This image looks like Cladosporium. At the time, due to issues with the microscope, it could not be photographed clearly and could not be accurately identified. It is very likely a secondary parasite and not the main pathogen causing the disease and rot.

The following images are of related fungi not from bayberry, for reference.

Trichoderma viride Image source: Official plant protection database of CABI (Centre for Agriculture and Bioscience International)

A grayish-white mold layer appears on the surface of the fruit, causing the flesh to rot and the fruit surface to become sunken. After infection, the bayberry fruit becomes inedible. If not controlled in time, the lesions will expand rapidly, and within 48 hours, a large number of bayberry fruits can rot and fall to the ground.

Initial symptoms

Grayish-white mold layer

Massive fruit drop

The disease is severe under continuous rainfall at temperatures of 25-30°C. The high-incidence period is during the fruit ripening and harvesting stage of bayberry. This period coincides with midsummer, characterized by high temperature, frequent rain, and high humidity, creating a favorable environment for pathogen infection. Generally, the more rainfall and the higher the maturity of the bayberry, the more likely white rot disease is to outbreak. Especially during continuous rainy days, poor ventilation in the orchard and soaked branches and leaves of bayberry trees easily trigger large-scale pathogen reproduction. At the same time, after fruit ripening, acidity decreases and disease resistance weakens, making the fruit more susceptible to infection.

Agricultural Control

1. Orchard Cleaning

The white rot pathogen has strong survival ability and can overwinter in dead branches, fallen leaves, rotten fruits, and soil, becoming the primary infection source for the next year. Therefore, orchard cleaning after winter pruning can greatly reduce the initial pathogen base and alleviate the control pressure in the following year. The role of orchard cleaning must be emphasized; it is the most effective and worthwhile agricultural practice for disease prevention. If orchard cleaning is done well, it can reduce more than 90% of the initial pathogens, achieving twice the result with half the effort.

How to clean the orchard? After fruit picking and pruning, as well as after winter pruning, promptly remove the pruned diseased branches from the orchard and burn them. After winter pruning, spray the entire orchard with cleaning agents such as lime sulfur mixture and amobam to kill pests and diseases.

2. Pruning

Dwarf the tree to below 3 meters, prune for good ventilation and light penetration, and avoid dense and excessive vegetative growth, which can reduce the incidence of the disease.

3. Fertilization

For adult fruit-bearing trees, avoid excessive use of nitrogen and phosphorus fertilizers, as they can easily cause excessive vegetative growth and canopy closure, especially in the Dongkui variety. It is recommended to use organic fertilizers as the mainstay, supplemented with potassium sulfate and medium and trace element fertilizers. For weakened trees, use balanced compound fertilizers.

4. Chemical Control

White rot disease is caused by mixed infection of multiple pathogens. During the fruit ripening season, when it encounters the plum rain and high-temperature season, the disease is severe every year, and conventional pesticides may not be effective in some years. In particular, commonly used pesticides such as difenoconazole, imazalil, tebuconazole, and pyraclostrobin, when used year after year with increasing dosages, have developed varying degrees of resistance, and their effectiveness has become increasingly unsatisfactory. Moreover, products with the same active ingredient from different companies may also vary in efficacy, leaving fruit growers at a loss when selecting appropriate pesticides for control.

Therefore, it is necessary to choose ingredients that are new in composition, low in resistance, require small dosages, have good efficacy, are green and safe, and have good compatibility. For example, ingredients such as mefentrifluconazole, fluxapyroxad, pydiflumetofen, and fluopyram are currently among the most effective pesticides for controlling white rot disease in bayberry cultivation and can be used with confidence.