Identification and Control Methods of Poplar Black Spot Disease Explained in Detail
Poplar black spot disease, also known as poplar brown spot disease, is caused by a pathogen that can infect many species of poplar. Seedlings, young trees and mature trees can all be affected. When the disease is severe, it affects the normal growth of the trees and causes economic losses. Symptoms: it generally occurs on young leaves, shoot tips and fruit clusters, spreading from top to bottom, mainly damaging leaves. When the disease starts...
Poplar black spot disease, also known as poplar brown spot disease, is caused by a pathogen that can infect many species of poplar. Seedlings, young trees and mature trees can all be affected. When the disease is severe, it affects the normal growth of the trees and causes economic losses.
Symptoms: it generally occurs on young leaves, shoot tips and fruit clusters, spreading from top to bottom, mainly damaging leaves. At the early stage of the disease, needle-like, sunken, shiny small spots first appear on the underside of the leaves; afterwards the lesions enlarge to about 1 mm, are black and slightly raised, and brown spots also appear on the upper surface of the leaves. After 5 to 6 days, milky white raised small spots appear in the center of the lesions (on both the upper and lower surfaces of the leaves), namely the conidial stromata of the pathogen. Afterwards the lesions enlarge and merge into large spots, mostly round. When the disease is severe, the entire leaf turns black, and diseased leaves may fall prematurely by 2 months. When seedlings are young and tender, if all the leaves wither and die, the plants are easily killed. If small seedlings are affected when they emerge from the soil, the small leaves and the seedling collar all turn black, and the diseased seedlings become twisted and crooked.
Disease pattern: the pathogen overwinters as mycelium in the lesions of fallen leaves or twigs. The disease begins to occur in early May, is most severe in summer and autumn, and continues until leaf fall. It can damage poplar leaves, petioles, fruit clusters, young shoots and so on, forming angular, nearly round or irregular dark brown lesions on them, about 1 mm in diameter, some reaching 5 mm. When there are many lesions, they can merge into irregular large patches, causing early leaf fall. In May and June of the following year, the newly produced conidia of the pathogen are spread by wind and land on seedling leaves, invade the leaves through the stomata, symptoms appear in 3 to 4 days, and conidial acervuli form in 5 to 6 days, causing re-infection.
Comprehensive control methods: (1) Strengthen nursery management. Disease-resistant varieties should be selected for raising seedlings. Attention should be paid to timely thinning, improving ventilation and light conditions, and doing a good job of drainage and other field management to reduce conditions favorable for the disease. Continuous cropping should be avoided in nursery land, or the nursery should be kept away from infected plants, and crop rotation for seedling production can be carried out in a planned way. Seeds carrying the pathogen need chemical treatment to prevent the disease in seedling-grown plants; 85% chlorothalonil wettable powder at 1000 to 1500 times dilution, or thiophanate-methyl and dodine can be used for dusting dry seeds. (2) Plant at a reasonable density and thin in time to maintain ventilation and light penetration in the stand. Sweep up fallen leaves in the stand in time to reduce sources of the pathogen. (3) During the disease period, spray nurseries and established stands with 200 times Bordeaux mixture or 85% mancozeb at 250 times dilution. When spraying in the rainy season, 0.3% gelatin (or bean flour juice, soybean milk) should be added to the spray liquid to prevent it from being washed off by water, and diseased leaves and fallen leaves should be swept up and disposed of at any time to eliminate the pathogen. Alternatively, in early June, spray 40% carbendazim at 800 times dilution, or 25% chlorothalonil at 600 to 800 times dilution, or a mixture of 0.3% urea and potassium dihydrogen phosphate for control.