How to prevent and treat Southern blight in ornamental flowers? A detailed guide to practical methods

Southern blight is a common disease of ornamental flowers. Its host range is very broad, and after infection it causes the roots and stem bases of these flowers to rot; in severe cases, the entire plant dies. Southern blight occurs mainly on the roots and stem bases of plants. In woody flowers, it generally begins at the root crown near the ground and then spreads upward and downward underground. The diseased part first turns brown, and then the cortex rots. The leaves of affected plants lose water and wilt, wither and fall off, plant growth stalls, and flower buds develop poorly, becoming stiff, wilted and reddened. The main feature is that the diseased part is water-soaked, yellowish-brown to reddish-brown wet rot, covered with a layer of white silky mycelium, mostly spreading radially, often spreading onto the soil surface near the diseased part; the cortex of the diseased part peels off easily, and the basal leaves fall off easily. In clivia andorchidsand others, it occurs on the leaf stems and underground fleshy stems. In flower plants with corms and bulbs, it occurs on the corms and bulbs. In the middle and late stages of the disease, yellowish-white sclerotia the size of rapeseeds often appear in the white mycelial layer, later turning yellowish-brown or brown, becoming the source of reinfection. The sclerotia formed by flower Southern blight overwinter in the soil. The sclerotia can survive in the soil for 5 to 6 years, and in water for only 3 to 4 months. When environmental conditions are suitable, the sclerotia produce mycelium to cause infection. The suitable temperature for the pathogen's development is 32 to 33°C, with a maximum temperature of 38°C and a minimum temperature of 13°C. Under conditions of high temperature and high humidity, the disease is severe and spreads quickly; continuous cropping land has severe disease; acidic sandy soil also promotes the occurrence of the disease. Comprehensive measures should be taken to prevent and treat Southern blight in flowers: (1) Eliminate the source of infection. Promptly pull out diseased plants, remove sclerotia and diseased residues that have fallen into the soil, burn or bury them deeply in a concentrated way, and apply lime in the diseased holes to kill the pathogen. Some sclerotia may be mixed in with flower seeds; when raising seedlings, a 10% salt solution or 20% ammonium sulfate can be used to remove the sclerotia, then rinse with clean water before sowing. (2) Pay attention to choosing the planting site. For plots with severe disease, do not practice continuous cropping, and do not rotate continuously with crops susceptible to Southern blight such as chili peppers, tea seedlings, pumpkin and peanuts. (3) Pay attention to drainage and fertilization in the garden, and strengthen management to enhance the disease resistance of plants. (4) Chemical control. Apply pesticides at the right time in the early stage of the disease to control the epidemic. Promptly pull out diseased plants, and use 70% quintozene medicated soil at 1 to 2.5 kg per mu mixed evenly with an appropriate amount of fine soil for disinfection. Around them, lime powder and plant ash can be spread for prevention. Plant ash is very effective in controllingorchidSouthern blight. Plant ash is alkaline; besides being rich in elements such as calcium, potassium and phosphorus, it also contains a large amount of silicon. After absorption by the root system, it can cause the epidermal cells oforchidstems and leaves to accumulate a hard layer of silicon, enhancing disease resistance. In addition, the calcium in plant ash reacts with the oxalic acid secreted by the mycelium of Southern blight, forming calcium oxalate and causing the pathogen to die. After spreading plant ash, the mycelium recedes and the sclerotia dry up. Mildly affected plants can resume growth; for more severely affected ones, the root system and pseudobulbs basically return to normal, and with proper management new shoots can sprout. To prevent the occurrence of the disease, apply a plant ash extract by watering, once every 15 days or so, 2 to 3 times is enough. Spraying 1% Bordeaux mixture or 0.3 Baume lime sulfur for control also has a certain effect. In addition, 5% wettable tecloftalam medicated soil can also be tried for control. (Cao Dihuan)