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What are the control methods for carnation wilt

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Wilt is caused by infection with a bacterium. The top of the diseased plant or a few branches wilt, and individual diseased plants suddenly wilt entirely, the diseased branches dry out and turn grayish green, later becoming yellowish brown to dark brown. After seedlings are infected, the leaves twist to one side and become deformed, and the roots become soft-rotted and brown. Under the microscope
Wilt is caused by infection with a bacterium. The top of the diseased plant or a few branches wilt, and individual diseased plants suddenly wilt entirely, the diseased branches dry out and turn grayish green, later becoming yellowish brown to dark brown. After seedlings are infected, the leaves twist to one side and become deformed, and the roots become soft-rotted and brown. Under the microscope, large numbers of bacteria ooze out from the diseased tissue (Figure 27). The pathogen comes from decayed residual roots and dead branches. Therefore, to control this disease, choose disease-free cuttings for propagation; do not damage the roots when transplanting, the soil should not be too wet, and avoid invasion and damage by the bacteria.

Control measures for carnation wilt

1. Distribution and damage

    Wilt is a common and serious disease of carnation. It occurs in Shanghai, Tianjin, Guangzhou, Hangzhou and other cities in China, and except in Hangzhou, the damage is relatively serious in the other cities. The disease damages many species of Dianthus plants such as carnation, Chinese pink and sweet William, causing the plants to wilt and die.

    2. Symptoms

    Plants can be affected at any stage of growth and development. First the lower leaves and branches of the plant become discolored and wilt, and this spreads rapidly upward; the leaves change from normal dark green to light green, and finally become a pale straw color. The plant wilts; sometimes when one side of the plant or half of an individual leaf is infected, it shows as one side of the branches and leaves or half of a leaf being visibly wilted; young shoots grow twisted, deformed and with arrested growth; young plants infected rapidly die. When a diseased stem is cut lengthwise, dark brown streaks can be seen in the vascular bundles, and from the cross-section an obvious dark brown ring pattern is visible. After the roots are infected, the infection spreads rapidly to the stem, and the plant finally wilts and dies.

    3. Pathogen

    The pathogen of wilt is Fusarium oxysporum f. sp. dianthi Sny et Hans, belonging to the Deuteromycotina, Hyphomycetes, Tuberculariales, Fusarium. It is the pathogen that specifically causes vascular bundle disease in carnation. The pathogen generally produces sporodochia, and there are two types of conidia, namely macroconidia and microconidia. Macroconidia are relatively stout, composed of several cells, slightly curved, sometimes sickle-shaped, with a slightly pointed tip, and relatively thin spore walls; microconidia are smaller, oval to oblong, with 1-2 cells. When the environment is unfavorable, dying plant tissue and diseased residues in the soil can produce large numbers of chlamydospores, which are smaller, round, thick-walled spores. According to a report by South China Agricultural University, the pathogen damaging Dianthus in Guangzhou is Fusarium dianthi (F. dianth pr-ill et Del), while Professor Wei Jingchao in China designated the Chinese name of this fungus as Fusarium oxysporum f. sp. dianthi. It causes carnation wilt. The fungal stroma is spreading type, pale to purplish red; macroconidia are stout, sickle-shaped, with one end relatively straight and one end slightly curved, 3-5 septa, colorless. Macroconidia with 3 septa measure 25-34.5μm×3.8-4μm, and macroconidia with 5 septa measure 44×4.3μm; microconidia are single-celled, colorless, oval or elliptical, measuring 5-9μm×2-4μm; chlamydospores are spherical, 6-11μm in diameter, terminal or intercalary; they can produce sclerotia, 0.5-2.0mm or 3-12mm in diameter.

    According to a report by Professor Yu Dafu: the Fusarium species on carnation in China also include three species: Fusarium poae (Peck) Wr., Fusarium avenaceum (Fr.) Sacc. and Fusarium culmorum (W.G.Sm.) Sacc. They respectively cause flower rot, root rot and stem rot of carnation. Fusarium poae currently causes relatively serious damage on Dianthus in Guilin, China.

