Practice of Orchid Phytophthora Control

Control practice of orchid blight (including stem rot)

Phytophthora: The pathogen of a disease is Phytophthora.

This disease is one of the worldwide orchid diseases. It has not appeared in China before, but in recent years, it has occasionally occurred locally. The parts infected by blight fungi are wet and rotten, and black after drying, so they are also called "black rot". Although the spots of black rot and blight are the same in late stage, the affected parts of blight are different from those in early stage. The disease usually occurs from the lateral edge of the middle part of mature leaves. However, it can vary according to local climatic and ecological conditions. Some can start from leaf base or leaf tip first, some are roots, stems, leaves and flowers are fully damaged. In the early stage of injury, the leaf color remains unchanged, and the affected parts, like being rubbed and injured, are wet and dark green; after drying, they turn black. The part of tissues not directly affected withered and turned black due to the destruction of conducting tissues.

Orchid blight, also known as "water injury", is a fungal disease caused by Phytophthora infestans and Pythium terminale. Because of its occurrence site and different diseases, it can also be divided into black rot, heart rot, stem rot, damping-off disease and so on. Phytophthora infestation easily caused root rot, damping-off and root neck rot, while ultimate infection caused root rot and damping-off of plants. Chinese orchid leaves near the base of the bud infected disease, initially the leaf color faded green or water-soaked, and then gradually expanded into light brown to black-brown corruption, until the whole plant dried up and died. The disease is not easily distinguishable from white silk disease and Fusarium rot. It can occur all year round in the south where the climate is warm, but it is most serious in the rainy season in spring when the humidity is high, the ventilation is poor and the sunshine is insufficient. Pathogenic bacteria can be spread by rain splash, but also by snails, slugs and other feeding group sowing.

To prevent orchid blight, we should pay attention to avoid excessive moisture, and make good ventilation and sufficient sunshine. At the early stage of disease, disinfected blades were used to excise diseased tissues, and 70% mancozeb WP 600-800 times or 25% metalaxyl WP 500-800 times were sprayed. Apply every 7 days for 2-3 consecutive doses. Severe cases should be removed and destroyed immediately. At ordinary times, attention should be paid to the prevention and control of snails and slugs to avoid the spread of diseases.

I hope it is useful for beginners.