Your photo is not close-up, so you can't tell the cause at a glance. However, it is initially suspected to be "walnut black spot disease", which belongs to bacterial infection, and it is easy to get sick when it is rainy and overgrown. Disease characteristics: at the initial stage, the leaves appear with yellow halo, and then the lesions are cut off by the veins of the leaves and become polygons; If it is serious, strip-shaped lesions will appear across the veins and petioles. If it is serious, brown waterlogged lesions will appear on the tender tips and the leaves will dry up and fall off. The symptomatic pesticide is "agricultural streptomycin", so pay attention to the use of drugs standardized by big manufacturers.

In addition, walnut disease should be mainly prevented, and it should be prevented in rainy weather. It is effective to spray with preventive pesticides such as Bordeaux mixture. Then there is to increase ventilation and light transmission, weed in time, and reserve ventilation and light transmission space for walnut trees.