How does garden balsam damping-off occur?
Garden balsam damping-off is widespread in China and is a common disease in garden balsam cultivation, causing serious damage. The disease mainly infects the root and stem base.
Symptoms: after the root and stem are affected, there is black constriction; when the environment is humid, white mold-like growth appears on the diseased part; the pathogen spreads rapidly and occurs severely, causing the upper leaves to wilt and dry up within a few days, and in severe cases the whole plant dies.
The pathogen Rhizoctonia solani Kuhn is called Rhizoctonia solani, a fungus of the Deuteromycotina. This fungus does not produce spores; after the hyphae grow for a certain time, they interweave to form sclerotia. The sclerotia are initially flat-round, later becoming irregular, relatively small, and light brown; when the sclerotia germinate, they produce hyphae. The sexual stage is uncommon; when humidity is high, a thin layer of grayish-brown fungal membrane, namely basidia and basidiospores, is produced on the surface of the diseased part of the stem and leaves near the soil surface. The basidia are colorless, club-shaped to barrel-shaped, with 4 sterigmata at the apex, and each sterigma bears 1 basidiospore; the basidiospores are single-celled, colorless, and obovate.
Disease characteristics: the pathogen mainly overwinters as mycelium or sclerotia in diseased residues or soil. The mycelium in the soil lives saprophytically and does not dormancy. When organs contact diseased soil, infection can occur; under conditions with a water film, healthy leaves in contact with the diseased part will become infected. In addition, seeds, farm tools and contaminated compost can spread the disease over long distances. The mycelium growth temperature is 6-40°C, and the optimum growth temperature is 20-30°C, especially 25-30°C, at which it grows fastest. The mycelium prefers cool, dry soil; under high-humidity conditions, generally at a relative humidity of 98%, the sclerotia can germinate and invade. Plants with weak resistance, soil temperature and humidity that are too high or too low, and relatively heavy soil are all favorable to disease development.
Control methods
(1) Agricultural control: strengthen cultivation management, apply fertilizer and water reasonably, regulate ventilation and light transmission, and improve plant resistance. Drain promptly after rain, maintain appropriate temperature and humidity, clear away diseased residues, and burn or destroy them collectively to reduce sources of infection.
(2) Improve heavy soil to reduce the occurrence of the disease.
(3) Choose relatively disease-resistant varieties.
(4) Chemical control: at the early stage of disease, spray 75% chlorothalonil wettable powder 600 times dilution, or 60% carbendazim•thiram wettable powder 500 times dilution, or 20% tolclofos-methyl emulsifiable concentrate 1200 times dilution.
Commonly used agents: chlorothalonil wettable powder, carbendazim•thiram wettable powder, tolclofos-methyl emulsifiable concentrate.