What pests and diseases affect Zanthoxylum bungeanum (Sichuan pepper) trees in 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 Sichuan pepper trees? What are the control methods for pests and diseases?

During the growth and development of Sichuan pepper, due to unsuitable environment or infection by pathogenic fungi, diseases often occur that affect tree growth, fruit setting, and product quality. Common diseases: rust disease, anthracnose, gummosis, spot leaf drop disease, dry rot, leaf spot disease, felt fungus disease, etc.; Common pests: red spider mite, brevipalpus mite, scale insects, aphids, fruit borers, jewel beetles, swallowtail butterflies, snails, longhorn beetles, etc.

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 and rotten in appearance, the diseased bark becomes sunken, and gum exudes. The lesions turn black and elongate-oval. When the diseased bark is peeled back, white mycelium can be seen distributed in the affected tissue. In the later stage, the lesions shrink, crack, and numerous orange-red small dots appear. Black granules are often produced 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, increase application of organic fertilizer, enhance tree vigor, carry out frost prevention, pest prevention, and sunscald prevention well, reduce pathogen invasion, and prune timely to remove diseased branches, using pest control to promote disease prevention. Use the scraping method, i.e., scrape off the lesions at the affected parts with a blade to the xylem, then apply 50% thiophanate 500x solution to the wound. From April to May each year and after harvesting pepper, spray the entire orchard with 1:1:100 Bordeaux mixture or “Daqingyuan” and thiophanate, or 80% antibiotic (402) 100x solution for control.

2. Sichuan Pepper Rust Disease

Generally begins to occur in mid-to-late June, with July-September being the peak period. 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 leaves. As the lesions expand, yellow-brown structures appear, arranged in a ring pattern.

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

3. Anthracnose

This disease mainly damages fruits. 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 sunken centers. It begins to occur from late June to late July each year, with August entering the peak period.

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

4. Shoot Blight

This disease mainly damages the young shoots of current-year twigs. It is not obvious initially, but later the young shoots die, standing upright, and gray-brown elongated lesions appear on the twigs. Many black dots appear on the lesions, with the epidermis slightly raised. It begins to occur in late June, with July-August being the peak period.

Control methods: When blighted shoots are found, cut them off 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 to occur at 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 yellow-brown gum, hence the name gummosis. Affected pepper trees first die locally, then gradually expand until the whole tree dies. The main causes of gummosis are damage by longhorn beetle and jewel beetle larvae, frost damage, and trunk cracking.

Control methods

① Strengthen cultivation management of trees to enhance disease resistance. Increase application of organic fertilizer and improve soil. Since some pests and diseases mainly invade through wounds, underground pests and diseases should be promptly controlled by root irrigation. Avoid damaging large roots during deep plowing to reduce non-infectious diseases.

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

③ Clean the orchard and disinfect to reduce overwintering pathogens and pests. Winter cleaning of the Sichuan pepper orchard should be thorough, with diseased branches and leaves gathered and burned or deeply buried. Spray once each in early spring and late autumn with 5 degree Baume lime sulfur mixture or 100x equal-amount Bordeaux mixture to control overwintering diseases. Whitewash the trunk before winter to prevent frost damage. In addition, promptly replace the surface soil 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, attached to the tree. The fungal membrane tissue can reach about 6.7-10 cm in diameter. It is initially grayish-white, light brown, or yellow-brown, later turning purplish-brown, dark brown, or rusty brown; sometimes it appears velvety, with lighter edges and often cracked centers; some shrink and gradually peel off in the later stage. The entire fungal membrane looks like a plaster in traditional Chinese medicine, hence the name “felt fungus disease” (plaster 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 chemical injection or high-concentration strong-penetration chemicals are used to brush the diseased parts. The most commonly used chemicals are spraying Bordeaux mixture or 20% lime milk; of course, widespread spraying is somewhat too costly and may also kill some natural enemies of scale insects. To effectively control felt fungus disease, we generally only manually remove the diseased parts of affected plants and apply 4-5 degree Baume lime sulfur mixture. Because 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 disease pathogen, to control felt fungus disease, we must first control scale insects well. The control of scale insects and the methods and dosages of chemicals used vary in different seasons and periods. Scale insect control can follow the methods described above.

II. Control of Sichuan Pepper Pests

1. Sichuan Pepper Scale Insect

This pest mainly damages the young 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 eclosion. The main egg-laying site is on the underside of leaves. Late April is the peak egg-laying period. The egg stage lasts 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 “Jieqiao Susha” or “Jiesijing” 800-1000x solution; spray “isocarbophos” 1500x + equal amount of “Hailiping”; spray “Supumie” 1000x. Egg stage (late April to mid-May): spray “isocarbophos” 1500x + equal amount of “Hailiping”. Nymph stage (late June to late October): spray “Jieqiao Susha” or “Jiesijing” 800x solution; spray “Mieshaoli” 2000x solution; spray “isocarbophos” 1500x + equal amount of “Hailiping”. Overwintering stage: During tree dormancy, spray 3-5 degree Baume 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 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 enters the peak larval hatching period. The larval stage lasts over 10 months. April and June are the periods of severe damage.

Control methods: From late April to early May during the gum-flowing period of overwintering larvae and in early June during the gum-flowing period of newly hatched larvae boring, use a hammer, stone, etc. to strike the gum-flowing areas to crush the larvae to death. Then use a small knife to scrape off the dried, cracked, rotted, or larger gum scars at the gum-flowing areas together, scraping down to healthy bark, then apply 20-50x “Supumie”.

From mid-May to late June, spray the canopy with fenvalerate, deltamethrin, etc. at 800-1000x solution, once every 7 days, continuously 2-3 times to kill adults; in June during the peak larval hatching period, use 50-100x “Supumie” for trunk painting, once every 7-10 days, continuously 2-3 times, to kill newly hatched larvae.

3. Aphids

This pest can generally reproduce 20-30 generations per year. It overwinters as eggs parasitic on Sichuan pepper trees. After hatching in March of the following year, the nymphs reproduce 2 to 3 generations on the tree, then produce winged viviparous aphids. Winged aphids fly to cotton fields or other host trees from April to May to produce offspring and cause damage. 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 a sweep net in the morning to capture seven-spot ladybird adults and larvae in wheat fields, and release them back onto pepper branches. The ladybird-to-aphid ratio is 1:200. You can also spray artificial honeydew or sucrose solution on pepper trees to attract seven-spot ladybirds and other natural enemies.

Chemical control: A sprayer filled with 15 kg of water, with the following chemicals mixed per tank: 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 chemical application method: Time is early to mid-March. At 20-30 cm from the trunk base, scrape off old bark, apply systemic pesticide in a 15-20 cm wide band, then wrap with newspaper or kraft paper.

For example, the formula 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 dorsal side. This butterfly has spring and summer forms. The summer form is large with deep yellow coloration; the spring form is small. Newly hatched larvae are black-brown with yellow heads; when mature, the entire body is green.

2. Life habits: 2——3 generations per year, overwintering as pupae. Adults emerge and lay eggs in March. After hatching, they feed on young leaves with a large appetite, sometimes eating all leaves on a plant, leaving only the main vein of old leaves. They mature and pupate in May. 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 swallowtail butterflies is relatively simple. Once found, spray with cyhalothrin, emamectin benzoate, emamectin chlorbenzuron, bifenthrin, etc. for control.