How to prevent and control southern blight in flowers? Prevention and control of southern blight in flowers

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, and in severe cases the entire plant dies. So how should southern blight in flowers be prevented and controlled? Below is an introduction to the prevention and control methods for southern blight in flowers.

Southern blight mainly occurs on the roots and stem bases of plants. In woody flowers, it generally begins at the root collar near the ground and then spreads upward and downward underground. The diseased area first turns brown, and then the cortex rots. The leaves of affected plants lose water and wilt, wither and drop off, plant growth stalls, and flower buds develop poorly, becoming shriveled and turning red.

The main feature is that the diseased area is water-soaked, yellow-brown to red-brown wet rot, covered with a white silky mycelial layer that mostly spreads in a radial pattern and often spreads onto the soil surface near the diseased area. The cortex of the diseased area peels off easily, and the basal leaves drop off easily. In clivia and orchids, it occurs at the leaf stem area and the underground fleshy stem. In flower plants with corms and bulbs, it occurs on the corms and bulbs. In the middle and late stages of the disease, yellow-white sclerotia the size of rapeseeds often appear in the white mycelial layer, later turning yellow-brown or brown, becoming the source of reinfection.

The sclerotia formed by southern blight in flowers overwinter in the soil. The sclerotia can survive in soil for 5 to 6 years, and in water for only 3 to 4 months. When environmental conditions are suitable, the sclerotia produce hyphae to cause infection. The suitable temperature for the pathogen's development is 32 to 33°C, with a maximum of 38°C and a minimum of 13°C. Under high temperature and high humidity conditions, the disease is severe and spreads quickly; continuous cropping plots have severe disease; acidic sandy soil also promotes the occurrence of the disease.

Comprehensive measures should be taken to prevent and control southern blight in flowers:

(1) Eliminate the source of the disease. Promptly pull out diseased plants, and the sclerotia and diseased residues that fall into the soil should be gathered and burned or deeply buried. Apply lime in the diseased planting holes to kill the pathogen. Some sclerotia may be mixed in with flower seeds; when raising seedlings, they can be removed with 10% salt water or 20% ammonium sulfate, then rinsed with clean water before sowing.

(2) Pay attention to choosing the planting site. For plots with severe disease, continuous cropping cannot be practiced, nor should they be continuously cropped with crops susceptible to southern blight such as chili peppers, tea seedlings, pumpkins, and peanuts.

(3) Pay attention to drainage and fertilization in the garden, and strengthen management to enhance the disease resistance of the plants.

(4) Chemical control. Apply pesticides at the appropriate 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. Lime powder and plant ash can be spread around them for prevention. Plant ash has a very good effect on controlling southern blight in orchids. Plant ash is alkaline and, in addition to being rich in elements such as calcium, potassium, and phosphorus, also contains a large amount of silicon. After being absorbed by the root system, it can cause a hard layer of silicon to accumulate in the epidermal cells of orchid stems and leaves, enhancing disease resistance.

In addition, the calcium in plant ash reacts with the oxalic acid secreted by the hyphae of southern blight, producing calcium oxalate, which causes the pathogen to die. After spreading plant ash, the hyphae recede and the sclerotia dry up. Mildly affected plants can resume growth, and 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 plant ash leachate by watering, about once every 15 days, and 2 to 3 applications are sufficient. Spraying 1% Bordeaux mixture or 0.3 degree Baumé lime sulfur for control also has a certain effect. In addition, 5% wettable tecloftalam medicated soil can also be tried for control.