How to deal with leaf spot disease on Euonymus japonicus? Detailed explanation of prevention and control methods
Euonymus japonicus is a commonly used evergreen small shrub grown for its foliage in landscaping, and it has many advantages, but the occurrence of leaf spot disease causes the plant to drop its leaves prematurely, resulting in bare branches and even death, seriously affecting the normal growth and ornamental effect of Euonymus japonicus.
Symptoms of leaf spot disease: In the early stage of the disease, there are small yellow spots on the leaves, which gradually turn yellowish-brown and expand into round or irregular spots. The diameter of the spots is 2 mm to 10 mm. In the later stage, the spots are grayish-brown or grayish-white with darker edges, and many small black dots grow on the spots. In severe cases, the spots join together into a single patch, and the leaves turn yellow and fall off.
Disease pattern: The pathogen overwinters in the form of mycelium and other structures on diseased leaves or fallen leaves, serving as the primary infection source. Spores are spread by wind and rain. In the spring of the following year, as the temperature rises, conidia are produced and invade through stomata, pruning cuts, or wounds. In the Tangshan area of Hebei, infection generally begins in June, with the peak infection period in July and August. Symptoms appear in mid-August, and the disease is severe from mid-to-late August to September, with spots expanding and leaf drop occurring. The severity of the disease is directly related to temperature and the amount of rainfall; generally, years with high temperatures, abundant rain, and humid, moldy conditions see severe disease. Leaf spot disease on Euonymus japonicus is prone to occurring together with scale insects, aphids, and other pests, worsening the plant's condition. When management is extensive, drainage is poor, planting is too dense, and ventilation is poor, the disease is likely to occur.
Prevention and control measures: Following the principle of "prevention first, combining prevention and control." Work hard on plant selection, planting, and management to enhance the plant's disease resistance. When disease occurs, treat it early, treat it when it is minor, and treat it thoroughly to inhibit its development.
1. Eliminate the infection source: In winter, clear away diseased fallen leaves, burn or bury them deeply, and eliminate the infection source.
2. When planting and raising seedlings, select robust plants to improve disease resistance.
3. Strengthen maintenance and management: Choose plots with good drainage and moderate fertility to facilitate plant growth, strengthen tree vigor, and improve disease resistance. Plant at a reasonable density, pay attention to ventilation and light transmission, reduce leaf surface humidity, and reduce the incidence of disease.
4. Chemical control: The early stage of pathogen infection is the best time for control. At this time, applying chemical treatment to Euonymus japonicus can effectively control further development of the disease. Common chemical agents include 1% Bordeaux mixture, 75% thiophanate at 1500 times dilution, 50% carbendazim, and 75% chlorothalonil at 500 times dilution. Chemical agents should be used alternately, sprayed once every 7 to 10 days, with 2 to 3 consecutive applications giving good results.