen leaves, after harvesting the aboveground parts of Astragalus, sweep up the remaining branches and leaves and burn them in a centralized location to reduce the overwintering inoculum.
4) Conduct timely intertillage and weeding in the early growth stage, and implement appropriate fertilization and irrigation management in the mid-growth stage to enhance plant disease resistance.
3. White Silk Disease
It commonly occurs at the roots or stem base near the soil surface, where a layer of white, silk-like mycelium develops; in severe cases, the tissue rots into a tangled, matted mass, ultimately leading to leaf wilting and eventual death of the entire plant.
The disease is particularly severe during hot, humid seasons or under conditions of soil waterlogging. Key medicinal herbs susceptible to this disease include Astragalus, Platycodon, Atractylodes, Pseudostellaria, and Glehnia.
Control measures: Rotate with gramineous crops or alternate between paddy and upland cultivation; disinfect the soil with lime before sowing, or treat seeds with a solution of carbendazim or thiophanate-methyl.
4. Damping-off
It primarily occurs during the seedling stage, initially manifesting as brown lesions at the base of the seedling stem that expand into stem-rot lesions. The affected areas lose water and shrivel, leading to widespread wilting and death of the seedlings.
The medicinal materials most commonly affected include Astragalus, Eucommia, Ginseng, Notoginseng, Atractylodes, Glehnia, Saposhnikovia, and Chrysanthemum, among others.
Control measures: disinfect the soil, improve cultural practices to lower soil temperature; upon disease onset, promptly remove infected plants and treat the soil with carbendazim, pentachloronitrobenzene, or similar fungicides, while also applying foliar sprays to prevent infection of healthy plants.
5. Wilt Disease
Plant diseases primarily caused by fungi or bacteria often have an abrupt onset, with symptoms including severe spotting, wilting, or the death of leaves, flowers, fruits, stems, or even the entire plant.
In the early stages of the disease, the lower leaves lose chlorophyll, then turn yellow and eventually wither and die; the disease is particularly severe in fields under continuous cropping and on poorly drained clay soils. Medicinal plants such as Astragalus, Platycodon, and Schizonepeta are frequently affected by this disease.
Control methods: Rotate crops with gramineous species, and at the early stage of disease onset, apply fungicides such as carbendazim and thiophanate-methyl for control.
6. Downy Mildew
The undersides of the leaves are covered with a frosty, mold-like layer that is initially white, later turning grayish-black, ultimately leading to yellowing and necrosis of the leaves. The disease is more severe during cool, rainy, and humid conditions in early spring or late autumn.
The medicinal materials most affected are Isatis root, Corydalis rhizome, Codonopsis root, goji berries, Glehnia root, and chrysanthemum, among others.
Control methods: Apply fungicides such as 40% ethyl phosphonate, aluminum ethyl phosphonate, metalaxyl, and thiophanate-methyl by spraying.
7. Leaf Spot Disease
During disease onset, necrotic spots appear on the leaves, varying in size and shape. Medicinal herbs susceptible to leaf spot disease include Platycodon grandiflorus, Salvia miltiorrhiza, Lonicera japonica, Lycium barbarum, Pseudostellaria heterophylla, Chrysanthemum morifolium, and Angelica dahurica, among others.
Control and prevention: Apply fungicides such as carbendazim and zinc dithiocarbamate promptly.
8. Rust Disease
During disease development, yellow or rust-brown pustules and bristle-like structures appear on leaf lesions; when these rupture, they release a rust-colored powdery substance. The disease is particularly severe during prolonged periods of overcast and rainy weather.
Medicinal materials prone to rust disease include honeysuckle, astragalus, northern adonis, angelica root, atractylodes, codonopsis, papaya, and corydalis, among others.
Control methods: Timely spraying with triadimefon, zinc dithiocarbamate, and carboxin is effective.
II. Common Insect Pests of Chinese Medicinal Materials and Their Control
A wide variety of animals can harm medicinal plants, with insects being the primary group; other harmful organisms include mites, snails, and rodents. Although many insects are pests, some are beneficial and should be protected, bred, and utilized.
