What are the control methods for scale insects on privet hedges?
In recent years, with the widespread use of golden privet (Ligustrum sinense 'Variegatum') and small-leaf privet (Ligustrum quihoui) in urban landscaping, pests and diseases on privet have become a major problem in garden maintenance and management. The scale insect occurring on Ligustrum landscaping plants is mainly the white wax scale (Ericerus pela). It has been reported that comstock mealybug (Pseudococcus comstocki) has occurred on privet hedges in Hebei. The identification characteristics and control measures of the white wax scale are described below:
Distribution and damage
The white wax scale Ericerus pela (Chavannes) belongs to the order Homoptera, family Coccidae. It is widely distributed in China. It damages large-leaf privet (Ligustrum lucidum), privet (Ligustrum japonicum), Japanese privet (Ligustrum japonicum), small-leaf ash (Fraxinus bungeana), American ash (Fraxinus americana), water ash (Fraxinus mandshurica), deodar cedar (Cedrus deodara), citrus, camellia and pomelo, etc.
The comstock mealybug (Pseudococcus comstocki Kuwana), also called mulberry mealybug, pear mealybug, or plum mealybug, belongs to the family Pseudococcidae. It mainly damages kumquat, black locust (Robinia pseudoacacia), camphor tree (Cinnamomum camphora), chayote, apple, pear, peach, plum, apricot, hawthorn, grape, clivia (Clivia miniata), Euphorbia neriifolia, dracaena (Dracaena sanderiana), ivy (Hedera helix), jasmine, sugar maple, etc.
Damage symptoms: Both pests use adults and nymphs to pierce and suck on host branches, causing tree vigor to decline, growth to slow, and even branches to die.
Morphological characteristics
Identification characteristics of the white wax scale: Before fertilization, the female adult has a raised back, mussel-shell shaped; after fertilization, it expands into a hemispherical shape, about 10 mm long and about 7 mm high. It is yellow-brown, light red to reddish-brown, scattered with light black spots, and the abdomen is yellow-green. The male adult is about 2 mm long, yellow-brown, with transparent wings that have an iridescent sheen, and two white wax filaments at the tail. Eggs: female eggs are reddish-brown, male eggs are light yellow. Nymphs are yellow-brown and oval.
Identification characteristics of the comstock mealybug: Adult. The female adult is oval, relatively flat, 3-5 mm long, pink, covered with white wax powder, with 17 pairs of white wax spines along the body margin, and the pair at the end of the abdomen is almost equal to the body length. Antennae mostly 8-segmented. One ventral fissure, relatively large, oval. The anal ring has 6 anal ring setae. The anal lobes are well developed, with 1 anal lobe seta and several long hairs at the tip. Multilocular pores are distributed on both the dorsal and ventral surfaces of the body. There are 17 pairs of cerarii, and body hairs are very numerous, distributed on both the dorsal and ventral surfaces; the body hairs along the dorsal midline and nearby are slightly longer. The male adult is purple-brown, about 1 mm long, with a wingspan of about 2 mm, with 1 pair of transparent wings. Eggs are oval, light orange-yellow, and the ovisac is white and flocculent. Nymphs are oval, flat, and light yellow. The pupa is light purple, 1.2 mm long.
Lifestyle habits
The white wax scale has 1 generation per year and overwinters as fertilized female adults on branches. In March of the following year, the female adult body swells with eggs, and egg laying begins in early April; the egg stage is about 7 days. In the Shanghai area, the nymph stage of the white wax scale coincides with the flowering period of small-leaf privet. Newly hatched nymphs parasitize on leaves near the mother body, and after the 2nd instar they move to branches to cause damage. After settling, male nymphs secrete a large amount of white waxy material, covering the body and branches; in severe cases, the entire branch appears as a white rod. In early October, male adults emerge, mate, and then die. The fertilized female adult gradually grows larger and, as the temperature drops, overwinters successively. According to reports, in the Dalian area, late June is the peak hatching period for nymphs; in the Kunming area, there is no overwintering phenomenon, and nymphs begin hatching in mid-March. Continuous high temperature and drought or continuous rainy weather can cause massive death of nymphs.
The comstock mealybug generally has 3 generations per year and overwinters as ovisacs in crevices of tree trunks and branches, etc. The peak hatching periods of nymphs for each generation are mid-to-late May, mid-to-late July, and late August. During the nymph developmental period, females take 35-50 days and males take 25-37 days. Male nymphs pupate in white elongated cocoons. Each female adult can lay 200-400 eggs, and ovisacs are mostly distributed in bark crevices, etc. On flowers and trees, adults and nymphs mostly gather on young buds and tender branches to cause damage.
Control measures: In the first year after planting a privet hedge, pests and diseases rarely occur. After the hedge takes shape in the second year, due to poor ventilation and light transmission, scale insects are very likely to occur.
1. Strengthen quarantine: Strictly implement the quarantine system, do not introduce infected seedlings. Do not take scions or cuttings from infected seedlings.
2. Scientific management: In winter, eliminate adults in combination with pruning to avoid a large occurrence of nymphs the following spring. Strengthen management, pay attention to ventilation, fertilize reasonably, water scientifically, and enhance tree vigor and disease resistance. During the growing season, try not to do heavy pruning. When pruning is necessary, after pruning spray a protective fungicide every 7 to 10 days, such as Hupingdan 300x solution or mancozeb 1500x or carbendazim 1000x, for 3 to 4 consecutive sprays.
3. Timely observation: Frequently inspect for pest activity, check whether white flocculent material appears, detect early, and control at the right time.
4. Protect natural enemies: Pay attention to protecting and utilizing the natural enemies of scale insects, such as parasitic wasps, predatory ladybugs, and green lacewings.
5. Chemical control: Chemical control is effective during the peak egg hatching period or the first-instar nymph stage. Use Kuangshajie 1000-1500x solution or Jiesha 1000x solution or Supracide 1000-1500x solution, spraying once every 5 to 7 days, for 2 to 3 consecutive applications, and they can all be eliminated.
When controlling adult scales, Kuangshajie 800-1000x solution can be used for uniform spraying.
When spraying, be sure to spray the whole plant (including diseased plants and healthy plants), and ensure the front and back of leaves are evenly covered with the solution; when there are few affected plants, a wet cotton ball soaked in machine oil or alcohol can be used to repeatedly wipe the damaged areas, which can completely kill the nymphs, with very good results.