How to prevent and control garden balsam ring spot disease? A detailed guide to practical methods

Symptoms The disease occurs on leaves. Large round lesions with dark brown edges form. The surface of the lesions shows distinct concentric rings. In the later stage, the center of the lesion turns grayish brown, with scattered small black dots.

Pathogen: Ascochyta phaseolorum Saccardo, belonging to the genus Ascochyta, subphylum Deuteromycotina.

Transmission route: The pathogen overwinters and oversummers on diseased plant debris as pycnidia and perithecia. Conidia can spread via wind and rain. Conidia produced on later lesions continue to spread and cause secondary infections.

Control methods: In areas with severe disease year after year, begin spraying at the early stage of disease onset, spraying once every 7-10 days for 2-3 consecutive sprays. Commonly used pesticides include: 50% thiram wettable powder at 800 times dilution; 65% zineb wettable powder or 75% chlorothalonil wettable powder at 600 times dilution; 50% carbendazim wettable powder at 1000 times dilution, etc.