What pests and diseases affect the Sichuan pepper tree (Zanthoxylum bungeanum) of the Rutaceae family, and what are the symptoms and control methods?

Sichuan pepper is a tree species with high economic value, possessing high medicinal and edible value, and is an important plant. So what diseases affect the Sichuan pepper tree? What are the pest and disease control methods?

During the growth and development of Sichuan pepper, due to unsuitable environmental conditions or invasion by pathogenic bacteria, diseases often occur that affect the tree's growth, fruit setting, and product quality. Common diseases include: rust, anthracnose, gummosis, spotted leaf drop, dry rot, leaf spot, and felt fungus disease; common pests include: red spider mite, hemisarcoptid mite, scale insects, aphids, fruit borers, jewel beetles, swallowtail butterflies, snails, and longhorn beetles.

I. Control of Sichuan Pepper Diseases

1. Dry Rot

In the early stage of the disease, the lesions are not obvious; the epidermis at the affected area turns reddish-brown. As the lesions expand, they become wet-rot-like, the diseased bark sinks, and gum exudes. The lesions turn black, elongated-oval. When the diseased bark is peeled back, white mycelium can be seen distributed in the diseased tissue. In the later stage, the lesions shrink, crack, and numerous orange-red dots appear. Black granules often form on old lesions. Large lesions can reach 5-8 cm in length, often causing large areas of bark to rot, and entire branches or the whole tree to die.

Control methods: Strengthen management, apply more organic fertilizer, enhance tree vigor, do a good job of frost protection, pest control, and sunscald prevention to reduce pathogen invasion, and prune promptly to remove diseased branches, promoting disease prevention through pest control. Use the scraping method, i.e., scrape off the lesions at the affected sites with a blade down to the xylem, then apply 50% thiophanate 500x solution to the wounds. In April-May each year and after harvesting the pepper, spray the whole orchard with 1:1:100 Bordeaux mixture or "Daqingyuan" and thiophanate, or 80% antibiotic (402) 100x solution for control.

2. Sichuan Pepper Rust

Generally, the disease begins in mid-to-late June, with the peak period from July to September. Leaves at the lower part of the canopy are affected first. In the early stage, circular dot-like pale yellow lesions appear on the underside of the leaves. As the lesions expand, they present a yellowish-brown appearance, arranged in a ring.

Control methods: In the early stage, spray once with an equal-amount 100x Bordeaux mixture. During the peak period, spray 65% zineb 500x solution 2-3 times, or spray 0.2 degrees Baumé lime-sulfur mixture.

3. Anthracnose

This disease mainly harms the fruit. In the early stage, several brown dots appear on the fruit surface, distributed irregularly. In the later stage, the lesions turn brown or black, circular or nearly circular, with a sunken center. The disease begins from late June to late July each year, and enters its peak in August.

Control methods: Strengthen orchard management and ensure good ventilation and light penetration in the orchard. In mid-June, spray once with 1:1:200 Bordeaux mixture or 50% thiram 800x solution. During the peak period, spray 1:1:100 Bordeaux mixture or mancozeb 800x solution.

4. Shoot Blight

This disease mainly harms the young shoots and tender tips of the current year. It is not obvious at first; later the tender tips die, standing upright, and grayish-brown elongated lesions form on the twigs. Many small black dots appear on the lesions, with the epidermis slightly raised. The disease begins in late June, with the peak period from July to August.

Control methods: When blighted shoots are found, prune and burn them promptly. During the disease period, spray 70% thiophanate 1000x, or 65% zineb 400x, or 40% asomate 800x.

5. Gummosis

Symptoms: This disease begins in the seedling stage and is more common in mature trees. Yellow mucus flows from the main trunk of the pepper tree and gradually increases, turning into yellowish-brown gum, hence the name gummosis. Affected pepper trees die first locally, then gradually the whole plant dies. The main causes of gummosis are damage by longhorn beetle and jewel beetle larvae, frost injury, and trunk cracking.

