Causes and Control Methods of Angular Leaf Spot in Cucumber, Watermelon, Melon and Mango

Angular leaf spot refers to a type of disease that occurs on the leaves of various crops such as cucumber, watermelon, melon and mango, with lesions shaped as polygons. So what are their causes and control methods? This disease is mainly prevented, and scientific management together with good ventilation and drainage conditions can greatly reduce the occurrence of the disease.

I. Causes and control methods of angular leaf spot in cucumber

1. Causes:

The pathogen invades through the stomata and wounds of leaves and fruits to cause disease, and is often splashed up by rainwater and spread around.

2. Control methods:

Agricultural control: plants are prone to the disease when fertilizer is insufficient and when they are aging. Seeds must be disinfected, and diseased leaves and diseased plants should be removed promptly and burned.

2. Chemical control:

Commonly used agents include 5% DT (copper succinate-glutarate) 500-fold solution, 72% agricultural streptomycin 4000-fold solution, 77% Kocide 1200-fold solution, or 75% Daconil 50 g plus 72% agricultural streptomycin 15 g mixed with 15 kg of water for spraying. The above agents can be used alternately, spraying once every 4 to 5 days for 3 to 4 consecutive sprays, and the control effect can reach more than 90%.

II. Causes and control methods of angular leaf spot in watermelon

1. Causes:

The pathogen mainly overwinters in the soil as mycelium or sclerotium-like bodies along with diseased plant residues, and the mycelium can also overwinter attached to seeds. When conditions are suitable, the mycelium directly invades the cotyledons and causes disease; in most cases the pathogen produces a large number of conidia that spread through rain or irrigation water, forming primary infection. After the disease occurs, the diseased parts produce conidia for repeated infection. The suitable temperature for the disease is 22—27℃, and the suitable humidity is 85%-98%.

2. Control methods:

(1) Seed collection from disease-free melons and seed treatment: before sowing, soak the seeds in 40% solution, or soak them in warm water at 55℃ for 15 minutes, wash them clean with water, then germinate and sow.

(2) During the growing period or after harvest, remove diseased leaves and diseased plants and bury them deeply, and carry out deep plowing.

III. Causes and control methods of angular leaf spot in melon

1. Causes:

A disease caused by bacteria; the pathogen overwinters in the soil along with diseased plant residues or attached to the seed surface, invades through the wounds and natural openings of the host, and spreads through wind and rain, insects and human contact. Damp and rainy conditions and high humidity in the field are the main conditions for the occurrence of the disease.

2. Control methods:

(1) Carry out crop rotation with non-Cucurbitaceae crops for more than 2 years.

(2) Select disease-free melons for seed saving, and disinfect the seeds before sowing. The disinfection method is to soak the seeds in warm water at 55℃ for 20 minutes, or soak them in 0.1% mercuric chloride solution + “Yunda-120” 1500-fold for 10 minutes, or soak them in calcium hypochlorite 300-fold solution + “Yunda-120” 1500-fold for 30—60 minutes, then remove them and wash them clean with water, or soak them in streptomycin sulfate or new phytomycin + “Yunda-120” 500-fold for 2 hours, then remove them, germinate and sow.

(3) Promptly remove diseased leaves and diseased vines and bury them deeply; topdress fertilizer in time and water reasonably, and for greenhouse melons strengthen ventilation and dehumidification management.

IV. Causes and control methods of angular leaf spot in mango

1. Causes:

(1) Angular leaf spot is a bacterial disease.

(2) Diseased leaves, diseased branches, diseased fruits, diseased plant residues, diseased seedlings and host weeds in or around the orchard are the primary infection sources of bacterial angular leaf spot in mango.

(3) The pathogen can spread and diffuse through airflow, diseased seedlings, wind and rainwater. The pathogen invades through wounds and natural openings such as water pores of leaves and fruits and causes disease.

(4) The optimum temperature for the development of the pathogen is 20 to 25℃. High temperature and heavy rain favor the occurrence of this disease. Usually areas with strong wind, windward zones or low-lying orchards have more severe disease, while wind-sheltered orchards on higher terrain have milder disease. At present, the main mango varieties differ somewhat in their resistance to bacterial angular leaf spot, but there are no immune varieties.

2. Control methods:

(1) Do a good job of orchard cleaning: half a month before bud break, and after fruit harvest in autumn and after 2/3 of the leaves have fallen, spray the whole orchard with 60-100-fold Kuifuling solution to kill the pathogen and nourish the tree.

(2) Spray regularly during the growing period: spray 300-500-fold Liangguoan + 600-fold Wofengsu for protective spraying, especially at the leaf expansion stage, spray 300-fold Liangguoan and 600-fold Wofengsu twice.