First, the symptoms
The young trunks of yellow skin trees are most susceptible to infection, typically within 10 to 15 centimeters from the ground. The affected area appears pale brown to grayish, slightly sunken, with the bark breaking and oozing yellow-brown mucous exudates. The xylem becomes discolored, turning brown, and shows visible circular necrosis lines that cross the base of the trunk. In the later stages, small black spots appear beneath the broken bark—these are the fruiting bodies of the pathogen. Leaves can also be affected, displaying gray-brown, round or irregularly shaped lesions. Infected leaves turn yellow, develop transparent veins, wilt, and in severe cases, may dry out and rot completely.Second, the pathogen
The causative agent of yellow skin disease is *Phomopsis wampi* (CF Zhang et PK Chi), a species belonging to the subgenus of Deuteromycotina. The fruiting bodies and their conidia are embedded beneath the bark, appearing dark brown. Within the fruiting bodies, two types of conidia are produced: Type A conidia are colorless, single-celled, straight or slightly curved, and oblong in shape; Type B conidia are also colorless but have a hooked structure. This pathogen specifically targets yellow skin trees and does not infect citrus or mango trees.Third, the infection cycle and disease conditions
The pathogen overwinters beneath the broken bark of infected trees. In spring, the pathogens produce a large number of conidia, which are spread by rain or wind. The pathogen has relatively low virulence and typically infects weakened trees or those with wounds. Once the pathogen reaches the trunk, it invades through these entry points. Excessive rainfall in spring creates favorable conditions for disease development. The disease is most active between April and May each year. If left unchecked, gummy disease can cause serious damage to the tree’s health and productivity.Fourth, control methods
Effective management requires a combination of cultural practices and treatment. After harvest, it's important to improve soil quality by tilling and adding organic fertilizers to enhance tree vigor. In early spring, regular inspections should be conducted on all trees. As soon as any signs of exudate are detected, immediate action must be taken. The recommended treatment involves scraping away the diseased tissue with a knife, followed by applying a mixture such as 1:1:10 Bordeaux paste, or diluting 50% carbendazim wettable powder at 100–200 times, or 50% Topozin wettable powder at 100 times. These treatments have proven effective in controlling the disease and promoting recovery.Overall, timely detection and proper care are essential in managing this disease. By maintaining strong tree health and implementing preventive measures, farmers can significantly reduce the impact of yellow skin disease on their crops.
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