How to prevent and control powdery mildew in pot marigold

Affected plant: pot marigold (Calendula officinalis L.).

Distribution and damage: The disease occurs commonly in Hebei, Liaoning, Yunnan and other places, and causes relatively serious damage.

Symptoms: After the leaves and stems are infected, powdery round spots 0.5-1.2 mm appear on the leaves, distributed irregularly, later spreading over the entire leaf, covering the leaf surface with a layer of white powder. The stems are also covered with white powder. Severely affected plants have yellowing stems and leaves, and may even wither and die.

Pathogen: The pathogen is Erysiphe cichoracearum. The mycelium generally grows on both sides of the leaf, and in a few cases on the underside. Conidia are barrel-shaped to cylindrical. Cleistothecia are oblate, dark brown. They are clustered to nearly scattered, with irregular, polygonal wall cells. There are ii-85 appendages, mostly 18-40, generally unbranched, mostly uneven in thickness, septate, dark brown. Asci are oval, rectangular to elliptical, 5-24, mostly 10-20, stalked or a few nearly sessile. Ascospores are oval, oblong to oval, yellowish, generally 2-3, rarely 4.

Disease development: The pathogen overwinters as cleistothecia (closed fruiting bodies) or mycelium in diseased tissues. Ascospores and conidia are mainly spread by wind and rain. The disease is severe when the climate is dry and the temperature is 17-25°C.

Control methods: Diseased plants should be pulled up and burned in a centralized manner to reduce sources of infection. Strengthen management, pay attention to ventilation and light transmission, apply less nitrogen fertilizer, apply more phosphorus and potassium fertilizer, and control humidity. Do not plant too densely. In the early stage of the disease, use 15% triadimefon wettable powder at 800-1000 times dilution, or 20% antimycin at 120 times dilution, or 50% sulfur suspension concentrate at 300 times dilution.

Damage symptoms of pot marigold

Control methods for powdery mildew of pot marigold

I. Damage symptoms:Round white powdery spots first appear on the leaf surface. After expansion, both sides of the leaves and the stems are covered with a grayish-white powdery layer. Later, sparse dark brown small dots, the pathogen's cleistothecia, appear on the diseased parts. In severe cases, plant growth stops, and the leaves turn yellow and dry up.

II. Morphological characteristics of the pathogen:The pathogen is Erysiphe cichoracearum DC., an ascomycete fungus. The mycelium creeps on both sides of the host leaves and extends haustoria into epidermal cells to absorb nutrients. Short stalks grow from the mycelium, and conidia are produced in chains at the ends of the stalks. The conidia are elliptical, 30-40 X 18-25 (um). Later, sparse dark brown small dots, the pathogen's cleistothecia, appear on the diseased parts. The cleistothecia are 85-114 um in diameter, bear appendages on the surface, and contain 6-21 asci. The asci are elliptical, 44-107 X 23-59 (um), and contain 2 ascospores, 19-38 X 11-22 (um).

III. Disease characteristics:In the south, it can occur all year round with no obvious overwintering period. It is prone to occur in early spring in February and March when it is warm and humid, with heavy fog or heavy dew. In cold northern regions, it overwinters as cleistothecia with diseased residues on the soil surface. When conditions are suitable the following year, ascospores are produced for primary infection, and conidia produced on the lesions are spread by airflow for secondary infection.

IV. Epidemic dynamics:In production, insufficient soil fertility or excessive application of nitrogen fertilizer, shading between plants, and poor drainage make this disease likely to occur.

V. Control methods:

(1) Provide careful maintenance, pay attention to clearing ditches and draining water to reduce field humidity. Apply more phosphorus and potassium fertilizer, and avoid excessive nitrogen fertilizer or fertilizer deficiency.

(2) In the early stage of the disease, promptly spray 25% triadimefon wettable powder at 1000-1500 times dilution or 50% sulfur suspension concentrate at 300 times dilution. In addition, 2% agricultural antibiotic 120 aqueous solution or wuyiencin (Bo-10) at 150-200 times dilution can also be sprayed, once every 10-15 days depending on the disease severity, for a total of 2-3 treatments.