Control methods

① Strengthen cultivation management of the trees to enhance disease resistance. Apply more organic fertilizer and improve the soil. Since some pests and diseases mainly invade through wounds, underground pests and diseases should be promptly controlled by root irrigation. When carrying out deep plowing, avoid damaging large roots to reduce non-infectious diseases.

② Spray pesticides at the right time and take preventive measures. In late March when pathogens are about to emerge, spray 1500x thiophanate-methyl and other fungicides. Before the two peak disease periods, i.e., in mid-May and late July, spray water or scrape off the gum after rain, and spray 1000x chlorobromoisocyanuric acid or octilin (high concentration for trunk spraying only) every other week, alternating use, spraying 2-3 times continuously, to prevent the spread of infectious pathogens. When pests are severe, promptly use systemic agents (spirotetramat, thiamethoxam, etc.) applied to the trunk for control. For existing lesions, scrape them off promptly, then apply lime-sulfur mixture for protection. When borer holes are found on branches, promptly insert a steel wire or bamboo stick to pierce and kill the live borers, or plug the holes with a cotton ball dipped in 50x dichlorvos solution and seal the outside with soft mud to fumigate the borers to death.

③ Clear and disinfect the orchard to reduce overwintering pathogens and pests. Clean the Sichuan pepper orchard thoroughly in winter, burning or deeply burying diseased branches and leaves; spray once each in early spring and late autumn with 5 degrees Baumé lime-sulfur mixture or 100x equal-amount Bordeaux mixture to control overwintering diseases; whitewash the trunk before winter to prevent frost injury. In addition, promptly replace the topsoil around the tree base and root crown to reduce the occurrence of root and crown pests and diseases.

6. Felt Fungus Disease

Symptoms: Circular, oval, or irregular fungal membrane tissue forms on the trunk and branches, adhering to the tree. The fungal membrane tissue can reach about 6.7-10 cm in diameter. It is initially grayish-white, light brown, or yellowish-brown, later turning purplish-brown, dark brown, or internally brown; sometimes it is velvety, with lighter edges and often cracked centers; in some cases it later shrinks and gradually peels off. The entire fungal membrane resembles a medicinal plaster in traditional Chinese medicine, hence the name "felt fungus disease."

Control methods

① Chemical control and manual removal. Chemical control and manual removal are among the main methods for treating diseased plants. Felt fungus disease is a trunk disease caused by fungi. In terms of chemical control, generally pesticide injection or high-concentration, highly penetrative pesticide brushing of the diseased parts is used. The most commonly used agents are spraying Bordeaux mixture or 20% lime milk; however, widespread spraying is somewhat costly and may also kill some natural enemies of scale insects. To achieve effective control of felt fungus disease, we generally only manually remove the diseased parts of affected plants and apply 4-5 degrees Baumé lime-sulfur mixture. Since lime-sulfur mixture is a broad-spectrum fungicide, it not only kills the fungi causing felt fungus disease but also has a certain control effect on scale insects.

② Control of scale insects. Since the pathogen of felt fungus disease often coexists with scale insects, and scale insects can secrete a honeydew that provides nutrients for the growth and development of the felt fungus pathogen, to control felt fungus disease, the first step is to control scale insects well. The control of scale insects and the methods and dosages of pesticide use vary in different seasons and periods. Scale insects can be controlled according to the methods described above.

II. Control of Sichuan Pepper Pests

1. Sichuan Pepper Scale Insect

This insect mainly harms the tender buds of Sichuan pepper. In late February, newly hatched nymphs are orange-yellow and transparent, gradually turning flesh-red after feeding. In mid-April, female adults finish emerging. The main egg-laying site is on the underside of leaves. Late April is the peak egg-laying period, with the egg stage lasting about 15 days.

