Damping off is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions.
Symptoms
There are various symptoms associated with damping off; these reflect the variety of different pathogenic organisms which can cause the condition. However, all symptoms result in the death of at least some seedlings in any given population. Groups of seedlings may die in roughly circular patches, the seedlings sometimes having stem lesions at ground level. Stems of seedlings may also become thin and tough resulting in reduced seedling vigor. Leaf spotting sometimes accompanies other symptoms, as does a grey mold growth on stems and leaves. Roots sometimes rot completely or back to just discolored stumps.
Causal agents
A number of different fungi and fungi-like organisms cause the symptoms of damping off, including:
Alternaria species. Cause leaf spotting.
Botrytis cinerea also known as "grey mould". Symptoms caused by this often accompany other symptoms.
Fusarium species.
Macrophomina phaseoli a plant pathogen that causes charcoal rot on many plant species including Zea mays and Pinus elliottii.
Phyllosticta species. Cause leaf spotting.
Phytophthoraa genus of plant-damaging oomycetes, whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems.
Pseudomonas species. Cause leaf spotting.
Pythium a genus of parasitic oomycete. Once classified as fungi, and consequently sometimes still treated as such. Along with Rhizoctonia solani, attacks by Pythium are most associated with producing roughly circular patches of dead seedlings.
Thielaviopsis a small genus of fungi in the orderMicroascales. The genus includes several important agricultural pathogens.
Prevention
Damping off can be prevented or controlled in several different ways. Sowing seeds in a sterilized growing medium can be effective, although fungal spores may still be introduced to the medium, either on the seeds themselves or after sowing. To reduce survival of the pathogens, remove and discard diseased plants, and sterilize containers to remove dust, planting medium, and soil particles in which spores can survive. Maintaining drier conditions with better air circulation helps prevent the spread of the disease, although it can also prevent or slow down germination. Spraying or drenching the soil with a recommended anti-fungal treatment also helps suppress the disease. Homemade solutions are used by some gardeners for this purpose. In the UK, a copper-based fungicide called Cheshunt compound was widely used by amateur and professional gardeners against damping off, but it was withdrawn from sale in the UK in November 2010. Developed at an Agricultural Research CouncilExperimental Station in Cheshunt, Hertfordshire, UK, it was a mixture of copper sulfate and ammonium carbonate, which could be mixed by the gardener or bought ready-prepared.
