First season reflections: undervine life and disease pressure in Central Otago

By Max Marriott

Assistant Vineyard Manager, Vinewise Viticulture

We were blessed with an Indian Summer for our autumn harvest, with idyllic weather for the duration. Early botrytis pressure from the rains in February/March had largely disappeared, though it was evident during harvest that the Pinot Gris suffered more than the Pinot Noir. Interestingly, the conventional block of Pinot Gris had a substantially higher incidence and severity of botrytis when compared to the organic block. We suspect there are two primary causes for this observation. Firstly, as a saprophyte, botrytis occupies the vine understory as its habitat when it’s not on the vines themselves. The undervine area of the conventional blocks has no other microflora or microfauna competition, in addition to the surface being flat and uniform. We suspect that when it rains, the spores are dispersed far more easily in the conventional blocks that have this type of surface, when compared to the uneven cultivated mound of the organic blocks. The organic blocks, free of herbicide, will also have a greater variety of microorganisms in the soil undervine, creating greater competition and potentially a reduced number of botrytis spores.

Pruning, winter 2012

Secondly, the undervine area in the organic blocks has a higher degree of weed competition, in part leading to growth suppression through reduced water uptake (in addition to the surface root cutting that goes on from the disking). It’s believed that this reduced water uptake could lead to poorer fruit set and correspondingly more open bunches, when compared to the bunch architecture of the conventional blocks. Unfortunately this isn’t something that the project measured, but could perhaps be an interesting exercise moving forward. The conventional Pinot Gris is also located at the outside edge of the north block on the vineyard. The pocket at the bottom edge of this northern block sees quite aggressive bird pressure (despite the nets), so the severity of crop loss could potentially be attributed in part to the bird damage.

At the annual project review meeting in Marlborough this August, it was interesting looking at our results compared to those from the other regions. Considering this was our first year, and costs included establishment for the organic blocks (raising irrigation, staking young vines and irrigation valves), the costs per hectare were only slightly different. When fruit volumes were taken into account, the tonnage per hectare and costs per tonne of fruit were even more comparable. The desirable cropping rate in Central Otago usually oscillates somewhere between 5-7t/ha. The fruit thinning costs for the organic blocks were higher because there was more fruit to drop as a result of the smaller canopy. We expect the canopies to bounce back over the next two years, so it will be interesting to monitor this both with respect to physical size and colour (as mentioned in our last blog, the organic canopies showed a lighter green, sometimes yellow tinge).

Moving forward, there are some small changes that we’ll make and adapt to for the season ahead. We will finish applying the rest of our compost to the vineyard (we covered about ¾ of it last year) in September, and we have also graded the main headland area where cars park/travel. The intention was to make this area easier to travel through for staff vehicles, but also to sow some grass and monitor its growth relative to the organic and conventional blocks to see what changes occur (with particular reference to the surface flooding and washout that occurred during the past growing season on the conventional rows). We will again sow our two flowering cover crops – Phacelia and buckwheat – hoping to gain a better strike from our buckwheat this year and mitigate some of the damage from leafroller caterpillar that may have influenced the severity of our botrytis last year. We were very happy with our powdery levels last season – or lack thereof – and will continue with our 10-14 day sulphur and seaweed spray regime.

Pruning to prepare the vineyard for the project’s second season