Our grape growing weather obsession is in high gear at the moment as we head toward the hotter months of the year. It’s been a great start to the season, with generally mild to warm weather and not too much rain north of Auckland at this stage. NIWA says that we are currently experiencing moderate La Niña conditions through to mid-2021. La Niña is one extreme of the phenomenon called The Southern Oscillation, the other extreme being El Niño.
This is great news for grapegrowers at the moment, and also the population in general, as La Niña will bring warmer than average sea temperatures and a warmer than average summer for most of the North Island. What does worry us as grapegrowers is the increased chance of a tropical cyclone or two brushing past us and dumping a large amount of rain between February and April. One big rain event might be okay, but two in the space of two or three weeks can spell disaster for our crop. Once the ground is wet, the vines will suck up the moisture, causing berries to bulge and split and mould to grow.
There are a few things we can do to try to mitigate the adverse effects of rain. We can spray fungicides to stop the mould and mildew growing, which we already do, but we are increasingly aware of trying to minimise chemical use in the way we do things, especially close to harvest. Once I knew that there was an increased risk of La Niña, I began an extensive regime of extra shoot thinning in our vines to try to open up the canopy and allow more air through them to keep them drier. This will decrease the amount of grapes available to harvest, which most growers will do anyway to increase quality.
There are some varieties of grapes that are better suited to handling wet conditions and the extra water that can be sucked up during a rain event. Albarino grapes have quite thick skins and are less likely to split under pressure after a rain event. Syrah and verdelho bunches are quite loose, which means they are less likely to hold moisture inside the bunch if some of their berries do split. Pinot gris, on the other hand, has thinner skin and very small tight bunches, so a number of heavy rain events close together can nearly wipe out a harvest. So, we are in the hands of Mother Nature; maybe luck will be on our side this year.
Richard Robson, Matakana Winegrowers