1. Lemon scab: This is a fungal disease, which mainly harms new shoots, young leaves and young fruits. Oil spots will appear after the leaves are damaged, and the back of the leaves is funnel-shaped and the leaves are sunken. In severe cases, the treetops will be shortened and the leaves will be distorted. The symptom of fruit is the appearance of many tumor-like processes. The disease can be prevented by pruning regularly, removing diseased leaves and branches, and spraying 2-3 times each time when the new shoots are 1-2cm long and the flowers fall. Commonly used drugs are 600-800 times of 70% thiophanate or 600-800 times of 50% carbendazim.
2. Lemon soot disease: This is a fungal disease, which mainly harms leaves, branches and fruits. Dark brown mildew spots will appear on the surface of the injured part, and gradually expand the connection, forming a furry, film-like black mildew spot layer. The pathogen feeds on the dense dew secreted by scale insects, aphids and whiteflies. And then disappear on the surface of leaves for reproduction, which not only affects photosynthesis, but also secretes toxins to weaken the growth potential of plants and reduce fruit quality. The control methods include strengthening the control of scale insects, whiteflies, whiteflies and aphids, spraying corresponding chemicals to eliminate the transmission medium of soot disease, strengthening the management of lemon orchards, and reasonable pruning to facilitate ventilation and reduce the incidence factors.
To sum up, further observation and diagnosis are needed to determine specific diseases and take corresponding control measures.