What are the common pests of golden privet (Ligustrum vicaryi)? A detailed guide to control methods

Golden privet (Ligustrum vicaryi) is a semi-evergreen small shrub of the genus Ligustrum in the family Oleaceae. Because its young shoots are golden yellow and it tolerates pruning and drought, it is often combined with red-flowered Loropetalum (Loropetalum chinense var. rubrum), azaleas (Rhododendron) and Chinese juniper (Juniperus chinensis) to decorate flower beds and green belts. High-density planting often makes pest problems more severe, causing new shoots to grow slowly or not sprout at all, weakening the plants and even killing them. The common and most damaging pests of golden privet are: the citrus mealybug (Planococcus citri), the privet leaf-mining flea beetle, and the yellow-ringed silk-fringed pyralid moth.

1 Citrus mealybug

Adults and nymphs rest on the branches and leaves of golden privet and suck plant sap with their piercing-sucking mouthparts, causing the branches and leaves to lose water and wilt, and even die; they can also induce sooty mold.

1.1 Morphological characteristics

The adult body is flat and oval, pink, with white wax powder covering the surface; nymphs are oval, flat, pale yellow, also covered with white wax powder; eggs are oval, pale yellow, and the egg sac is white and cotton-like.

1.2 Life history and habits

In the Pingdingshan area, the citrus mealybug has 3 generations per year. Eggs overwinter in hidden places such as cracks in the host's branches and trunk, pruning and saw cuts, under loose bark, or in weeds, clods of soil and fallen leaves around the root zone. Hatching begins in early May of the following year. The peak hatching periods of the 3 generations are mid-to-late May, mid-to-late July and late August respectively; there is another small peak of damage in September, after which female adults lay eggs and overwinter.

1.3 Control measures

1.3.1 Change the environment and strengthen tree vigor Change or create environmental conditions unfavorable to mealybugs to reduce or weaken their damage. Densely planted golden privet is prone to mealybug damage, so planting density should be set reasonably to ensure good ventilation and drainage, and fertilizer and water management should be strengthened to enhance tree vigor and the plants' natural pest resistance.

1.3.2 Reduce pest sources In combination with pruning, cut off and burn severely infested branches to reduce pest sources and lower damage.

1.3.3 Chemical control Spraying an appropriate amount of pesticide during the peak hatching period of the first generation of mealybugs can greatly reduce pest damage for the whole year. Commonly used chemicals include: 40% omethoate at 1000 times dilution, and Jiemanling at 1000 times dilution; when the damage is severe, evenly spray Lorsban plus a penetrant for excellent results.

1.3.4 Use natural enemies The natural enemies of the citrus mealybug include green lacewings and various ladybugs, which should be protected and used.

2 Privet leaf-mining flea beetle

It mainly damages the leaves of golden privet. Adults feed on the leaves, causing round or irregular small spots on the leaves, while larvae burrow under the surface, tunneling curved mines beneath the epidermis, destroying the chloroplast structure, weakening photosynthesis, and causing large numbers of leaves to scorch, which affects the landscape effect of green spaces.

2.1 Morphological characteristics

The adult privet leaf-mining flea beetle is oval or round, black, with a metallic sheen on the back, and an oval red patch in the center of each elytron; larvae are pale yellow, thick and short, slightly flattened, with tumor-like protrusions on both sides of abdominal segments 1 to 8.

2.2 Life history and habits

In the Pingdingshan area there are 3 generations per year. Mature larvae overwinter in the soil, adults emerge in late April of the following year, the first generation occurs from May to mid-June, the second generation from late June to late July, and the third-generation larvae appear from late August to September.

2.3 Control measures

2.3.1 Physical control In early winter, remove lichens and moss from the trunk and seal trunk cracks to reduce overwintering sites; during the spring shoot growth period, pick off infested leaves and remove new fallen leaves, burning them in a centralized way, so as to kill the larvae before they enter the soil to pupate.

2.3.2 Chemical control During the damage period, spray Lorsban at 1000 times dilution plus a penetrant, or spray abamectin at 2000 times dilution or 40% omethoate at 8000 times dilution.

3 Yellow-ringed silk-fringed pyralid moth

The larvae roll leaves and feed on the leaf mesophyll of the host, leaving the epidermal tissue. It is characterized by concentrated outbreaks, large populations and devastating feeding. May to June is the period of severe larval damage; severely affected golden privet hedge plants turn scorched yellow, branches dry up, and leaves blacken, seriously affecting growth and the landscaping effect.

3.1 Morphological characteristics

The adult head is white, with the frons area covered with yellow scales; the base of the antennae is yellowish white and the rest white; the first segment of the labial palpus is white and the rest brown; the collar is brown; the body and wings are milky white with a silky sheen; the costal margin of the forewing has a broad yellow band, beneath which there are 3 pale yellow spots from the wing base to the end of the median cell. The mature larva is yellow-green, with a yellow-brown head and brown mouthparts; on the thorax, both sides of the dorsal plate of each segment and above the spiracle of the 8th abdominal segment each have a small black spot. The small spots are prismatic or tadpole-shaped. The pupa is green at first, turns green-brown after half a day, and becomes yellow-brown near emergence, with dark brown compound eyes and clearly visible wing markings. The posterior end of the abdomen has 8 anal spines; the tips of the anal spines are slightly curved and arranged in an arc. Eggs are flat and oval, tender yellow-green when first laid, and turn dark brown near hatching.

3.2 Life habits

In the Hengyang area of Hunan Province, this insect has 3 generations per year and overwinters as pupae in the soil near the host. Overwintering pupae begin to emerge and lay eggs in late April, and the first-generation larvae begin to hatch at the end of April; second-generation larvae begin to hatch in early June; third-generation (overwintering generation) larvae appear in early July and begin to enter the soil to pupate in mid-July.

3.3 Control methods

3.3.1 In late April, during the emergence period of overwintering-generation adults, spray the leaf surfaces and branches with 50% phoxim emulsifiable concentrate at 1000 to 1200 times dilution; in early May, spray the leaf surfaces with 40% omethoate emulsifiable concentrate at 1000 to 1200 times dilution to control larvae, with a control efficacy above 98%; in late May, spray the leaf surfaces and branches with 2.5% deltamethrin emulsifiable concentrate at 2500 to 3000 times dilution to control first-generation adults; in early June, spray the leaf surfaces with 40% omethoate emulsifiable concentrate at 1000 to 1200 times dilution to keep this pest under control.

3.3.2 From late April to early May and from late May to early June, timely pruning of the young shoots of golden privet can prevent adults from laying eggs on the unexpanded young leaves at the tips of the young shoots and kill newly hatched larvae, preventing a major outbreak of this pest.