Control botrytis with ozone

BOTRYTIS CINEREA THREATENS WHAT THE RAND PROVIDES

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Recent rand strength does not distract from the basic fact that one unit of European currency is traded for 15 of ours. This currency bonanza has led to a surge in South African table grape exports. For example, exports of seedless grapes increased to 482 million cartons in 2014 compared with 195 million cartons in 2010, according to the SA Table Grape Industry.

 

Unfortunately – and as all farmers know – there’s a menacing cloud in every silver lining. For local table grape exporters that cloud is the plant pathagen, ‘Botrytis Cinerea’, the cause of grey mould. This is the most important post harvest disease of table grapes and the bane of fruit exporters everywhere. There is a way however to remove the fear of the necrotrophic fungus in grape transport and storage.

 

A grower of organic table grapes for local and overseas consumption, would be keen to reduce fungal decay and fungicide residue on naturally grown produce by using an organic technology. Natural ozone gas can be used to keep Botrytis Cinerea in storage and transport.

 

In the industry it is well known that sulphur is the accepted way to control botrytis. During warehouse cold storage of harvested table grapes, they are usually subjected to an initial fumigation with SO2 during forced air cooling within hours of harvest. This is followed one week later by a two to six hour long SO2 fumigation that is repeated weekly during cold storage.

 

Sulphur works. It is an effective means to control the decay of table grapes, but there are significant health issues associated with sulphur residues, emissions, and it has a negative impact on grape berry quality. However the standout issue is that the use of sulphur on export grapes can result in a non-organic classification by European authorities. In South Africa, sulphur is also an issue as its use is prohibited on certified organic grapes.

 

Fortunately for organic farmers ,ozone is recognised as an acceptable technology to use with grapes marketed under the organic classification. The O3 gas does not harm the grapes and reduces the number of decayed berries. It does not significantly alter berry appearance and there are fewer bleaching injuries to the berries which are commonly associated with sulphur dioxide.

 

Ozone treatment is an organic option that works extremely well. After packaging, the grapes are stored in a cold room where specified amounts of ozone gas are introduced. The grapes are again exposed in refrigerated shipping containers to ozone gas for the duration of the voyage to Europe says one exporter. ” We love the fact that ozone fumigation does not require further manual handling of our beautiful produce,” concludes the farmer.

 

Ozone is a pesticide-residue free treatment allowed as ‘organic’ by the US National Organic Program. Fumigation with ozone gas during pre-cooling of grapes controls postharvest decay and reduces residues of commonly used fungicides.