How to effectively prevent and control common pests and diseases of Euonymus japonicus?
Euonymus japonicus, as an evergreen shrub, is one of the most commonly used landscaping plants in urban streets, squares, parks, institutional courtyards, and residential green spaces. Due to the large differences in its growing environment and relatively extensive management measures, the occurrence and damage of its pests and diseases are also relatively severe, seriously affecting the urban landscaping landscape. Investigating and studying the occurrence characteristics of the main pests and diseases of Euonymus japonicus can help formulate and implement prevention and control measures according to local conditions, achieving the goal of controlling damage and beautifying the environment.
1. Occurrence characteristics of main pests and diseases
(1) Euonymus japonicus powdery mildew. Powdery mildew is a common disease in Euonymus japonicus seedlings and green belts, mainly occurring on the upper surface of leaves, and occasionally on the underside. The lesions are round and white, with a radial pattern around the edges. In severe cases, small lesions merge into large white powdery patches with unclear edges. When the white powdery layer is wiped off, yellow spots can be seen. It causes leaf shrinkage, slight distortion of diseased shoots, and premature leaf drop.
The pathogen of powdery mildew is a fungus, which can also harm other Euonymus species. The pathogen overwinters as mycelium and fruiting bodies on diseased plants or diseased residues. In May of the following year, conidia can be produced and spread by wind and rain. During the growing season of Euonymus, the fungus can infect multiple times. High temperature and high humidity in June and July, and over-dense planting are conducive to disease development. In August, when the temperature is above 30 degrees Celsius, the disease decreases, and in autumn, a small peak of disease occurrence appears again.
(2) Euonymus japonicus anthracnose. In the early stage of the disease, water-soaked yellowish-brown small spots appear on the leaves, with unclear boundaries between diseased and healthy tissue. Later, the lesions expand, and in the later stage, the diseased areas turn yellow, with small black spots (conidia acervuli) appearing on the lesions, arranged in obvious or indistinct concentric rings, often causing leaf blight and premature leaf drop. The pathogen of anthracnose is a fungus, which overwinters as conidia acervuli in diseased residues and soil, and can also overwinter as conidia and mycelium on diseased plant tissues. In late spring of the following year, conidia spread by insects, wind, and rain. Conidia invade through stomata or wounds. During the growing season of Euonymus, it can be infected repeatedly, with the most severe occurrence in summer and autumn each year. Generally, the disease worsens when there are many wounds on the plant, the plants are too dense, ventilation is poor, nitrogen fertilizer is applied excessively, and the plants grow weakly.
(3) Ceroplastes japonicus. It belongs to the order Homoptera, family Coccidae. In addition to harming Euonymus japonicus, it can also harm more than 150 other woody flowering plants and fruit trees; it has a very mixed diet and strong reproductive capacity. When the damage is severe, the new shoots and leaf undersides of the host are covered with insects, often causing sooty mold, leading to plant weakening and even death.
This insect has 1 generation per year, overwintering as fertilized female adults on branches. In May of the following year, they begin to lay eggs, with mid-to-late June being the peak egg-laying period. Eggs are laid inside the scale shell, and each female adult can lay about 1000 eggs on average. The egg stage lasts about 20 days. From late June to mid-July is the peak hatching period of nymphs. Newly hatched nymphs crawl onto leaves to cause damage, fix themselves and suck sap, then secrete waxy substances, gradually forming star-shaped scale shells. After more than 1 month of damage, the waxy scale shells of male and female nymphs change significantly. Male nymphs at the 2nd instar emerge as male adults in early September and die after mating; female nymphs at the 3rd instar gradually migrate from leaves to branches to cause damage with each molt, and after fertilization, begin to overwinter in late October.
(4) Two-spotted spider mite. It belongs to the order Trombidiformes, family Tetranychidae. It can harm more than 100 species of flowers, trees, fruit trees, and crops. It damages leaves by sucking, causing chlorotic yellow spots on leaves, making leaves dull and causing premature drop.
In northern regions, about 10 generations occur each year. It overwinters as fertilized female adults in soil crevices, bark crevices, and other places, and begins to reproduce in spring of the following year. It mainly reproduces sexually, but when male adults are lacking, it can also reproduce by parthenogenesis, and all offspring are male. Each female mite can lay more than 100 eggs on average. In July and August, when temperatures are high and drought with little rain occurs, it reproduces rapidly, causing rampant damage and easily leading to disasters. This mite has the habit of spinning silk webs, often resting under silk webs near the main vein on the underside of leaves. It enters overwintering in October.
2. Integrated control methods. As long as timely prevention is carried out according to the occurrence patterns of the above pests and diseases, their damage can be significantly reduced, and can even be effectively avoided.
(1) Eliminate insect and pathogen sources. Combined with shaping and pruning, remove dead branches, diseased and disabled branches, and insect-infested branches, and burn them in a centralized manner to reduce pathogen and insect sources.
(2) Strengthen management. Seedling raising and landscaping planting should not be too dense, and ventilation and light conditions should be improved; during management operations, try to avoid causing wounds on plants; do not apply excessive nitrogen fertilizer, and increase the application of phosphorus and potassium fertilizers. Create conditions unfavorable for disease infection and improve the plant's ability to resist diseases and pests.
(3) Chemical pesticide control. Carry out at the early stage of disease occurrence and the early occurrence stage of young pests. For powdery mildew, spray with 20% triadimefon emulsifiable concentrate at 2000 times dilution; for anthracnose, spray with 80% carbendazim-thiram wettable powder at 500-800 times dilution; for Ceroplastes japonicus, spray with 40% omethoate emulsifiable concentrate at 1000 times dilution or 50% malathion emulsifiable concentrate at 600-800 times dilution; for two-spotted spider mite, spray with 1.8% abamectin or 15% saomanjing emulsifiable concentrate at 3000 times dilution. If multiple pests and diseases occur together, the above agents can be mixed and sprayed for simultaneous control.