Control methods for orchid basal rot and southern blight

With the continuous improvement of people's living standards,orchid growingand orchid appreciation, as elegant leisure activities, are increasingly favored by urban residents. However, in theprocess of growing orchids, because each orchid lover'sorchid growingenvironmental conditions andcultivationexperience differ, success and failure in growing orchids also vary. And almost every orchid grower will inevitably encounterthe orchid'snumber one "killer" - southern blight. Thus, many topics about southern blight have arisen among orchid growers. And this article is a lengthy piece attempting to reveal the causes of southern blight. I. Causes of southern blight: From May to August each year, most regions of our country have entered the high-temperature, rainy season. And this is precisely the season whenorchidssprout and grow. Many orchid growers' growing environments are not as ideal as one would wish,orchid plantsare confined to pots, and orchid roots cannot stretch out freely, which already restrictsorchid plantgrowth. If, in addition, there is insufficient shading, poor drainage, and poor ventilation,orchid plantsbecome highly susceptible to disease and pest damage. To prevent and control disease and pest damage to orchid plants, people often spray various chemicals and fertilizers on the orchid plants; whether applied properly or not, varying degrees of chemical and fertilizer residue deposit at the leaf sheaths and the orchid heart. These chemicals and fertilizers, soaked for long periods on the extremely delicate leaf bases, easily damage the leaf stems, especially the tender new shoots. If, in addition, drainage is poor and ventilation is poor, the chemicals and fertilizers retained in the leaf sheaths mix with the water from watering, and together with the effect of high temperature, a chemical reaction occurs in the leaf sheaths, scorching the leaf bases and causing the orchid plant to die off - that is, orchid basal rot. If basal rot is not discovered in time, the rotting plant will give rise to a virus that can spread rapidly, namely the southern blight fungus appearing as white thread-like bodies; this is the cause oforchidsouthern blight. II. Southern blight should focus on prevention: Now that we know the cause of southern blight is water accumulation in the sheath leaves, which is scorched under high temperature, we can effectively prevent the occurrence of southern blight. Shallow planting is the first essential factor in preventing and controlling southern blight. Most orchid growers know the principle that deep planting easily producesflowers. In order to obtain more robust seedlings, we can add growing medium to the orchid plants after autumn, and after the new shoots emerge, remove part of the growing medium so that the pseudobulbs are half-exposed or fully exposed above the soil surface; in this way, water does not easily accumulate in the leaf sheaths, or if there is occasional water accumulation, it evaporates relatively easily, which can effectively prevent the occurrence of orchid basal rot and southern blight, and also yield more robust new seedlings, and make it easier to see flowers. Then, is there a corresponding standard for deep planting or shallow planting? As the saying goes: there is no fixed formula. Deep planting or shallow planting should also vary according to the differences in orchid growing environment andcultivationsubstrate. Generally, for orchids grown on the ground, the air humidity is correspondingly higher, the temperature correspondingly lower, and the light correspondingly softer; when planting common orchid varieties, the pseudobulbs may be slightly exposed above the soil surface. If the seedlings emerge in the shape of winter bamboo shoots, then shallow planting is suitable. That is, the pseudobulbs should sit on the soil surface; then use sphagnum moss or granular sawdust to cover the bulbs so as not to let them dehydrate. If orchids are grown on a balcony or rooftop, then because the environment is extremely harsh, with low air humidity, overly strong light, overly strong dry winds, and fierce rain, if in addition the substrate has poor water permeability, it is very easy for rain and watering to accumulate in the pot soil; if this is further combined with high temperature or direct sun exposure, it is very easy to trigger basal rot, and then lead to the spread of southern blight. Therefore, all those who grow orchids on balconies or rooftops should try to avoid direct sunlight on the orchid plants, avoid rain washing over the orchid plants, and from May to September, watering should be done after 8 p.m. as much as possible. This is because by then the heat in the orchid pot has gradually dissipated, and watering thoroughly once is equivalent to giving the orchid a cool rinse. And after a night of dripping, the orchid pot basically no longer holds accumulated water; when the temperature gradually rises the next day, local heat transpiration will not occur due to overly wet substrate being baked at high temperature, which would scorch orchid roots and new shoots and invite basal rot and southern blight. However, how should basal rot and southern blight that have already occurred be handled? Based on my own experience, the author believes: First, quickly remove the plant from the pot, use a sharp knife to cut away the diseased parts, and split open or remove the leaf sheaths of the uninfected plants, rinse clean with running water, especially the leaf sheaths and the gaps at the leaf bases, which should be carefully rinsed. After washing, place the orchid plant upside down to drain, making sure that water accumulates in the leaf sheaths and leaf gaps is completely drained and air-dried. Then, use a fungicidal powder such as copper hydroxide, chlorothalonil, carbendazim, thiophanate, etc., choosing any one, and dust the dry powder onto the pseudobulbs, making sure the powder fully coats the pseudobulbs. After that, plant in a pure growing medium (clean river sand is best), making sure the pseudobulbs float above the surface, and after planting do not water immediately; wait three to five days before watering. Treated this way, most can preserve the variety. And in the same year or the next year new orchid plants will sprout, and in two to three years the orchid plants can be rejuvenated. After the orchid plants are rejuvenated, the new seedlings should be separated from the original diseased plants, and the separation wounds should be coated with fungicidal powder, then planted in new growing medium. The above is purely the author's humble opinion, for the reference of fellow orchid growers only. Address: Tianxiang Orchid Garden, No. 30 Wenchang Road, Hengtai New Village, Shaowu City, Fujian Province: Yang Yonghua Phone: 0599-6220528 Postal code: 354000