Serenade ASO, based on a strain of Bacillus subtilis, is produced by US firm AgraQuest and marketed in the UK by Fargro in conjunction with Syngenta Bioline.
Fargro managing director Dr Paul Sopp said: "The big advantage of Serenade is that it leaves absolutely no residue. Initially, we see it being used close to harvest and during picking as it has no harvest interval. But once we get more experience with it, we would expect it to be used earlier in the season as part of a rotation with conventional fungicides."
He explained that the bacteria is actually living and multiplies on the fruit and foliage. It produces lipopeptides (a form of fat-containing protein) that attacks Botrytis spores and mycelium and also stimulates the plant's own defence mechanism.
"In addition, the bacteria provide a physical barrier (to infection) on flowers, for example, where Botrytis gets in," said Sopp. "However, this is a less important mode of action than the others."
Serenade is mostly a preventative product but it does have some curative activity, he added. There is good evidence from the 30 or so countries where it has been registered for some time - including a number in mainland Europe - that it also controls other diseases such as powdery mildew, anthracnose and even scab.
It is compatible with commonly used biological pest control agents and conventional fungicides, and their cost is comparable.
Serenade's label states that it can be used up to 20 times per season, applied at 10 litres/ha at seven-day intervals. Fargro hopes to get specific off-label approvals for its use on other crops prone to Botrytis attack, like raspberries.
The company has also requested Serenade's approval as an organic fungicide from the Soil Association.