However, new vineyards are using steel posts for their trellising.
NZ Winegrowers GM sustainability Ed Massey says ‘‘if you’ve got a vineyard and you decide, ‘right, I’m going to transition to an organic vineyard’, you can do that with your existing trellising, if that’s CCA’’.
But for a new organic vineyard your posts have to be non-treated — for example, steel or plastic.
Ironically, Massey notes, wooden posts are ‘‘a great store of carbon’’.
‘‘And we know from working with Goldpine and other suppliers the processes they go through to ensure that treatment stays in the post has really improved substantially in the last two decades.’’
Local viticulturist Tim ‘Timbo’ Morrison-Deaker says ‘‘I’d suggest there’s probably more arsenic in a kilogram of prawns from Thailand’’.
He adds the schist-based soils Central Otago sits on have naturally-formed arsenic in them — ‘‘these wooden posts wouldn’t be adding any level to that’’.
He says steel posts, apart from removing any potential for copper-chromium-arsenic leaching, are also thinner, so they’re better for grape-growing.
However, industry experts agree there’s a disposal problem with treated timber posts.
Morrison-Deaker says on average 1.5% of posts are lost every year when a machine harvester goes through them.
‘‘And then you’ve got to work out how do you dispose of those arsenic-treated posts, because you don’t want them up in the landfill and you can’t burn them because that causes environmental issues.
‘‘Whereas, with steel posts, if they do break there’s actually a recyclable value to them.’’
Local vineyard owner Greg Hay says low rainfall also mitigates against any leaching from timber posts.
‘‘If there were toxic levels coming out of anything, the vines would show it, like they’d be sick.’’
However, he quips, he doesn’t think many vineyard owners would use the posts as their barbecue wood of choice.
- Philip Chandler