Different insect species have varying mouthparts due to differences in their diets and feeding habits, with the main types being chewing mouthparts and piercing-sucking mouthparts. Insects with chewing mouthparts include beetles, grasshoppers, and the larvae of moths and butterflies. These pests feed on solid plant tissues, damaging roots, stems, leaves, flowers, fruits, and seeds and causing mechanical injury such as notching, perforation, breakage, boring into stems, and severing roots. Insects with piercing-sucking mouthparts include aphids, stink bugs, leafhoppers, and mites. They use needle-like mouthparts to pierce plant tissues and suck sap, resulting in symptoms such as wilting, leaf curling, leaf rolling, necrotic spots, loss of growth points, and gall formation (caused by salivary stimulation). In addition, there are also siphoning mouthparts (as found in moths and butterflies), lapping-sucking mouthparts (as seen in flies), and chewing-sucking mouthparts (as in bees).
1. Aphids
This insect pest occurs from May to September. It comprises numerous species with diverse morphologies and body colors, including yellow, green, black, brown, and gray. The pests congregate on tender leaves, shoot tips, and flower buds, feeding on plant sap, which leads to plant wilting, growth cessation, yellowing and drying of leaves, and impaired flowering and fruiting. A wide range of medicinal plants are susceptible to this pest, with nearly all medicinal species being affected.
Control methods: Thoroughly clean the medicinal herb garden, remove weeds to reduce overwintering insect eggs and eliminate opportunities for infestation. During the outbreak period, spray with a 2,000-fold dilution of cypermethrin solution, or a 1,500-fold dilution of omethoate, or a 1,000-fold dilution of 50% malathion.
2. Red Spider Mite
This pest outbreak occurs in July and August. It comprises several species, all small and red in color, and typically feeds on leaf sap on the underside of leaves. In the early stages, affected leaves turn reddish-yellow; as the infestation progresses, the damage becomes severe, leading to complete desiccation of the entire leaf, with flowers, leaves, and fruits all being simultaneously damaged.
The pest exhibits extremely high reproductive capacity, and the main affected crops include Fritillaria cirrhosa, fenugreek, licorice, burdock, Panax notoginseng, Angelica sinensis, Rehmannia glutinosa, safflower, Ligusticum chuanxiong, Citrus aurantium immaturus, and Platycodon grandiflorus, among others.
Control methods: During the occurrence period, spray with a 1,500-fold dilution of dimethoate, dichlorvos, or lime-sulfur mixture.
3. Scale Insects
In July and August, insect infestations occur, often quite severe. The females secrete a waxy coating or filamentous substances and remain firmly attached to branches, leaves, or fruits, where they feed on sap, gradually causing the entire plant to wither and die.
Control measures: Thoroughly clean the medicinal garden, remove weeds, improve ventilation and light penetration within the garden, and thereby reduce pest damage. During the outbreak period, spray with an 80% dichlorvos or fluoroacetamide solution diluted 1,500–2,000 times.
4. Cabbage White Butterfly
This pest occurs from May to September. The larvae (cabbage worms) damage flower buds and leaves, causing holes and notches; in severe cases, the leaves are completely defoliated.
Control methods: manual removal and destruction; during the larval stage, spray with an 800-fold dilution of 90% trichlorfon.
5. Cutworm
This pest outbreak occurs in May and June. The larvae are soil-dwelling pests that feed on young roots and seedlings at night, causing the plants to gradually wilt and eventually die.
The main species susceptible to damage include: Chinese yam, peony, goji berry, phellodendron bark, fenugreek, angelica, codonopsis, bupleurum, atractylodes, rehmannia, lithospermum, aster, and fritillaria cirrhosa, among others.
Control methods: Apply toxic bait before sowing; drench the roots with a 500–600-fold dilution of phoxim or a 700–1,000-fold dilution of trichlorfon; or spray with an 80% dichlorvos solution diluted 600 times or a trichlorfon solution diluted 700–1,000 times.
6. Grub
Larval damage is the most severe. Larvae primarily feed on roots and underground stems, with lesser damage to aboveground parts. Adult beetles, known as Japanese beetles, mainly damage the aboveground portions of plants.