(3) In areas with severe disease or where resistance has developed, 40% flusilazole emulsifiable concentrate at 7000 times dilution can be used instead, with a long duration of effect and excellent control efficacy.

VI. Commonly used pesticides:25% triadimefon wettable powder, 50% sulfur suspension concentrate, 2% agricultural antibiotic 120 aqueous solution, 40% flusilazole emulsifiable concentrate

Powdery mildew of pot marigold

[Distribution] Hebei, Liaoning, Beijing, Shanghai, Jiangsu and other places.

[Symptoms] Both leaves and stems can be affected. In the early stage, white powdery round spots appear on both the front and back sides of the leaves; after the disease expands, the leaf surface is covered with a layer of white powder, and the stems are also covered with a layer of white powder; later, sparse dark brown small dots, the pathogen's cleistothecia, appear on the diseased parts. In severe cases, plant growth stops, and the leaves turn yellow and dry up.

[Pathogen]  The pathogen is a fungus, Erysiphe cichoracearum. The pathogen's cleistothecia are oblate. The mycelium creeps on both sides of the host leaves and extends haustoria into epidermal cells to absorb nutrients. Short stalks grow from the mycelium, and conidia are produced in chains at the ends of the stalks. The conidia are elliptical, 30-40 X 18-25 (um). Later, sparse dark brown small dots, the pathogen's cleistothecia, appear on the diseased parts. The cleistothecia are 85-114 um in diameter, bear appendages on the surface, and contain 6-21 asci. The asci are elliptical, 44-107 X 23-59 (um), and contain 2 ascospores, 19-38 X 11-22 (um). Only conidia have been observed in Shanghai.

[Disease characteristics] The pathogen overwinters as cleistothecia or mycelium in the diseased tissues of affected leaves and stems. The pathogen is mainly spread by wind and rain. When the temperature is 17-25°C and the climate is dry, the disease is severe. In the south, it can occur all year round with no obvious overwintering period. It is prone to occur in early spring in February and March when it is warm and humid, with heavy fog or heavy dew. In cold northern regions, it overwinters as cleistothecia with diseased residues on the soil surface. When conditions are suitable the following year, ascospores are produced for primary infection, and conidia produced on the lesions are spread by airflow for secondary infection.

[Disease pattern] The pathogen overwinters as cleistothecia or mycelium on the diseased tissues of stems and leaves; the pathogen has a wide host range and can damage other Asteraceae flowers.

[Epidemic dynamics] In production, insufficient soil fertility or excessive application of nitrogen fertilizer, shading between plants, and poor drainage make this disease likely to occur.

[Control methods]

   (1) Horticultural control: Provide careful maintenance, pay attention to clearing ditches and draining water to reduce field humidity. Apply more phosphorus and potassium fertilizer, and avoid excessive nitrogen fertilizer or fertilizer deficiency. Remove the pathogen and do not practice continuous cropping.

   (2) Chemical control: Choose 70% thiophanate-methyl at 1500 times dilution, or 20% triadimefon at 3000 times dilution, or 12.5% diniconazole at 3000 times dilution, spraying once every 10-15 days for 2-3 consecutive sprays. Or spray 20% antimycin at 100-200 times dilution. In the early stage of the disease, promptly spray 25% triadimefon wettable powder at 1000-1500 times dilution or 50% sulfur suspension concentrate at 300 times dilution. In addition, 2% agricultural antibiotic 120 aqueous solution or wuyiencin (Bo-10) at 150-200 times dilution can also be sprayed, once every 10-15 days depending on the disease severity, for a total of 2-3 treatments. In areas with severe disease or where resistance has developed, 40% flusilazole emulsifiable concentrate at 7000 times dilution can be used instead, with a long duration of effect and excellent control efficacy.