Common diseases of Cosmos and their prevention and control methods

Common diseases of Cosmos: leaf spot

Symptoms

There are oval and long light reddish-brown spots on the leaves, surrounded by chlorotic circles, which later expand into large irregular patches with black spots on them.

Prevention and treatment methods

Remove diseased leaves and spray pesticides in time. It can be sprayed with 500 times diluted 50% thiophanate wettable powder.

Common diseases of cosmos: powdery mildew

Symptoms

The diseased parts are leaves, young stems, flower buds and flower buds, etc. The obvious feature is the presence of a grayish-white powdery mold layer (conidia and mycelium of the pathogen) on the diseased area. The growth and development of the affected plants are stunted, the leaves are twisted, and they cannot bloom or the flowers become deformed. When the disease is severe, the leaves dry up and the plant dies.

Pathogen analysis

The pathogen of powdery mildew is Erysiphe graminis, which belongs to the subphylum Ascomycota. Mycelium grows on both sides of the leaves, conidia are columnar, ascocarps are aggregated or nearly aggregated, dark brown, oblate, accessory filaments are unbranched or irregularly branched, curved, asci are long or short ovate, and ascospores are oval or elliptical.

Prevention and treatment methods

Apply more phosphorus and potassium fertilizers appropriately, and pay attention to ventilation and light transmission.

Prune off seriously diseased plants or seriously diseased parts promptly, bury them deeply or burn them to eliminate the source of bacteria.

If necessary, spray 1500 times diluted 15% triadimefon wettable powder at the early stage of the disease.

Common diseases of Cosmos: Botrytis cinerea

Symptoms

The seedlings infected with gray mold are light in color, and the leaves and petioles are grayish white and water-soaked. The tissues soften and rot, and gray mold grows on the surface when the humidity is high.

Young stems often initially develop irregular water-soaked spots at the base of the petiole, which quickly become soft and rotten, and then shrink or break. Finally, the diseased seedlings rot, wither and die.