A wide variety of medicinal plants are susceptible to damage, including Dioscorea nipponica, ginseng, Pseudostellaria heterophylla, Fritillaria ussuriensis, Bupleurum, Ophiopogon, Chinese yam, Angelica sinensis, Lithospermum, Veronicastrum, Codonopsis, Paeonia, Carthamus, Gentiana, and others.
Control methods: Japanese beetles are attracted to light; at night, black-light traps can be set up in the orchard for mass trapping and killing. Alternatively, a 600–800-fold dilution of dichlorvos or dimethoate can be sprayed.
7. Root-knot Nematode Disease
Due to parasitism by root-knot nematodes, numerous galls develop on the roots, resulting in stunted plant growth, yellowing leaves, and ultimately the death of the entire plant.
The medicinal materials most severely affected by this disease include citrus, with particularly severe infections observed when trifoliate orange and red mandarin are used as rootstocks, while acid citrus and sour orange rootstocks exhibit milder symptoms; other affected species include Salvia miltiorrhiza, Platycodon grandiflorus, Astragalus membranaceus, Panax ginseng, and Glehnia littoralis.
Control measures: It is best to rotate with gramineous crops or alternate between paddy and upland cultivation, and to disinfect the soil before sowing by applying methyl isofenphos or similar agents.
III. Integrated Pest and Disease Management for Medicinal Plants
I. Agricultural Control Methods
Agroecological control refers to a set of measures, including adjustments to cultivation practices, aimed at reducing or preventing pest and disease outbreaks. These measures are predominantly preventive and primarily encompass the following aspects:
1. Rational crop rotation and intercropping
In medicinal plant cultivation systems, implementing appropriate crop rotation and intercropping is crucial for both the control of pests and diseases and the efficient utilization of soil fertility. For example, many soil-borne diseases pose a severe threat to ginseng and American ginseng. Fields previously planted with these crops should not be replanted in the short term; otherwise, disease incidence will be so high that it can lead to massive plant mortality or even total crop failure. The length of the rotation period is generally determined by how long the pathogenic organisms can survive in the soil—for instance, the rotation period for root rot of Atractylodes and wilt of Rehmannia is typically 3 to 5 years. In addition, the rational selection of rotation crops is of paramount importance: plants belonging to the same family or genus, or those that serve as hosts for the same serious pests or diseases, should generally not be chosen as the subsequent crop. The principles guiding the selection of intercrop species should be essentially the same as those for rotation crops.
2. Deep Tillage
Deep tillage is an important cultivation practice that not only promotes root development and enhances plant disease resistance, but also disrupts the overwintering habitats of soil-dwelling pest larvae and pathogenic fungi, thereby directly eliminating these pathogens and pests. For example, in the cultivation of ginseng and American ginseng, the land is typically left fallow for one year prior to sowing, followed by multiple ploughings and exposures to sunlight, to improve soil physical properties and reduce the population of soil-borne pathogens; this has become one of the key preventive and control measures.
3. Weeding and pruning
After harvesting weeds and medicinal plants from the fields, the remnants of plants damaged by pests and diseases, as well as dead branches and fallen leaves that have dropped onto the field, often serve as hiding places and overwintering sites for these pests and pathogens, thereby becoming sources of infestation in the following year. Therefore, thorough weeding, field sanitation, and the simultaneous removal and destruction or deep burial of pest- and disease-damaged plant residues and dead organic matter through pruning can significantly reduce the severity of pest and disease damage in the subsequent growing season.
4. Adjusting the Sowing Date
Certain pests and diseases are often closely associated with specific phenological stages of a crop’s growth and development. By deliberately timing cultural practices to avoid these critical periods of high pest and disease pressure, it is possible to prevent or mitigate damage and thereby achieve effective control.
5. Rational Fertilization
Appropriate fertilization can promote the growth and development of medicinal plants, enhancing their resistance and ability to recover after damage caused by pests and diseases. For example, applying sufficient organic fertilizer to Atractylodes macrocephala, combined with appropriate supplemental applications of phosphorus and potassium fertilizers, can reduce the incidence of mosaic disease. However, any farmyard manure or compost used must be fully decomposed; otherwise, residual pathogenic microorganisms and pest eggs, such as those of grubs, will remain viable and may exacerbate underground pest infestations and certain diseases.
