WINEMAKERS are watching the temperature gauge with concern.

More temperatures in the 40s for an extended period, could be devastating on the 2010 harvest.

What would devastate crops is if severe thunderstorms, mixed with even a little hail, dropped on the vineyard areas during a heatwave.

The wind and temperatures in the 40s last Friday did not have a major affect on the conditions of vines, but those areas that did experience hail had their crops impacted.

Catherine Vale Vineyard owner Wendy Lawson said if the recent heat had occurred after the grapes were in the colouring stage, or verasion stage, the impact would have been worse.

“When the temperature reaches over 36 degrees, the vines shut down and stop photosynthesis, which protects them from major damage,” she said.

“If this happens for a long period though, there can be cause for concern.

“Ideal conditions at the moment would be day temperatures of around 32-34 degrees and night temperatures below 20.”

Conditions are still very dry though and the focus at the moment is on keeping moisture up to the plants.

“At the moment we are irrigating every two days for three hours and testing the levels to make sure the moisture is getting to the plant and not causing any problems with root rot,” Mrs Lawson explained.

“One of the beauties of the Hunter Valley is that there are so many different soil conditions throughout the area and each vineyard has to adapt to their own conditions.”

At this stage there is no concern about disease and Mrs Lawson said it would only be a wet period that would put vineyards under powdery mildew pressure.

The predictions for 2010 are looking good and Mrs Lawson said the vineyards are looking great with high yields looking probable.

“We have the biggest canopy in some varieties that we have ever had since our first vintage in 1997,” she added.

If conditions are ideal harvest for sparkling wines will begin in the early weeks of January and varieties such as Semillon and Verdelho coming off in the middle of the month.