By Max Marriott
Assistant Vineyard Manager, Vinewise Viticulture
The growing season leading up to harvest in Central Otago – like much of the country – was dry. Spectacular, but dry. Our irrigation stations at the School House vineyard were on 24/7 for several weeks during and after veraison, in a bid to keep up with demand. Fortunately, irrigation kept up with maintenance water supply. The conventional blocks were just as needy as the organic blocks; the issue wasn’t the narrow topsoil layer at the top, but the deeper subsoil layers that were struggling to hold and retain moisture.
Looking down the rows where the conventional/organic splits occur, the dramatic colour differences observed in the first year of organic conversion weren’t as obvious this time around. However, there were still vigour differences. The vigour is the number one difference that has occurred since transitioning our conventional blocks to organics. It’s at the top of the list in terms of our management priorities; so far, the level of vigour has been acceptable, albeit slowly declining in the organic blocks, and we’re now looking to halt that decline and slowly increase vigour.
There have been several reasons for this decline. The first and subsequent weeding passes have cut established vine roots, which are significant events in a vine’s life; like you and me, rehabilitation can be slow after you’ve had a leg cut off. The change in regime itself also takes a toll; when you’ve been fed junk food all your life, and then switch cold turkey to greens and lentils, there’s definitely a what-the-hell-is-this phase and some rebound time involved.The weed competition is also a factor. Now, this can be split into three categories. There is first the inter-vine weed cover, which is easily managed, though it does compete, no doubt about it. Then there are the grasses and legumes which seem to hug the trunks of the vines. Sometimes the blade catches these – especially when the wings are on – sometimes it doesn’t. Given the drippers are still placed directly next to the vines (we will transition them a third of the way along the inter-vine area this year), right now there is a greater mass of vegetation here. We went through and did a hand and hoe weed pass in a particularly bad block (the 13 rows of 777 have poor vigour) after harvest. We then applied a liquid compost fertigation to this block (all organic blocks in fact) to coincide with the autumn root flush.
The third aspect of the weed competition relates to the width of the former weed-strip. The inter-row sward prior to conversion was very narrow. The weed sprayer had been set to cover a very wide strip (prior to our acquisition of this vineyard three years ago), and in the organic blocks there is now cover between the former boundary of the inter-row sward and the discing gutter of the under-vine weeder (which is narrower than the former weed strip). A little hard to visualise perhaps, but it all equates to a significant area of soil around the vines that was formerly bare earth and is now covered in competing vegetation.
The plan moving forward is to look at applying regular microbial and nutrient boosters (instead of one-off biennial compost applications), in addition to some inter-row cultivation. The 13 rows of the 777 block serve as a good experiment area, and we plan on trialling a few different things down these rows, keeping a control so we can look at the comparisons. Bart has recommended some blood and bone, which we’ll look at putting on in two applications in early spring. We will also look at some liquid fish fertigation and increasing our vigilance with the vegetation cover and timing of weeding/mounding passes.Last but not least, some truly outstanding fruit was harvested off School House for vintage 2013. There was some botrytis in the Pinot Gris again – though markedly lower incidence and severity than last year – and the conventional blocks that were sprayed with Switch had virtually nil. The assessments from Fruition showed that we still have a decent (growing) leafroll caterpillar population, and we’ll look at a BT spray post flowering next season to control these populations (which could be affecting the severity of botrytis also). Grapegrowers and winemakers very happy, with excellent physiological ripeness through the vineyard and fruit coming in ripe with slightly lower sugar levels than usual (a good thing!).