How to prevent and control southern blight in nursery stock and flowers? Practical methods shared

What should you do when southern blight occurs on herbaceous flowers such as cacti, three-ribbed sword (Hylocereus undatus), impatiens, glasswort (Pellionia repens), iris, orchids and peonies?

When southern blight first appears, small dark brown wet rot patches form first on the stems and leaves at the base of the plant, followed by feathery white mycelium that then spreads to the soil surface. In humid conditions, the mycelium gradually turns into orange-red or reddish-brown rapeseed-like sclerotia, causing the stems to rot.

The mycelium and sclerotia of southern blight can survive in soil and plant debris for many years. They are most likely to harm succulents and cactus-type flowers, as well as herbaceous flowers with tender stems. In high temperature and high humidity conditions they spread very quickly over the soil surface, and alternating dry and wet conditions in the potting soil can inhibit the spread of the pathogen. After the disease appears, the plant should be removed from its pot and the soil replaced immediately. For contaminated soil, mercuric chloride, quicklime and water can be mixed in a weight ratio of 1:15:1500 and poured on as a disinfectant, or 25% quintozene at 0.1%-0.2% of the weight of the potting soil can be used for disinfection.

Before the disease appears and in its early stages, spraying with 500 times diluted 50% wettable carbendazim can be used for control. If wet rot is found at the base of a three-ribbed sword (Hylocereus undatus), it should be removed from its pot immediately, the rotted part cut off together with some healthy stem flesh, and the cut surface thoroughly dried until a skin film forms, then stood upright on moist plain sand to let it re-root; to prevent the three-ribbed sword from falling over, it can be tied to reed stakes for support.