Causes, Symptoms and Control Methods of Persimmon Angular Leaf Spot

A very troublesome disease that harms persimmon trees is——persimmon angular leaf spot. It often gives growers a real headache. So how does persimmon angular leaf spot occur? What are the symptoms? How should it be controlled? Below, the editor of Tuliu.com takes you through it.

1. Symptoms

It mainly harms the calyxes and leaves of persimmon trees and Date Plum (Diospyros lotus). After the leaves are infected, yellowish-green lesions initially appear on the upper surface of the leaves, irregular in shape, with relatively blurred edges, and the veins within the lesions turn black. As the lesions expand, the color gradually deepens to light black, and afterward the color in the middle fades to light brown. Because the expansion of the lesions is restricted by the veins, the shape becomes angular, densely covered with small black velvety granules, with an obvious black edge. The underside of the lesions is initially light yellow, then the color gradually deepens, finally becoming brown or dark brown, also with a black edge, but less obvious than on the upper surface, and the small black granules are also sparser than on the upper surface. When the calyx is infected, the four corners are affected first, showing light yellow to dark brown lesions, angular in shape, then expanding inward, with edges black or not obvious; small black velvety granules are produced on both sides of the lesions, more on the underside of the leaf than on the upper surface.

2. Pathogen and Infection Route

The pathogen belongs to the fungal class Deuteromycotina, Hyphomycetes, Moniliales, Cercospora. The main infection route is that conidia invade through stomata via wind and rain for spread. The diseased calyxes remaining on the tree are the main source of infection and the site of spread. Generally, diseased calyxes can remain on the tree for 2-3 years, and the pathogen can survive in the diseased calyxes for more than 3 years. The angular leaf spot pathogen overwinters as mycelium in diseased calyxes and diseased leaves, with the diseased persimmon calyxes remaining on the tree as the main primary infection source and center of spread. In the rainy months of June and July of the following year, a large number of conidia can be produced on the diseased calyxes overwintering on the tree; the conidia invade through stomata with the help of wind and rain, with an incubation period of 25-38d, and the disease begins in early August. The optimum temperature for pathogen development is around 30°C. When the disease is severe in September, it can cause a large amount of leaf drop and fruit drop. The conidia formed on the lesions of the current year can carry out secondary infection when conditions are suitable. The timing of disease occurrence and the degree of damage are closely related to the timing and amount of rainfall in the rainy season of that year. For example, if rainfall comes early, with many rainy days and large rainfall amounts from May to August, it is conducive to the production and infection of conidia, and the disease occurs early and causes severe damage. Poor soil, weak tree vigor, and poor disease resistance lead to severe disease. Leaves in the inner part of the canopy, especially old leaves, are more severely affected. Trees near Date Plum are more severely affected. When there is heavy fog and the fog lasts a long time, the disease is also more severe.

3. Control Methods

1. Remove the diseased calyxes hanging on the persimmon trees. This is the main measure to reduce the source of the pathogen. Thoroughly removing the persimmon calyxes and eliminating the infection source can effectively control or reduce the occurrence of the disease.

2. Spray for protection. The critical period for preventive spraying is 20-30d after the persimmon tree flowers fall. The agents can be 1:3-5:200-300 Bordeaux mixture, 65% zineb wettable powder 500-600 times liquid, or 70% thiophanate-methyl 800-1000 times liquid, sprayed 2-3 times, which can effectively prevent the occurrence of the disease

3. Avoid mixed planting of persimmon trees and Date Plum. Date Plum has especially many calyxes and is infected by many pathogens. To avoid its carrying disease and infecting persimmon trees, mixed planting of persimmon trees and Date Plum should be avoided as much as possible.

4. Strengthen cultivation management. Apply more organic fertilizer, improve the disease resistance of the tree, reduce orchard humidity, create conditions unfavorable to pathogen reproduction, and control the occurrence of the disease.

5. Choose the site according to local conditions. Try to plant persimmon trees in well-ventilated, sunny places; low-lying and damp places are not suitable for developing persimmon trees. For the planting form, north-south rows in rectangular planting are preferable