Symptom Identification and Control Methods for Early Leaf Drop Disease in Pomegranate

Early leaf drop disease includes several diseases. Based on lesion characteristics, it can be divided into brown spot disease, round spot disease, and ring spot disease, among which brown spot disease is the most serious. When the disease is severe, it causes massive early leaf drop, leading to premature tree decline, fewer flower buds, and reduced yield.

1. Symptoms

It mainly infects leaves. It first appears on leaves in the lower part of the canopy and in the inner canopy. The lesions of brown spot disease initially appear as small brown spots, then develop into needle-shaped, concentric ring-shaped, or mixed-type lesions. The small black particles on the lesions are the fungal spore discs. The lesions of round spot disease are initially circular or nearly circular, brown or gray spots. Leaves with ring spot lesions appear brown or dark brown and have prominent concentric rings, mostly occurring at the leaf margins and occasionally in the middle of the leaf. When the air is humid, black mold-like growth often appears on the underside of the leaves.

2. Pathogen

The above 3 leaf spot diseases all belong to the Fungi Imperfecti. The pathogen overwinters on fallen leaves as mycelial masses or spore discs, and in spring of the year forms spores that are spread by wind and rain. It first infects leaves in the lower part of the canopy, and after that undergoes multiple re-infections. With abundant rain and high humidity, the disease is quite severe; with little rain, the disease rarely occurs.

3. Control Measures

First, in autumn and winter, clear the fallen leaves in the orchard and burn them in a centralized manner or bury them deeply to reduce overwintering pathogens.

Second, during the growing period, spray 2-3 times with 1:1:200 Bordeaux mixture, or 50% Tuzet wettable powder 600 times solution, or 50% thiophanate-methyl wettable powder 800-1000 times solution, or 65% zineb wettable powder 500-800 times solution. The first application should be carried out before wheat harvest. When spraying, pay attention to spraying evenly and finely, and do not miss any areas. Both the underside and upper side of the leaves must be sprayed.

Third, strengthen comprehensive management, prune reasonably, improve ventilation and light conditions within the canopy, and reduce conditions and opportunities for pathogen occurrence.