Control Methods for Edible Fungus Diseases and Pests and Orchid Anthracnose

Symptoms

Orchid anthracnose is caused by infection with anthracnose pathogens, with the leaves suffering the most severe damage, though other organs can also be affected. In the early stage of the disease, reddish-brown or dark-brown circular or elliptical spots appear in the middle of the leaves, while lesions at the leaf margins are semicircular. As the lesions expand, many small spots merge to form wavy or striped large dark-brown lesions. If the disease starts at the leaf tip, the lesions spread downward, causing segments of the leaf to die off; if it starts at the leaf base, the entire leaf may die in severe cases. In the late stage of the disease, the lesions appear to have concentric rings, and the center of the lesions becomes lighter, turning grayish-white; some lesions also develop longitudinal cracks.

Disease Patterns

The anthracnose pathogen begins infecting old orchid leaves in early April, spreads relatively quickly from May to June, worsens during the plum rain season, and gradually stops after July. New orchid leaves begin to show symptoms at the end of July and develop rapidly in August. If a typhoon strikes at this time, it can injure the leaves and plants, worsening the disease. The orchid anthracnose pathogen can survive on leaf surfaces for 9 months and in the plant for more than a year; even if the pathogen falls onto the surface soil of orchid pots, it can live for about a year. Therefore, once infected, if untreated, the disease will recur year after year.

Control Methods

To control orchid anthracnose, the first step is to strengthen the cultivation and management of orchids. Orchids kept indoors should have good ventilation and light transmission to reduce environmental humidity, while those grown outdoors in the open should have shade shelters built to avoid exposure to the sun and damage from sudden storms. Orchids should not be planted too densely, and a certain distance should be kept between pots. Water should be poured slowly onto the potting soil, avoiding drenching the entire plant, which would spread the pathogen downward. In winter and early spring of the following year, special attention should be paid to keeping the plants warm, protecting them from frost and freezing damage to enhance their disease resistance. In the early stage of the disease, diseased leaves can be pruned off to inhibit the spread of the disease. For chemical control, during the plum rain season and the typhoon season from July to September, spray on sunny days with 50% carbendazim wettable powder at 500 times dilution or 50% thiophanate-methyl wettable powder at 500 times dilution, once every 10 days or so, for 3-4 consecutive sprays.