    4. Disease development pattern

    The pathogen survives in diseased plant residues or in the soil. In humid environments, the decayed areas of diseased roots or stems produce fruiting bodies, and the spores are spread by air currents or by splashing of rain and irrigation water; they invade and cause damage through wounds on the roots and stem base or on cuttings, and the pathogen enters the vascular bundle system and gradually spreads upward. The pathogen may colonize the vascular bundle system without showing symptoms. Studies on the spread of the pathogen within the host show that before symptoms appear, the pathogen spreads relatively slowly within the vascular bundles, but some propagation materials obtained from infected mother plants may carry latent infection. Therefore, propagation materials are an important source of disease spread, and contaminated soil is also one of the sources of spread. Generally in spring and summer, if the soil temperature is relatively high, with continuous overcast and rainy weather, and under conditions of waterlogged soil, the disease occurs severely. Excessive application of nitrogen fertilizer during cultivation, as well as acidic soil, are both favorable to the growth and infection of the pathogen and promote the occurrence and epidemic of the disease. In the Guangzhou area, wilt often occurs from April to June.

    5. Control measures

    Cuttings should be taken from healthy, disease-free mother plants, and it is best to establish a disease-free mother stock area for collecting cuttings.

    When diseased plants are found, remove and destroy them promptly to reduce the accumulation of the pathogen in the soil.

    Soil treatment: If the soil of the nursery area or the potting soil is contaminated, it must be replaced or disinfected before use. Where conditions permit, greenhouses can be sterilized with steam; abroad, soil has been fumigated and disinfected with metham sodium, methyl bromide, etc.; watering the soil before planting with 50% captan or 50% carbendazim at 500 times dilution, or 70% dexon at 500 times dilution, or treating the soil with 3% ferrous sulfate all have control effects.

    Biological control is a promising measure. In recent years there have been many reports abroad. For example, in the United States, before planting, Metz high-quality sandy fertile mud is applied into the soil at 600g/m2, which can control the occurrence of carnation wilt. According to research, this fine sandy fertile mud contains a type of Pseudomonas putida (Trevisan) Migula, which has an antagonistic effect on the pathogen and competes with it for iron, thereby achieving the purpose of disease prevention. Another method is to treat the soil with a type of bacterium (Chitinolytic sp.), which can reduce the impact of the disease.

    In addition, there is a type of Phialophora cinerescens that likewise causes carnation wilt. This fungus invades the plant through wounds, fine root tips and root hairs, enters the vessels, and obstructs water transport. The toxins produced by the pathogen also damage the living tissues of the host, causing the plant to wilt. The affected tissue turns brown, and there is no clear boundary between diseased and healthy tissue. Plants can be infected at different stages of development. For control measures, refer to Fusarium wilt of carnation..

Symptoms and control of carnation wilt

        1. Distribution and damage Wilt is a common and serious disease of carnation. It occurs in Shanghai, Tianjin, Guangzhou, Hangzhou and other cities in China, and except in Hangzhou, the damage is relatively serious in the other cities. The disease damages many species of Dianthus plants such as carnation, Chinese pink and sweet William, causing the plants to wilt and die.

2. Symptoms Plants can be affected at any stage of growth and development. First the lower leaves and branches of the plant become discolored and wilt, and this spreads rapidly upward; the leaves change from normal dark green to light green, and finally become a pale straw color. The plant wilts; sometimes when one side of the plant or half of an individual leaf is infected, it shows as one side of the branches and leaves or half of a leaf being visibly wilted; young shoots grow twisted, deformed and with arrested growth; young plants infected rapidly die. When a diseased stem is cut lengthwise, dark brown streaks can be seen in the vascular bundles, and from the cross-section an obvious dark brown ring pattern is visible. After the roots are infected, the infection spreads rapidly to the stem, and the plant finally wilts and dies.

