Symptoms and Control Methods of Botrytis Blight in Primroses

Botrytis blight is a common and widespread disease of primroses.

[Pathogen] Botrytis cinerea Pers. et Fr.

[Symptoms] Water-soaked spots appear at leaf tips or leaf margins, then gradually enlarge, turn brown to black, and rot; stems develop irregular brown lesions and are prone to soft rot; flowers turn brown, rot, and drop off. In the late stage of the disease, a grayish-brown mold layer forms on the affected parts.

[Disease cycle] The pathogen overwinters in diseased plant residues or in the soil. Conidia are spread by wind and rain, entering through natural openings or wounds.

[Epidemic characteristics] Cold, rainy, and humid weather usually readily triggers botrytis blight epidemics. Excessive nitrogen or deficiency of potassium and calcium also tends to aggravate the occurrence of botrytis blight.

[Control measures] A. Planting density should be appropriate to facilitate ventilation, light penetration, and humidity reduction; avoid overhead irrigation when watering; control the amount of nitrogen fertilizer and increase the application of calcium and potassium fertilizers to improve plant resistance. B. Promptly remove diseased leaves and diseased plants; 70% quintozene powder at 8-9 grams per sq m can be mixed evenly with fine soil and then spread over the surface of potting soil or diseased soil for disinfection. C. In the early stage of the disease, spray 65% zineb wettable powder at 500-1000 times dilution or 50% procymidone wettable powder at 1000-1500 times dilution for control.