What are the control methods for brown rot in orchids?
Brown rot in orchids often first appears on new leaves. Its pathogen invades from the roots, and purple or purplish-brown lesions first appear on the leaf bases and pseudobulbs, gradually becoming water-soaked, and the lesions also expand accordingly. After 3 to 5 days from onset, the leaves soften and turn dark brown, while the vascular tissue of the pseudobulbs turns black, and before long they rot and fall off, until the entire plant turns black and dies. The pathogen spreads through the vascular tissue of the pseudobulbs and through external contact, and will quickly spread to healthy plants around the diseased plant, and within a few days can affect the entire pot.
Brown spot in orchids occurs more often on seedlings of Cattleya and Phalaenopsis. Its causes are:
1. It is prone to occur during periods of high temperature and abundant rain.
2. Soil compaction or excessive water content, poor air permeability.
3. Fertilizer applied too concentrated or in too large an amount.
4. Mechanical damage to the pseudobulbs, allowing the pathogen to invade.
For brown spot in orchids, prevention should be more important than cure. The specific control measures are as follows:
1. In the high-temperature and rainy season, June to August is the period of frequent occurrence. Orchids must be carefully observed every morning and evening, and prevention strengthened. Once lesions are found on potted orchids, they should immediately be isolated from healthy orchids.
2. Maintain ventilation and air exchange in the cultivation environment, including the site and the potting soil. Frequently clear away surrounding dead branches and fallen leaves, and burn them thoroughly. Spray disinfectant on benches, greenhouses, paths, and pots.
3. Water should be poured in from the edge of the flower pot, avoiding overhead watering, so that water droplets do not carry residual spores to other healthy plants. Watering should be done at the time when it dries most easily, avoiding excessive watering and overly wet potting soil, and water must not be poured into the leaf axils.
4. When dividing plants, the cutting blade should first be disinfected, and carbendazim powder should be applied to the wounds or they should be soaked in streptomycin solution for 60 minutes.
5. In the early stage of the disease, spray 2 to 3 times with 50% carbendazim powder at 500 times dilution or Bordeaux mixture at 100 times dilution.
6. Diseased plants should be repotted with fresh soil. The culture soil of diseased orchids cannot be used again. The damaged parts of diseased plants must be thoroughly cut off and burned. After repotting, the diseased plants and potting soil should be sprayed with Bordeaux mixture once every 10 days.