Black Spot Disease: Symptom Identification and Detailed Control Methods

Symptoms Leaves, petioles, young shoots and pedicels can all be affected, but the main damage is to the leaves. There are two types of symptoms: one is that in the early stage of the disease, small reddish-brown to purplish-brown spots appear on the leaf surface, gradually expanding into round or irregular dark black lesions, often surrounded by a yellow halo, with radiate edges, and the lesion diameter is about 3-15 mm. In the later stage, small black granules are scattered on the lesions, namely the pathogen's acervuli. In severe cases, the lower leaves of the plant turn yellow and wither, leaves fall early, and individual branches die, as in rose black spot disease. The other is the appearance on the leaves of brown to dark brown nearly round or irregular concentric ring spots, on which black mold-like material grows, namely the pathogen's conidia. In severe cases, the leaves fall early, affecting growth, as in elm-leaved spirea black spot disease. Disease pattern Black spot disease is the main disease on roses, occurring commonly and causing severe damage. The pathogen overwinters as mycelium or acervuli in dead branches or soil. In the following year, infection and disease onset begin in mid-to-late May, and July-September is the peak period of the disease. Conidia are spread by wind, rain or insects, expanding and causing secondary infection. Rainwater is the main condition for the epidemic of the disease; in years with early and abundant rainfall, the disease occurs earlier and more severely. Low-lying waterlogged areas, poor ventilation, insufficient light, and improper fertilization and watering are conducive to the disease. Control methods ① Select excellent disease-resistant varieties. ② After autumn, remove dead branches and fallen leaves, and burn them promptly. ③ Strengthencultivationmanagement, pay attention to shaping and pruning, and ensure ventilation and light penetration. ④ When new leaves unfold, spray 50% carbendazim wettable powder at 500-1000 times dilution, or 75% chlorothalonil at 500 times dilution, or 80% zineb at 500 times dilution, once every 7-10 days, for 3-4 consecutive sprays.