How to identify tomato late blight

Late blight: the whole growth period and leaves, stems and fruits can be damaged, especially leaves and green fruits. The disease of seedlings generally appeared dark green watery spots from the leaves, and then extended to the stem, showing dark brown rot near the petiole. with the development of the disease, the base of the young stem was waterlogged constricted and the plant wilted and collapsed. In the adult stage, the disease began to develop upward from the lower leaves, from the leaf tip and leaf edge to produce dark green water-stained spots, gradually turned brown, and when the disease was serious, the whole plant leaves withered; the disease spots on the stem were brown or dark brown water stains, slightly sunken; fruit spots initially oily dark green, gradually changed to dark brown to brown, disease spots moire-like, rough hardening. White mildew layer can be produced in all the affected parts when it is moist. Precautions: 1. Sometimes the leaf disease spot is V-shaped from the leaf tip, or when the condition is not suitable, the disease part is dry, and there is no mildew layer, so it is easy to be confused with Botrytis cinerea when simple leaf disease occurs. 2. When the environmental conditions are especially suitable, the disease occurs rapidly, and there is no obvious disease spot in the leaves, but obvious white mildew appears. 3. Simple leaves are easy to be confused with frost injury, but frost injury occurs in the upper leaves. 4. Improper fertilization will also lead to the drying up of leaves similar to late blight, which begins from the lower leaves, but is evenly distributed in the whole field.