How to treat southern blight? Scientific prevention and control methods to help you defeat the disease

OrchidMold disease, also known as southern blight, is a fungal disease, and the main pathogen is Penicillium spp. It first appears in the soil andorchidon the corm area, producing white mycelium, which then gradually spreads outward. Later, the mycelium tangles together to become chestnut-brown or blue sclerotia. The affectedorchidcorm area becomes water-soaked, rots and softens, and breaks easily. Within two to three days of onset, the white mycelium covers the entire orchid pot and can cause the whole pot oforchid plantsto rot and die completely. It is an extremely fast-killing and highly destructive pathogen. The main onset time is from June to July. In the past I often heard the older growers say that southern blight was terrifying, so I was always on the lookout for it. After growing orchids for several years without finding it, I became a bit lax. On August 3, the morning temperature was 32°C. I was off work, watered thoroughly, and inspected every pot of plants. I found nothing unusual, and they were all growing very well. I was quite pleased and in a good mood, so I went out to my teacher's shop to chat about flowers. On the morning of August 4, the temperature was 32°C. I watered thoroughly again, inspected, and found something unusual on the surface of a pot of spring sword orchid that had been collected from the wild around November last year. When I took it into strong light to look, I screamed: Oh no! The pot surface was covered with terrifying white mycelium, southern blight! My plants had caught southern blight! The wolf had finally arrived (as shown in Figure 1). I gently lifted a new shoot with my hand; the corm had completely rotted and turned into a mushy substance. It fell over at a touch and lifted up at a pull, and the wound color was light blue (as shown in Figure 4). I smelled the wound on the new shoot, and there was a mushroom-like odor. Fortunately, it was an early infection. After turning the pot out, I found that theorchid plantscorm areas were completely covered with white mycelium (as shown in Figures 2 and 3). Because it was discovered early, only the surface potting medium had this mycelium, and the deeper layers had not yet been affected. I quickly thought about how to treat it and whether it could be saved. So I pulled out the rotten shoots, removed all the dead leaf sheaths, removed the rotten roots, and took it under the faucet to wash it repeatedly with force, digging out all the rotten material. Only then did I discover that some old orchid corms had already been "gnawed" halfway away by the mycelium, exposing terrifying wounds. I did not know whether they could still be saved. After washing clean, I put it in a cool place (it was really too hot here; after noon, even a cool place was around 34°C). Before going to work in the afternoon, the water had completely evaporated and the roots had become soft, so I took out thiophanate-methyl, mixed it into a solution at a concentration of about 800, and soaked the plants in it. After coming home from work, I took them out and dried them again. The next day, that is, the morning of August 5, I took out a new pot and new potting medium (the old potting medium was spread out in the sun, and after killing the pathogen, it was thrown away; the pot needed to be sunned for a few more days and then disinfected before use). I planted the dried diseased plants, then mixed a copper-based fungicide with one kilogram of water and poured it like a thorough watering, from the leaves all the way down to the roots. After pouring all one kilogram of water, I placed it in a cool place and did not water again. After dry cultivation for three days, I mixed it with the other plants and managed it normally. To date, this diseased plant has shown no signs of recurrence. Analyzing the cause, I used a tall ceramic pot and large-particle soil, and by August the temperature was already as high as 37.8°C, so it should not have been the onset period for southern blight. It may have been because the place where it was placed was relatively cool. In addition, when this plant was collected from the wild last year, it came in together with some other plants. The weather was freezing and the water was ice-cold, so I estimate that during pruning and washing (the water was too cold, it froze my hands), I was a bit too careless and did not remove some dead leaf sheaths. The "seeds" of southern blight may have been hidden inside. Although it had also been disinfected and sterilized, there were still pathogens that slipped through the net. Combined with the cool placement location, the southern blight mycelium grew wildly. When cleaning this pot of plants, I found that the place with the most southern blight mycelium was the corm area of the old plants, and when I tore open the leaf sheaths, I also found a lot of mycelium. Because old plants have much stronger resistance than new shoots, southern blight had not yet completely "gnawed" all the old plants clean. Two more days, and this whole pot of plants would have been utterly wiped out. But this year's new plants were effectively grown for nothing; not a single shoot remained. I remind orchid friends to pay attention: southern blight mycelium is easily found on wild-collectedorchid plants. Once found, wash them clean promptly and treat them with disinfection and sterilization, and be careful to wash away the mycelium inside the leaf sheaths. During the high-incidence season of southern blight, observe more often and solve problems promptly when found. For severe disease, use strong medicine, so the concentration of the medication can be the highest concentration the orchid plants can tolerate, and the soaking time should also be extended. In addition, southern blight has not been found to show signs of spreading between two pots, unless when pouring water heavily the mycelium is washed into other flower pots; or the two pots are really too close together, even with the potting soil touching, and no attention is paid to it, so after the mycelium grows all over, it climbs over the pot (if this happens, then theorchid growerwas being a bit derelict in duty). The orchids placed around this diseased pot grew well, and no southern blight was found. However, to be safe, I still treated all the orchids in the entire orchid shed with a fungicide once. After all, when watering thoroughly, the force is quite strong, and if any mycelium that slipped through the net were washed into other pots, I would not even be able to cry. After this "battle," I finally gained a preliminary understanding of southern blight. The lesson was profound and also worthwhile. I hope orchid friends everywhere will also raise their vigilance. Strictly do a good job of disinfecting and sterilizing wild-collected orchids to prevent even more serious pathogens from harming orchid plants. Excerpted from "Orchid Treasure Book," Chongqing, Qinghong