6. Breeding and utilization of disease- and pest-resistant medicinal plant varieties
Different types or varieties often exhibit markedly varying resistance to diseases and pests. For example, spiny safflower is more resistant to anthracnose and the safflower fruit fly than spineless safflower, and the dwarf cultivar of Atractylodes macrocephala is more resistant to the Atractylodes seed weevil. Therefore, harnessing these disease- and pest-resistant traits to further select and breed superior, high-yielding varieties with enhanced resistance represents a highly meaningful endeavor.
II. Physical Control Methods
This method involves the use of various physical factors and equipment to control pests and diseases. For example, light traps can be used to lure and kill pests by exploiting their phototaxis; since seeds infected with pests and diseases are generally lighter than healthy seeds, methods such as air separation and water flotation can be employed to remove contaminated seed; additionally, seed soaking in warm water is another effective practice.
III. Biological Control Methods
Biological control is a method that uses various beneficial organisms to manage plant diseases and pests. It primarily encompasses the following aspects:
1. Utilizing parasitic or predatory insects
Biological control using insects involves the use of parasitic insects, which can be either endoparasites or ectoparasites. These parasites are artificially bred and then released into fields to reduce pest populations. Predatory insects include mantises, aphid lions, and ground beetles, among others. Such predators primarily feed on pests and play a crucial role in suppressing pest numbers. Large-scale breeding and release of these beneficial insects can effectively control pest outbreaks.
2. Microbial Control
Utilize fungi, bacteria, and viruses that parasitize pest insects, causing them to become diseased and die or inhibiting their damage to plants.
3. Animal Control
Utilize beneficial birds, frogs, chickens, ducks, and other species to control pest populations.
4. Applications of Sterile Insects
By exposing pests to radiation or chemical treatments, their reproductive capacity is impaired, preventing them from producing offspring and thereby achieving the goal of pest eradication.
IV. Chemical Control Methods
This refers to the use of chemical pesticides for the control of plant diseases and insect pests. Its main advantages are rapid action, high efficacy, ease of application, and the ability to quickly eliminate or bring under control large-scale outbreaks of pests and diseases within a short period of time, without being constrained by regional or seasonal factors. It is currently an important means of pest and disease control, and no other control method can yet fully replace it. Chemical pesticides include insecticides, fungicides, nematicides, and others. Insecticides, according to their mode of action, can be further classified into stomach poisons, contact poisons, systemic agents, and fumigants; fungicides include protectants and curative agents. There are numerous methods for applying pesticides, including spraying, dusting, seed dressing, seed soaking, fumigation, and soil treatment.
The insect cuticle consists of three layers: the epidermis, the cuticular cells, and the basal lamina. The epidermis, in turn, is divided from inside to outside into the endocuticle, the exocuticle, and the epicuticle. The epicuticle is the outermost and thinnest layer of the cuticle; it contains waxy or similar substances and plays a crucial role in preventing water loss from the body as well as the penetration of chemical agents.
In general, as insects age, the resistance of their cuticle to pesticides steadily increases. Therefore, pesticides often contain solvents that can dissolve fats and waxes; for example, emulsifiable concentrates, which include highly soluble oils, typically exhibit greater toxic efficacy than wettable powders. Pesticides enter pest bodies primarily through three routes: the mouthparts, the cuticle, and the spiracles. Consequently, selecting appropriate formulations based on the structural characteristics of the insect cuticle is crucial for enhancing control effectiveness. For instance, chewing-mouthpart pests such as the corn borer, swallowtail caterpillars, and cabbage worms should be targeted with stomach-poison agents like trichlorfon, whereas piercing-sucking pests are best controlled with systemic insecticides. In addition, it is essential to understand the occurrence patterns of pests and diseases, identify optimal timing for intervention, and apply pesticides promptly. Furthermore, pesticides should be used in a rational, alternating, and safe manner to prevent phytotoxicity and poisoning of humans and livestock.
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