Recently, there are fans and friends who have consulted more about the disease of large-leaf boxwood, and today I share the large-leaf boxwood leaf spot disease for everyone. Also known as large-leaf boxwood brown spot disease, mainly distributed in Tianjin, Beijing, Hebei, Shanghai, Guangdong, Hunan and other places, when harming large-leaved boxwood, causing large-leaf boxwood to fall leaves in advance, forming bald branches, resulting in plant death.
1, Symptoms
For the young leaves and old leaves of the large-leaved boxwood, at the beginning of the disease, there are small yellow spots on the leaves, which gradually become yellow-brown spots, expand into nearly round or irregular shapes, diameter 4 to 10 mm, the central gray-white, there are light brown concentric wheels, the edges are dark brown slightly raised, and the disease spots are densely covered with small black mold spots. The lesions pass through the back, but the back is slightly lighter than the front. The plaque withers and cracks until a perforation is formed. In severe cases, the disease spots are connected into one piece, and the leaves are yellow and fall off.
2. Pathogen
Fungus, Hemime Phylogenesporosporus cercospora destructiva rav. Conidia are whip-shaped or linear, straight or slightly curved, colorless, polyspores. The conidia are knee-like, dark, clustered on the ovary tissue, and the ovary is well developed, semicircular to subspherical.
3. Pathogenesis
Pathogens overwinter on diseased leaves or deciduous leaves in the form of mycelium or ovary, produce conidia in the spring for initial infestation, and then produce a large number of conidia throughout the growing season for multiple re-infections. When it is rainy, wet, frost damaged in spring, or plants are too dense and poorly ventilated, the disease is often severe, resulting in leaf fall. Generally, the infection begins in June, and the infection is the peak period from July to August, and symptoms appear in mid-August, and the onset of disease is severe from mid-to-late August to September, with enlarged spots and deciduous leaves. The severity of the disease is directly related to the temperature and the amount of rainfall, and the incidence is serious in generally high temperature and rainy and wet years.
Large-leaved boxwood leaf spot disease is easy to occur with mesophyllum, aphids, etc., which aggravates the disease of the plant. It is easy to cause diseases when the management is extensive, the drainage is not smooth, the planting is too dense, and the ventilation is poor.
4. Prevention and control methods
(1) Eliminate the source of infection: remove the diseased leaves in winter, burn or bury deeply, and eliminate the source of infection.
(2) When planting and raising seedlings, select robust plants to improve disease resistance.
(3) Spray 3 to 5be (Baume degree) stone sulfur compound in spring to eliminate the source of overwintering disease.
(4) Strengthen maintenance management: choose plots with good drainage and moderate fertility to facilitate plant growth, enhance tree potential, and improve disease resistance. Reasonable dense planting, pay attention to ventilation and light transmission, reduce foliar humidity, reduce morbidity. Watering should be appropriate, and drained in time on continuous rainy days.
(5) Chemical control: the initial stage of pathogenic bacteria infection is the best period for prevention and control, at this time, the drug control of large-leaved boxwood can be well controlled for the further development of the disease. Common chemical agents are 70% methyl tolbuzin wettable powder 1000 liquid, or 50% carbendazim wettable powder, or 75% Bacillus Clear wettable powder 500 times liquid, or 65% Daisen zinc wettable powder 600 to 800 times liquid. Chemical agents should be used alternately, sprayed every 7 to 10 days, the effect is good for 2 to 3 times in a row, and the best use can be combined with foliar fertilizer when spraying.
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