How to prevent and control anthracnose and leaf spot disease in orchids

Orchids, belonging to the family Orchidaceae as ornamental plants, commonly suffer from anthracnose and leaf spot disease.

1. Orchid anthracnose: It mainly damages the leaves. In the early stage of the disease, dark brown spots appear on the leaves, surrounded by a faded green halo. After the spots expand, they become oval or elongated. The edges are dark brown, the interior is yellowish brown, and the spots are slightly raised. In the later stage, black granular bodies appear on the spots. Under humid conditions, the black granular bodies extrude pink colloidal matter, which is the acervulus and conidial mass of the pathogen. Anthracnose occurs over a long period, with the most severe incidence in July and August.

Prevention and control: (1) Ensure good ventilation and light transmission. (2) Fertilize reasonably to improve disease resistance. During the growing period, control the application of nitrogen fertilizer and appropriately apply more phosphorus and potassium fertilizer. (3) In the early stage of the disease, spray 50% carbendazim or 70% thiophanate-methyl wettable powder at 500-800 times dilution.

2. Orchid leaf spot disease: It is a fungal disease that damages leaves and can occur throughout the entire growing period. High temperature and high humidity, damage by scale insects, and poor ventilation all make leaf spot disease more likely to occur.
In the early stage of leaf spot disease, the spots are brown. After expansion, the spots become long oval to elongated streaks, with reddish brown edges and grayish brown interiors. In the later stage, black granular bodies are scattered on the spots.

Prevention and control: (1) Improve ventilation conditions and eliminate pests. (2) In the early stage of the disease, spray 50% tebuconazole at 1000 times dilution or 65% zineb at 800 times dilution for control.