Science Into Practice - Fighting Botrytis in glasshouse tomato crops

The suppression and control of high humidity in glasshouses is important because it helps prevent fungal disease and promotes crop transpiration and growth. Condensation or relative humidities of more than 90 per cent for prolonged periods increase the risk of stem Botrytis, a devastating disease in glasshouse tomato crops.

Condensation occurs when air is cooled below its dew point, causing water vapour to be released as a liquid and deposited on cool surfaces. Humidity control systems used in glasshouses are mainly based on air-humidity sensing equipment. This does not always avoid condensation on plant foliage because it fails to consider the dew point and the micro environment at the plant/air interface. It also fails to recognise differences in conditions along horizontal and vertical planes.

Growers therefore set humidity controls lower (below 85-90 per cent) than necessary to prevent general condensation. Tomato Botrytis continues to be reported, despite growers employing such strategies.

Tim Pratt of Farm Energy and Tim O'Neill of ADAS set out to investigate whether direct stem temperature measurements could be used to prevent condensation, thereby reducing the risk of Botrytis, in HDC project PC 301. Condensation events at various stem heights were monitored on five commercial nurseries.

No stem condensation was recorded at four sites and only rarely at the fifth, but varying Botrytis levels occurred at three. The researchers concluded that condensation is not a prerequisite for Botrytis. Nevertheless, the study highlighted that stem temperature sensors could be used to fine-tune glasshouse humidity control, cutting energy costs.

Horticultural Development Company

For details on all HDC activity, visit www.hdc.org.uk


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