What to Do When an Orchid Gets Brown Rot? Detailed Prevention and Treatment Methods

Prevention and Treatment of Orchid Brown Rot

Because of the high temperatures of midsummer, excessive watering, soil that is too wet, compacted and poorly aerated, and mechanical damage to the pseudobulbs, orchids are very prone to brown rot. Its pathogens are quite varied, mainly Phytophthora palmivora and a small amount of Phytophthora nicotianae. When the disease strikes, water-soaked blotches usually appear on the leaf bases and pseudobulbs of one- to two-year-old plants, and the affected parts then gradually soften, turning light brown to dark brown; at the same time, the vascular tissue of the pseudobulbs turns black, the central leaves wilt, and yellowing spreads from top to bottom. Orchids are mostly planted in dense clumps with pseudobulbs connected to one another, so the pathogen spreads through the vascular tissue of the pseudobulbs and by external contact, quickly reaching the healthy plants around the diseased one. The disease progresses rapidly, and within a few days it can affect the whole pot. June to August, with its high temperatures and frequent rain, is the peak period for brown rot. Observe orchids carefully every morning and evening, and strengthen prevention. In addition to sterilizing the potting soil by roasting or sunning it when repotting orchids, spray once every 10 days with Bordeaux mixture at the equal-strength formula or 50% Tuzet wettable powder at 800 times dilution. Once disease spots are found on the leaves of an orchid in a pot, it should immediately be isolated from healthy orchids, the potting soil replaced, and the diseased plant thoroughly cut away with a sterilized single-edged razor blade and burned. For the healthy plants kept, rinse the roots with clean water and cut off the rotted roots. If only 1 to 2 shoots can be kept and the root system is too poor, with the orchid leaves dehydrated and shrunken, cut the leaves back by half or more, then immerse the whole plant completely in a 0.3% potassium permanganate solution and take it out; apply Tuzet or carbendazim powder to the wounds, place the plant with roots facing up and leaves facing down, and let it dry in a shady place for more than 10 minutes; then replant it in sterilized potting soil (or mix 65% zineb at 600 times dilution with bamboo-root mud). The potting soil of a diseased orchid must not be used again.

After repotting, orchids should be kept in a cool, shady place for care, with attention to ventilation and light. Do not fertilize in the same year, and keep the potting soil slightly dry. When watering, do not let water pour into the heart of the leaves. Mist with clean water in the morning and evening, just enough for fine, even droplets to appear on the leaf surface without running off. To the water used for misting, add monopotassium phosphate and urea at 0.05% each, to replenish the nutrients consumed by the repotted orchid and also to encourage new roots and new shoots. Growth can resume after one month. With careful management, leaf shoots will still emerge in the same year.