Detailed Explanation of Pest and Disease Control Techniques for Euonymus japonicus
Euonymus japonicus is currently an excellent evergreen broadleaf tree species for urban landscaping and ecological environment improvement in northern China, with more than 1 billion plants planted. Its stress resistance and ornamental value are outstanding, and it can maintain glossy green foliage in winter. It is mainly planted as hedges, large color-block topiary and specimen plants.
In recent years, because quarantine and treatment of pests and diseases have been neglected in the interregional exchange of nursery stock, the area affected by pests and diseases has expanded year by year, and some pests and diseases have become disasters due to delayed control, affecting growth vigor and ornamental value in mild cases and causing plant death in severe cases. During cultivation, the common pests and diseases include the following:
1. Euonymus japonicus powdery mildew. It mainly damages the leaves of Euonymus japonicus, and when severe, it can also infect new shoots. The pathogen produces a gray membranous fungal layer in late autumn and winter to overwinter. In early April of the following year, when the temperature is above 18°C and the relative air humidity is 70-85%, that is, during the leaf expansion period of new shoots of Euonymus japonicus, the pathogen on old leaves produces a large number of conidia, which spread by wind to new leaves and germinate on them, producing germ tubes and finally invading the tissues. Newly infected leaves first fade green and develop yellow spots, then many small round spots are scattered on the leaves. As the disease worsens, the lesions gradually expand and merge with each other, becoming irregular large spots. Because this fungus parasitizes the surface of the host branches and leaves and produces haustoria that penetrate deep into epidermal cells to absorb nutrients, after new leaves are infected, they often show symptoms of wilting and water loss, the leaves become thinner and wrinkled, and the diseased shoots are distorted and shrunken
Control methods: (1) Prune appropriately to enhance air permeability. (2) In the early stage of the disease, alternately spray 25% triadimefon 1300 times dilution, 70% thiophanate-methyl 700 times dilution, and 50% Tuzet wettable powder 800 times dilution. If the disease is severe, pruning must be carried out, and the diseased leaves should be cut off and burned centrally, then fungicides should be sprayed for control.
2. Euonymus japonicus brown spot. It overwinters in the lesion area as mycelium and stroma. In late May each year, when the temperature rises to about 25°C, the stroma in old lesions produces conidia and begins primary infection. It generally infects the lower old leaves first. After old leaves are infected, brownish-green small spots initially appear on the leaves, gradually turn yellow and then brown. The lesions are nearly round or irregular and can connect into patches, with a grayish-white center and a slightly raised light brown ring at the edge, and densely covered with small black dots. Once conditions are suitable, reinfection continues. Early June to mid-July is the peak period of disease expansion, and after October it enters the dormant period.
Control methods: (1) Select healthy disease-free nursery stock for planting. (2) From early June to July, spray 50% carbendazim 500 times dilution or 75% chlorothalonil 500 times dilution, or 50% Tuzet wettable powder 800-1000 times dilution for prevention to reduce the incidence rate, spraying once every 10-15 days for 3 consecutive sprays. (3) In winter, remove fallen leaves and burn them centrally.
3. Aphids. Wingless parthenogenetic female aphids and nymphs gather on branch tips and the undersides of young leaves to suck sap and cause damage. The damaged leaves often have white waxy secretions, which easily cause sooty mold, and in severe cases the branches and leaves turn black, affecting plant growth and ornamental value. Generally, about 10 generations occur per year.
Control methods: (1) Protect natural enemies such as ladybugs and green lacewings. (2) Chemical control: 20% fenvalerate-malathion emulsifiable concentrate 2000 times dilution or 2000-3000 times imidacloprid powder can be sprayed.
4. Japanese wax scale. One generation occurs per year, overwintering as fertilized adult females on branches and trunks, with the peak hatching period from mid-June to early July.
Morphological characteristics: adult female, wax shell grayish-white or slightly flesh-red, oval. Adult male, body dark brown or brown, head and thoracic dorsal plate darker. Nymph, wax shell ovate to elliptical, with a slightly raised back.
Control methods: (1) Quarantine measures. When purchasing seedlings from other places, plant quarantine procedures must be strictly implemented to prevent artificial spread of pests. (2) Strengthen garden maintenance and management. Through maintenance and management, create environmental conditions unsuitable for scale insects. Practice crop rotation, clean the garden in time, and burn fallen leaves, weeds, and diseased and pest-infested branches centrally to reduce the overwintering pest population base. Fertilize reasonably to enhance plant resistance. Prune reasonably to increase ventilation and light penetration, change the living environment of scale insects, weaken their reproductive capacity, and reduce damage. (3) Chemical control. When the pest population density is not high, a soft brush dipped in a small amount of dichlorvos diluted with water (1:50-100 times dilution) can be used to wipe them out, or the damaged branches can be removed and burned centrally. During the peak occurrence period of nymphs, spray 40% omethoate 1000 times dilution or deltamethrin 2500 times dilution, once every 10 days or so for 3 consecutive sprays. (4) Protect natural enemies such as parasitic wasps.
5. Euonymus japonicus geometrid moth. Three generations occur per year, overwintering as pupae in the litter layer of dead branches and fallen leaves on the soil surface. Adults of the overwintering generation begin to emerge in early April, with the peak emergence in mid-April. They lay eggs 1-2 days after emergence, with the peak egg-laying period in mid-April, and the egg stage lasts 6-7 days. First-generation larvae cause damage from late April to mid-May, second-generation larvae appear from mid-June to early July, and the third generation from early August to early October. A few larvae enter the soil to overwinter in early September. During the year, damage is most severe from late April to mid-May and in late August. After hatching, the larvae gather on the undersides of host leaves within 3-4 hours and feed on the leaf mesophyll, and after the third instar they disperse to feed on leaves. When the pest population density is high, there can be as many as 30-50 larvae on a single tree. When food is scarce, the petioles and cortex of new shoots are also gnawed, seriously affecting tree growth and even causing tree death.
Control methods: (1) Use the phototaxis of adults to carry out light trapping and killing during the adult stage. (2) During the larval damage period, spray 50% fenitrothion emulsifiable concentrate 500 times dilution or 4.5% beta-cypermethrin 2000 times dilution. (3) Remove egg masses during the egg-laying period. In winter, plow and turn the soil around the roots to kill overwintering pupae.