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Symptom Identification and Control Methods for Black Locust Trunk Rot

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Symptoms: The disease affects the branches and trunks of young trees to large trees, causing branch dieback or death of the entire tree. In large trees, it mainly occurs at the base of the trunk, and in a few cases at the forks of upper branches and tips. When the base of a large tree is affected, there are no obvious external symptoms; when the bark is peeled back, the interior has already discolored and rotted, with a foul odor, and irregular brown to dark brown patches appear on the surface of the xylem. The lesions continuously expand, encircling the trunk for 1 full turn, causing the branches and trunk above the lesion to die, and the leaves immediately turn yellow and wilt. When the branch tips or the main stem of young trees are affected, the diseased tissue shows water-soaked rot, producing obvious canker lesions that are slightly sunken with purplish-brown edges

Symptoms: The disease affects the branches and trunks of young trees to large trees, causing branch dieback or death of the entire tree. In large trees, it mainly occurs at the base of the trunk, and in a few cases at the forks of upper branches and tips. When the base of a large tree is affected, there are no obvious external symptoms; when the bark is peeled back, the interior has already discolored and rotted, with a foul odor, and irregular brown to dark brown patches appear on the surface of the xylem. The lesions continuously expand, encircling the trunk for 1 full turn, causing the branches and trunk above the lesion to die, and the leaves immediately turn yellow and wilt. When the branch tips or the main stem of young trees are affected, the diseased tissue shows water-soaked rot, producing obvious canker lesions that are slightly sunken with purplish-brown edges. As the lesions expand, the parts above the lesions soon die.

Pathogen: The pathogen is Phytophthora cinnamomi Rands, belonging to the phylum Mastigomycota, class Oomycetes, order Peronosporales.

Disease pattern: The pathogen often invades from the base of the trunk, though some cases develop from the trunk. Wounds caused by underground pests are the main route of infection. Wounds caused by excessively high soil moisture or strong winds, as well as mechanical injuries caused by human and livestock activity, can all serve as infection routes. The peak disease period is from May to September. When the temperature is above 25°C and the relative humidity is above 85%, the lesions expand rapidly.

Control: ① Low-lying waterlogged areas or sites near water sources are not suitable for planting black locust. Alternatively, dig drainage ditches to reduce soil moisture. ② Promptly remove dead trees or remnant stumps, and disinfect the soil with 5% formaldehyde solution. ③ Whitewashing the trunk and spreading copper sulfate, ferrous sulfate, or lime on the soil surface have some control effect. ④ For early lesions, use surgical excision to dig them out, or punch holes or make cuts with a knife on the lesions, then apply 25% carbendazim at 30-50 times dilution or 50% thiophanate at 60 times dilution, applying 2-3 times, which has an inhibitory effect on the disease. ⑤ Irrigate the soil with deltamethrin at 2000 times dilution to control underground pests.

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