3. Pathogen The pathogen of wilt is Fusarium oxysporum f. sp. dianthi Sny et Hans, belonging to the Deuteromycotina, Hyphomycetes, Tuberculariales, Fusarium. It is the pathogen that specifically causes vascular bundle disease in carnation. The pathogen generally produces sporodochia, and there are two types of conidia, namely macroconidia and microconidia. Macroconidia are relatively stout, composed of several cells, slightly curved, sometimes sickle-shaped, with a slightly pointed tip, and relatively thin spore walls; microconidia are smaller, oval to oblong, with 1-2 cells. When the environment is unfavorable, dying plant tissue and diseased residues in the soil can produce large numbers of chlamydospores, which are smaller, round, thick-walled spores. According to a report by South China Agricultural University, the pathogen damaging Dianthus in Guangzhou is Fusarium dianthi (F. dianth pr-ill et Del), while Professor Wei Jingchao in China designated the Chinese name of this fungus as Fusarium oxysporum f. sp. dianthi. It causes carnation wilt. The fungal stroma is spreading type, pale to purplish red; macroconidia are stout, sickle-shaped, with one end relatively straight and one end slightly curved, 3-5 septa, colorless. Macroconidia with 3 septa measure 25-34.5μm×3.8-4μm, and macroconidia with 5 septa measure 44×4.3μm; microconidia are single-celled, colorless, oval or elliptical, measuring 5-9μm×2-4μm; chlamydospores are spherical, 6-11μm in diameter, terminal or intercalary; they can produce sclerotia, 0.5-2.0mm or 3-12mm in diameter.

According to a report by Professor Yu Dafu: the Fusarium species on carnation in China also include three species: Fusarium poae (Peck) Wr., Fusarium avenaceum (Fr.) Sacc. and Fusarium culmorum (W.G.Sm.) Sacc. They respectively cause flower rot, root rot and stem rot of carnation. Fusarium poae currently causes relatively serious damage on Dianthus in Guilin, China.

4. Disease development pattern The pathogen survives in diseased plant residues or in the soil. In humid environments, the decayed areas of diseased roots or stems produce fruiting bodies, and the spores are spread by air currents or by splashing of rain and irrigation water; they invade and cause damage through wounds on the roots and stem base or on cuttings, and the pathogen enters the vascular bundle system and gradually spreads upward. The pathogen may colonize the vascular bundle system without showing symptoms. Studies on the spread of the pathogen within the host show that before symptoms appear, the pathogen spreads relatively slowly within the vascular bundles, but some propagation materials obtained from infected mother plants may carry latent infection. Therefore, propagation materials are an important source of disease spread, and contaminated soil is also one of the sources of spread. Generally in spring and summer, if the soil temperature is relatively high, with continuous overcast and rainy weather, and under conditions of waterlogged soil, the disease occurs severely. Excessive application of nitrogen fertilizer during cultivation, as well as acidic soil, are both favorable to the growth and infection of the pathogen and promote the occurrence and epidemic of the disease. In the Guangzhou area, wilt often occurs from April to June.

5. Control measures Cuttings should be taken from healthy, disease-free mother plants, and it is best to establish a disease-free mother stock area for collecting cuttings.

When diseased plants are found, remove and destroy them promptly to reduce the accumulation of the pathogen in the soil.

Soil treatment: If the soil of the nursery area or the potting soil is contaminated, it must be replaced or disinfected before use. Where conditions permit, greenhouses can be sterilized with steam; abroad, soil has been fumigated and disinfected with metham sodium, methyl bromide, etc.; watering the soil before planting with 50% captan or 50% carbendazim at 500 times dilution, or 70% dexon at 500 times dilution, or treating the soil with 3% ferrous sulfate all have control effects.

Biological control is a promising measure. In recent years there have been many reports abroad. For example, in the United States, before planting, Metz high-quality sandy fertile mud is applied into the soil at 600g/m2, which can control the occurrence of carnation wilt. According to research, this fine sandy fertile mud contains a type of Pseudomonas putida (Trevisan) Migula, which has an antagonistic effect on the pathogen and competes with it for iron, thereby achieving the purpose of disease prevention. Another method is to treat the soil with a type of bacterium (Chitinolytic sp.), which can reduce the impact of the disease.

In addition, there is a type of Phialophora cinerescens that likewise causes carnation wilt. This fungus invades the plant through wounds, fine root tips and root hairs, enters the vessels, and obstructs water transport. The toxins produced by the pathogen also damage the living tissues of the host, causing the plant to wilt. The affected tissue turns brown, and there is no clear boundary between diseased and healthy tissue. Plants can be infected at different stages of development. For control measures, refer to Fusarium wilt of carnation.

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