Occurrence and Control Methods of Stem Rot in Flowers and Nursery Stock

Stem rot in flowers and nursery stock is a disease caused by fungi of the order Sphaeropsidales in the class Deuteromycetes. This disease can harm many plants; one-year-old ginkgo seedlings are the most susceptible, with a mortality rate of over 80%. In addition, it also harms the seedlings of forest trees such as pine, cypress, Chinese Torreya, golden larch, eucommia, sweetgum, black locust, chestnut and dawn redwood. After different nursery stocks are infected, their symptoms are not entirely the same, but they generally manifest as stem rot. For example, after one-year-old ginkgo seedlings are infected, the initial symptom is that the stem base turns brown, the leaves lose their normal green color and droop slightly downward; after the diseased part rapidly develops upward, the whole plant dies, with the leaves drooping but not falling off. The cortex of the diseased stem becomes swollen and wrinkled, and the epidermal tissue rots into a spongy or powdery form; the pathogen invades the xylem, causing the pith to turn brown or become hollow. After the disease spreads to the roots, the root cortex rots; if the diseased seedling is pulled up, only the xylem can be pulled out while the root cortex remains in the soil. For two-year-old nursery stock infected or one-year-old nursery stock with mild disease, part of the aboveground portion of the diseased seedling dies, and new branches can sprout from the base in the same year. In hot summers, the soil temperature rises; when the stem base of the nursery stock is scorched by high temperature, the pathogen invades and causes harm. If the nursery land is low-lying and prone to water accumulation, the nursery stock grows thin and weak, and the incidence rate increases significantly. According to observations, nursery stock generally begins to develop the disease 10 to 15 days after the plum rain ends, after which the incidence rate gradually increases, and the disease stops occurring in mid-September. To control stem rot, comprehensive control measures should be adopted: First, choose land with a low groundwater level and good drainage as the nursery, and for container seedling cultivation, use soil free of pathogens to prepare nutrient soil; adhere to a crop rotation system and do not continuously cultivate the same kind of nursery stock on the same plot. Second, kill the pathogen. The stem rot pathogen is a soil-borne pathogen that usually lives saprophytically in the soil. Before raising seedlings, dry branches, dead leaves and dry grass can be evenly scattered on the seedbed and burned to kill the pathogen in the soil. Alternatively, 25 kg of lime powder or 15 to 20 kg of ferrous sulfate powder can be applied per mu of nursery land to inhibit the pathogen. Third, apply decomposed fertilizer. Fertilizer should be mainly farmyard manure, supplemented by chemical fertilizer. Garbage manure, compost and barnyard manure may carry the pathogen and should be piled, fermented and thoroughly decomposed before use. Generally, 40 to 50 loads of decomposed fine cattle pen manure are applied per mu of seedbed. Using plant ash as base fertilizer, 50 to 60 loads per mu, has good fertilizer efficiency and also good disease prevention effect. Fourth, build shade sheds in high-temperature seasons, which can lower the seedbed temperature and reduce the incidence rate by more than 85%. Fifth, improve the disease resistance of seedlings; timely cultivation and weeding, thinning, and topdressing should be carried out so that the seedlings emerge neatly and grow robustly. From the emergence stage, 50 to 75 kg of Bordeaux mixture per mu of nursery should be sprayed on the seedlings to form a protective film on the surface of the seedlings and prevent the pathogen from invading. After the disease occurs, promptly remove diseased seedlings and scatter lime powder around the holes of diseased seedlings to prevent spread. Inserting pine branches into the seedbed, or interplanting crops or green manure in the nursery, and irrigating to resist drought during dry periods also have a certain effect on reducing the incidence rate.