Marlborough wine growers facing botrytis challenge

Many grape blocks in Marlborough are carrying high levels of botrytis, with harvest still a month away for some.

HortResearch scientist Rob Agnew said the region was probably having its worst botrytis year since 1996, with some blocks carrying more bunches with the fungus than without.

Botrytis cinerea is a vineyard fungus that can infect berries in wet, warm weather, causing rot disease and affecting juice quality.

It can be regarded as a good fungus, producing "noble rot" if it attacks ripe, healthy grapes in the right weather, causing the berries to shrivel into raisins and concentrate their juice and grape sugars.

But more commonly, the berries fail to dry out, and bunch rot occurs, in which other fungi, yeasts and vinegar bacteria invade. Fungi such as penicillium, aspergillus and mucor cause some nasty flavours.

Mr Agnew said there had been a large infection period two weeks ago and one at the end of January and beginning of February. The grey, wet weather in the past few days would certainly have aggravated the situation, he said.

"We would expect to see the botrytis spreading quite a bit in the next few days."

In the past week he had seen 20 to 30 per cent of bunches infected by botrytis in some blocks "and some blocks have much more than that".

"Everyone will have some botrytis and some blocks have already got a surprisingly high amount."

Growers with bunches that would not be harvested for another month would face the greatest botrytis challenge, he said.

It was possible some people would not harvest if a large proportion of their crop was affected by botrytis, but the main impact would be that high levels of botrytis would affect fruit and subsequently wine quality.

Many wine companies will have penalty clauses in their contracts, meaning a grower with too much botrytis will get penalised.

Mr Agnew said that since 1995, which was considered "a year from hell", and 1996, which also had a "reasonable amount of botrytis", growers had received a really good run of seasons for botrytis.

"It is different from most challenging botrytis years that growers have faced since the mid to late 90s."

Last year the botrytis did not hit until the end of March, but this year, with a much higher crop load that would take longer to mature, the risk was far higher. The bigger crops would pay the bigger price.

"If your crop is going to be there later then it has got more time to be infected and more time for the botrytis to spread.

"Once you have got botrytis in the bunch it is very difficult to get rid of it at this stage in the season.

"I would say you probably won't."

Marlborough Winegrowers spokesman Stuart Smith said this year was the first time growers had faced a botrytis challenge for a number of years.

But they were better armed with chemicals to deal with the fungus now, he said.

The wet, grey weather this season was not typical of Marlborough, but growers had had good weather in December and January.

Montana viticulturist Mike Insley said there was some botrytis in the region, but he did not consider it to be any worse than previous seasons.

Villa Maria viticulturist Anton Rasmussen said good canopy management after recent rain fall had allowed more air movement through the vines and reduced botrytis infection to quite low levels.

The noble rot

* Botrytis blight or gray mould affects a wide range of grape varieties.

* A fungal disease, it causes infected grapes to dry and shrivel.

* If it attacks ripe, healthy grapes it can leave their flavours concentrated and produce stunning wines - hence the noble rot.


- NZPA