Symptoms: Leaves, petioles, twigs, and pedicels can all be affected, but they are mainly damaged leaves.

There are two types of symptoms: one is the appearance of reddish-brown to purple-brown dots on the surface of the leaves at the beginning of the disease, and gradually expands into round or amorphous dark black spots. There are often yellow halos around the lesions, and the edges are radial and sick. Spot diameter of about 3 to 15 mm. A small black spot was scattered on the later stage of the lesion, which was the spore plate of the pathogen. In severe cases, the lower leaves of the plants are brown and early leaves fall, causing individual branches to die, such as rose black spot.

The other is a brownish to dark brownish brownish-ringy or irregularly shaped lenticular vein on which black moldy species, the conidia of germs, are grown. In severe cases, the leaves fall early and affect growth, such as black spot disease of Prunus triloba.

Incidence of disease Black spot disease is the main disease on the Chinese rose. It occurs widely and is seriously endangered. The pathogens overwinter in dead branches or soil with mycelium or conidium discs. The onset of infestation began in the middle and late May of the following year, and the onset of disease occurred from July to September. Conidia spread by wind, rain, or insects, expand and infect.

Rainwater is the main condition for disease epidemics. In early years with heavy rainfall, the onset was early and heavy. Low-lying stagnant water, poor ventilation, lack of light, improper fertilizer and water, etc. are conducive to disease.

Control methods

1 Select excellent resistant varieties.

2 After the fall, remove dead branches, fallen leaves, and burned.

3 strengthen the cultivation and management, pay attention to pruning, ventilation and light transmission.

4 When the new leaf is unfolded, spray 50% carbendazim WP 500 to 1000 times, or 75% chlorothalonil 500 times, or 80% dexamethasone 500 times, 7 to 10 days, spray 3 to 4 times.

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