How to prevent and control the main diseases of flower seedlings
Spring is a favorable time for raising seedlings of many flowers such as scarlet sage, wax begonia, and mallow. However, because spring weather is changeable and cold spells often occur, conditions are often favorable for the occurrence of various diseases during the flower seedling stage. The occurrence of the main diseases during the spring flower seedling stage and their control methods are described below.
Damping-off: Seedlings that have not yet emerged or have just emerged can all become diseased. When seedlings have not yet emerged, the embryo and cotyledons rot. When emerged seedlings become diseased, water-soaked lesions appear at the base of the young stem, after which the diseased part turns yellow-brown, shrinks and becomes thin, and the seedling breaks off as soon as it is pulled. When this disease occurs in the seedbed, at first only individual seedlings are affected, but after a few days, with these as the center, it spreads rapidly to neighboring plants, causing patches of seedlings to collapse. When humidity is high, a layer of white cotton-like mycelium grows on the diseased parts of the host and on the surrounding soil surface. The pathogen overwinters in the soil in the form of oospores and, under suitable conditions, germinates to produce zoospores or directly produces germ tubes that invade the host. The pathogen spreads through rainwater or the movement of water in the soil. When seeds and seedbed soil carry more pathogen, seedlings have more opportunities to become infected. Low soil temperature, high seedbed humidity, and insufficient light make plants prone to the disease. Herbaceous flowers such as garden balsam and cockscomb that are propagated by sowing and raising seedlings are more commonly affected and suffer more severe damage.
Control methods
1. Choose the seedbed site well. For the seedling-raising site, choose soil with slightly higher terrain, good drainage, loose and fertile texture, good aeration, and no previous cultivation of disease-susceptible flowers as the seedbed soil.
2. Disinfect the seedbed soil. For each square meter, use 7 to 8 grams each of 65% zineb and 50% carbendazim, or 5 grams of 70% dexon, and mix with 15 kg of dry fine soil to make medicated soil. When sowing, first use 1/3 of the medicated soil as a base layer, and after sowing use the remaining 2/3 of the medicated soil as a cover layer.
3. Disinfect the seeds. Before sowing, sun-dry the seeds for 1 to 2 days, then soak them in a 250-fold dilution of 50% carbendazim for 24 hours. This can kill the pathogens carried on the seeds.
4. Chemical control. When seedlings first become diseased, irrigate the diseased plants with a 1000-fold dilution of 80% techtosan, or spray with a 600-fold dilution of 25% metalaxyl, once every 7 days, for 2 consecutive sprays, which can effectively control the spread of the disease.
Root rot mainly harms seedlings, and can also occur at the mature plant stage. In the early stage of the disease, only individual lateral roots and fibrous roots become infected, and it gradually spreads to the main root. After the main root is infected, the plant shows no symptoms at first, but later, as the degree of root rot intensifies, its ability to absorb water and nutrients gradually weakens. Because the aboveground part cannot obtain sufficient nutrients, only when light is strong and evaporation is high around noon do the upper leaves of the plant wilt, but they can recover at night. When the disease is severe, the wilting cannot recover even at night. At this point, the root bark turns brown and separates from the pith, and finally the whole plant dies. This disease often has symptoms similar to root drowning and is a fungal disease. The pathogen overwinters in the soil and on diseased residues. It generally occurs from late March to early April, and enters its peak period in May. Its occurrence is closely related to climatic conditions. Low temperature, high humidity, and insufficient light in the seedbed are the main environmental conditions that trigger this disease. When the seedling-raising soil is highly clayey, easily compacted, and poorly aerated, root growth and development are hindered, and the disease is also likely to occur. In addition, after roots are damaged by underground pests and nematodes, there are many wounds, which favors pathogen invasion. Under these conditions, not only are herbaceous flowers propagated by sowing and cuttings susceptible, but woody flowers propagated by cuttings, division, and layering, such as rose, cotton rose, and Chinese hibiscus, are also prone to the disease.
Control methods
1. Disinfect seeds and cuttings. Before sowing, seeds can be treated with techtosan at 0.3% of seed weight or triadimefon at 0.1% of seed weight, or soaked in a 2000-fold dilution of 80% 402 antibacterial emulsifiable concentrate for 5 hours; the base of cuttings can also be soaked in the same concentration of the solution for 1 hour before planting.
2. Disinfect the seedbed soil. For each square meter, scatter 1.5 grams of 50% carbendazim on the surface and turn it into the soil, or use 3 grams of 75% quintozene, both of which are effective and can also control damping-off and seedling blight.
3. Chemical control. When the disease occurs, spray or irrigate the diseased plants with a 1000-fold dilution of 40% root rot ning; or drench the roots with a 1500-fold dilution of 80% 402 emulsifiable concentrate.
4. Timely control underground pests and nematode damage.
Southern blight mainly damages the base of seedling stems. When it first occurs, water-soaked, irregular brown lesions appear on the stem near the root, the cortex soft-rots, and then it expands to encircle the entire stem base. On the surface, white silky mycelium is produced, which can spread to the surrounding soil surface to form a white silky network. Later, the mycelium gradually aggregates into many small white granules, which gradually become pale yellow, yellow, light brown, and finally brown rapeseed-like sclerotia. In the late stage of the disease, the stem base and the entire root system rot and die. The pathogen overwinters in the soil or in diseased plant residues as sclerotia or mycelium. In the following spring, mycelium is produced for infection. Soil fertilizer mixed with diseased residue tissue that has not decomposed can also transmit the disease. Repeated infection in the nursery (bed) relies on mycelial expansion, contact between diseased and healthy plants, flowing water, and management operations. If diseased plants appear in the field, mycelium in the soil around the diseased plants can spread along soil cracks or the ground surface to neighboring plants. Mycelium generally invades directly from the base of the host stem, and more easily invades through stem wounds. Disease occurrence is closely related to temperature, humidity, and pH. High temperature and high humidity, overly acidic soil, plants spaced too densely, and poor ventilation and light transmission are favorable for disease occurrence. Surveys have found that flowers such as garden balsam, orchid, peony, clivia, chrysanthemum, Chinese peony, evergreen, iris, daphne, and jasmine are susceptible.
Control methods
1. Soil disinfection. Whether potted or field-grown, the soil should be disinfected. For each square meter, use 1.5 grams of dinong emulsifiable concentrate mixed with 25 kg of fine soil and broadcast it, then turn it into the soil.
2. In the early stage of the disease, use 0.5 kg of 75% quintozene plus 20 kg of fine soil to make medicated soil and scatter it on the ground around the stem base, or spray a 800-fold dilution of 45% amobam on the plant base and the surrounding soil; or irrigate the diseased plants with a 2000-fold dilution of 25% triadimefon. All of these can effectively control the occurrence and spread of the disease.