Causes of Lily Disease Epidemics and Integrated Control Techniques
I. Symptoms: They appear on leaves, stems and bulbs. When leaves are infected, leaf blight results. At first the leaf tip turns brown, with a length of 1-2 mm, then gradually worsens, and the lesion expands into a nearly triangular shape, becomes thinner, and takes on a dried-up appearance with cloud-like patterns on it. Lesions are generally 17-28 mm long and 5-8 mm wide; the largest lesion is 56 mm long and 12 mm wide. Eventually the leaf dies. Some also occur at the leaf margin as semi-elliptical brown lesions, which can also cause leaf death.
The lesions on the portion of the aboveground stem that enters the soil are brown dots or longitudinal streaks, slightly sunken, and in severe cases cause the stem to break and fall over. After the bulb is infected, many brown or dark brown nearly circular, short stripe-shaped or irregular lesions of varying sizes appear on the outer scales, slightly sunken, and cause the scales to turn yellow; in severe cases the bulb rots. The above symptoms often appear together on the plant; that is, once the disease occurs, the plant simultaneously shows leaf blight and lesions on both the bulb and the portion of the aboveground stem that enters the soil, and several pathogens can be isolated at the same time from the diseased parts, rather than one symptom being caused by only one pathogen.
II. Pathogens: Diseased plants collected from the field were identified by the Institute of Plant Protection of the Gansu Academy of Agricultural Sciences, and there are four kinds:
1. Colletotrichum sp., which can be isolated from the stems, leaves and bulbs of lilies. 2. Alternaria sp., isolated from the leaves. 3. Fusarium sp. 4. Rhizoctonia sp. Both 3 and 4 were isolated from the stems. These pathogens overwinter in the soil, in diseased plant residues and on planting material, and are the source of primary lily disease infection the following year. Under suitable conditions they can cause re-infection. They cause continuous disease occurrence, and are mainly spread by rain, wind and splashing surface water. In recent years the pathogens have jointly harmed lilies, causing combined symptoms that lead to lily leaf blight and yellowing of the bulbs, and in severe cases the death of the whole plant.
III. Main factors in disease epidemics
3.1 Continuous cropping: In lily-growing areas, the same plot is generally continuously cropped for 5-7 years, and in some cases for more than 10 years, which provides conditions for the accumulation of pathogens in the soil and is also an important basis for disease epidemics. In surveys in the old production areas of Pingchang, Gan'an, Youhe, Wujiazhuang and other townships, the rate of continuously cropped fields was 100%, the rate of diseased fields was 10%, and the rate of diseased plants was 15-36%.
3.2 Waterlogging damage: Lilium lancifolium likes a warm, dry climate and is suitable for growing on sandy soil. The current growing areas are old rice areas, and the soil is mainly paddy soil. In addition, the three ditches are not built to standard, so waterlogging is likely to occur. Waterlogging not only affects the normal growth of lilies and reduces disease resistance, but also provides conditions for the invasion and development of pathogens, becoming the main factor in lily disease epidemics. A 4-year survey found that in years with a lot of rain, the disease became epidemic, and that fields with standing water had more severe disease.
3.3 Pathogen-carrying seed bulbs: The lily planting material used is generally selected from that year's lily bulbs. Because field diseases are not effectively controlled, most harvested bulbs carry pathogens, which provides a pathogen basis for the spread of lily diseases and disease occurrence the following year. In our survey of newly developed lily-growing areas, the seed infection rate was 93%, and disease occurred in the same year, with the rate of diseased fields reaching 100%.
3.4 Fertilizer damage: Improper or excessive fertilization can cause the lower leaves of the plant to turn yellow and dry up prematurely, reducing the disease resistance of lilies. Farmers habitually use ammonium bicarbonate as a base fertilizer, or use pig manure, cow manure and other undecomposed organic fertilizers as base fertilizer, and the application rate is large, generally about 300 kg/mu. Because of excessive fertilization, the normal growth of lilies is affected, and conditions are also created for the invasion of pathogens.
3.5 Density: High density causes insufficient light in the lower part of the plants, makes the field crowded and poorly ventilated, affects normal growth, and favors pathogen infection. The plant and row spacing for lily planting is 10 cm x 13 cm, equivalent to about 50,000 plants per mu.
3.6 Density: High density causes insufficient light in the lower part of the plants, affects the normal growth of lilies, makes the field crowded, and results in poor ventilation, affecting normal growth and favoring pathogen infection. The plant and row spacing for lily planting is 10 x 13 cm, equivalent to 50,000 plants per mu.
IV. Control measures
4.1 Agricultural control: Crop rotation: Because some pathogens that infect lilies can survive in the soil for 2-3 years, in severely affected plots, lily planting should be stopped for 3-4 years, and in generally affected plots, for 2-3 years. Paddy-upland rotation is best. Do not rotate with crops of the same family.
Scientific fertilization and rational close planting: Creating a favorable growing environment and improving disease resistance is an effective way to prevent the occurrence of lily diseases. In terms of fertilization, use more phosphorus and potassium fertilizers and decomposed organic fertilizers as base fertilizer, and use little or no inorganic nitrogen fertilizer. For disease prevention, 20 kg of crushed seed cake can be used per mu, soaked in water until rotted (about one week), then mixed with 50 kg of plant ash and used as base fertilizer. Rational close planting is advocated, with plant and row spacing of 16.5 x 20 cm or 13.2 x 25 cm, that is, 20,000-25,000 plants per mu, and no more than 30,000 plants at most.
Build the three ditches well and change wide beds to narrow beds: When preparing the land, the three ditches must be built well. Change the old habit of shallow ditches and wide beds to deep ditches and narrow beds to facilitate drainage. Standards for the three ditches: the bed ditch is 30 cm wide and 25 cm deep, the middle ditch is 40 cm wide and 30 cm deep, and the surrounding ditch is 50 cm wide and 45 cm deep, and every ditch must have a slope so that the ditches dry after the rain stops. The bed surface must be level, changing the original 4 m width to 2-2.5 m. For overly long fields, a middle ditch should be opened every 15-20 m.
Remove diseased residues: Some pathogens of lily diseases can survive on diseased residues for more than 15 months. Therefore, when preparing the land, lily diseased residues must be removed and burned in a centralized manner to reduce the primary infection pathogens of lily diseases.
4.2 Soil treatment: Soil-borne fungi are the main mixed pathogens causing lily diseases. In soil treatment, the following can be adopted: when preparing the land, broadcast 50 [kg] of quicklime per mu, then plow the land; this method should be carried out 15 days before planting; or use Lvheng No. 1 4000-fold solution plus the usual amount of thiram, and spray the seedlings and soil when lilies emerge.
4.3 Seed bulb treatment: Before planting, carefully select seed bulbs, peel off the diseased scales, and then soak them in a prepared medicinal solution for sterilization. Specific method: soak the seed bulbs in a 50-fold solution of 40% formaldehyde for 15 minutes, rinse once with clean water, and then sow. Or soak in a 500-fold solution of 80% anthracnose thiram for 10 minutes or a 1000-fold solution of 70% thiophanate-methyl for 10 minutes, rinse with clean water and sow immediately. Treated seed bulbs must not be piled up, kept sealed or stored.
4.4 Field control: In the early stage of disease in the field, spray with a 500-fold solution of 80% anthracnose thiram, or a 1000-fold solution of 70% thiophanate-methyl, or a 600-fold solution of 75% chlorothalonil, or Lvheng No. 1 4000-fold solution plus the usual amount of thiram, once every 5-7 days, for 2-3 consecutive sprays. Several fungicides can be used alternately for better results.