Control methods: Emergence period (late February to mid-April): Starting from early March, observe the field 2-3 times daily. When nymphs emerge in large numbers, begin spraying: spray "Jieke Susa" or "Jiesijing" 800-1000x solution; spray "isocarbophos" 1500x + an equal amount of "Hailiping"; spray "Supumie" 1000x. Egg stage (late April to mid-May): spray "isocarbophos" 1500x + an equal amount of "Hailiping." Nymph stage (late June to late October): spray "Jieke Susa" or "Jiesijing" 800x solution; spray "Mieshaoli" 2000x solution; spray "isocarbophos" 1500x + an equal amount of "Hailiping." Overwintering period: During the tree dormancy period, spray 3-5 degrees Baumé lime-sulfur mixture; "Weili Shamie" 800x; "Jiesijing" 800x solution.

2. Sichuan Pepper Narrow Jewel Beetle

One generation per year, overwintering as larvae in branches and xylem or under the bark. They begin activity in late April of the following year. Late April to late June is the peak pupation period. Late May to early July is the peak period for adult emergence from holes and egg-laying. Late June to early August is the peak larval hatching period. The larval stage lasts more than 10 months, with April and June being the periods of severe damage.

Control methods: During the gum-flow period of overwintering larvae from late April to early May and the gum-flow period of newly hatched larvae boring from early June, use a hammer, stone, or similar to strike the gum-flow sites to crush the larvae to death, then use a small knife to scrape off the dried, cracked, rotting, or larger gum scars at the gum-flow sites down to healthy bark, then apply 20-50x "Supumie."

From mid-May to late June, spray the canopy with pesticides such as fenvalerate or deltamethrin 800-1000x solution, once every 7 days, spraying 2-3 times continuously to kill adults; during the peak larval hatching period in June, apply 50-100x "Supumie" to the trunk, once every 7-10 days, spraying 2-3 times continuously, to kill newly hatched larvae.

3. Aphids

This insect can generally reproduce 20-30 generations per year, overwintering as eggs parasitizing on Sichuan pepper trees. In March of the following year, hatched nymphs reproduce 2-3 generations on the tree, then produce winged parthenogenetic aphids. The winged aphids fly to cotton fields or other host trees from April to May to produce offspring and cause damage. The aphids remaining on Sichuan pepper all migrate away after early June. In August, some winged aphids migrate from cotton fields or other host trees back to Sichuan pepper for a second feeding and damage.

Control methods: Biological control: Protect natural enemies. In early May, use an insect net in the morning to capture adult and larval seven-spotted ladybugs in wheat fields and release them back onto pepper branches, with a ladybug-to-aphid ratio of 1:200. Artificial honeydew or sucrose solution can also be sprayed on pepper trees to attract natural enemies such as seven-spotted ladybugs.

Chemical control: A sprayer holds 15 kg of water. Each tank is mixed with pesticides as follows: When pests occur in large numbers, compound pesticides can be used, namely: ① Supusha 8 mL + abamectin 4 mL; ② Huoshaoli 10 mL + abamectin 4 mL.

Urea-detergent mixture: urea (4): washing powder (1): water (400).

Trunk application method: Time is early to mid-March. At 20-30 cm from the trunk base, scrape off the old bark and apply systemic pesticide in a 15-20 cm wide band, then wrap with newspaper or kraft paper.

For example, the pesticide used is: Supusha (1): water (20).

4. Sichuan Pepper White Butterfly (also known as Citrus White Butterfly)

1. Morphological characteristics: Adult body length 18-30 mm, wingspan 66-120 mm, body yellow-green with black stripes on the back. This butterfly has two seasonal forms, spring and summer. The summer form is large with deep yellow coloration; the spring form is small. Young larvae are dark brown with a yellow head, turning entirely green when mature.

2. Life habits: 2-3 generations per year, overwintering as pupae. In March, adults emerge and lay eggs. After hatching, they feed on tender leaves with a large appetite, sometimes eating all the leaves on a whole plant, leaving only the main veins of old leaves. In May, they mature and pupate. Those occurring in June and July are the spring form; those occurring after July are the summer form.

Control of Sichuan Pepper Swallowtail Butterfly

Control of the swallowtail butterfly is relatively simple. Once found, spraying with cyhalothrin, emamectin benzoate, emamectin-chlorbenzuron, bifenthrin, or similar is effective.