Growing advice - Damping off

Damping off is one of the most common and troublesome types of garden diseases. It can affect all types of seedlings, but is most problematic on fast growing flower seedlings such as antirrhinums, lobelias, nemesias, petunias, salvias and stocks or vegetable seedlings like cabbages, cress, lettuces, tomatoes, peas and beans. Some slow growing trees and shrubs are also very prone to grey mould forms of damping off.

Symptoms are varied but all result in seedling death. Often young seedlings rapidly collapse in small roughly circular patches, or the seedlings may become weak looking and have shrivelled stems, sometimes the root system simply rot away. Some larger seedlings or young plants also sometimes show leaf spotting or other discoloration, some even show grey mould on the stems or leaves.

Organisms that cause damping off symptoms are varied. The most common ones that cause dying out in patches are the fungi Pythium and Rhizoctonia solani, surviving as spores in the soil. Stem lesions are often caused by soil-borne species of Alternaria and leaf spots are generally associated with soil-borne Phyllosticta and Pseudomonas fungi. The grey mould that often accompanies damping off is caused by Botrytis cinerea.

Treatment is difficult in the garden environment. Some chemical controls have been employed in commercial practices, but are not yet available for use on a small scale. For the amateur or small-scale grower hygiene at all stages of propagation is essential. Only use cleaned and disinfected pots and seed trays and make sure that greenhouse benches are sterile. Mains water and a proprietary sterilised seed compost, which is moist but not over wet, should also be used. Don't assume all bought compost is sterile, as most is not.

Small quantities of compost for seed sowing can be sterilised by 'cooking' in an oven at 150C for an hour or so. Care should be taken when using water other than tap water. All storage tanks should be regularly cleaned and disinfected regularly, preference should always be given to tap water on susceptible plants.

Avoid stressing plants and seedlings by preventing waterlogging and high humidity, as this will make them more vulnerable and prone to attack. Sow seed thinly and prick out as soon as possible, handling the seedlings by their leaves, not stems. Do not re-use compost that has been affected and if only part of the seed tray has shown symptoms remove all the affected seedlings, a few extra seedlings and the affected compost. Water with Cheshunt Compound or similar fungicide to help prevent any spread. Cheshunt Compound can also be used as a soil drench prior to seed sowing as a preventative measure, but this will not completely eradicate all problems. It should be used as a preventative aid.

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