Let harvest begin: comparing organic & conventional growth

By Jacqueline Maclaurin

Viticultural Technician, Wither Hills

What a season it has been here in Marlborough. Like the rest of the country it feels suitably like autumn. We’re looking forward to starting harvest and it’s a great time of the year to see how the past year has come together.

In this first year of the project it is interesting to note the differences we have seen in the blocks and the management decisions behind some of the management decisions. As I discussed at the field day we held in February, some of the differences I have noted so far between the organic and conventional blocks are the difference in phenological stages and canopy growth.

In the Pinot Noir, the organically managed block has been behind the conventional block from bud burst through to veraison (see photos at bottom). I believe that the undervine weeding may have had an impact on the growth rate – having done four passes with the scallop edged mounding disc cutting the surface feeder roots. This is something to be aware of, and as other organic growers have said, the vines may show stress in the first couple of years of organic management, until their roots become more deeply established.

In the Sauvignon Blanc, the canopy growth in the organic block was less than in the conventional, but the fruit maturity was on a par. Berry samples taken in late February showed no noticeable difference between conventional and organic in the Sauvignon Blanc. But there was a three brix difference in the Pinot Noir, with the organic being further behind.

Conventional Sauvignon Blanc

Organic Sauvignon Blanc

In terms of irrigation, the organic Pinot had more irrigation in February, due to the vines appearing water-stressed. This again could be due to the effect of the undervine weeding affecting surface roots, although there could be several other factors – rootstock and crop levels. Through the project, as our knowledge and understanding of organics increases, it may push us to think about these factors when making management decisions, such as an early bunch thin to reduce vine stress.

In terms of leaf plucking, the conventional Pinot Noir has had two machine passes (Collard and Gregoire) and one hand pluck. The organic Pinot Noir has only had a light Collard pass, due to the light canopy growth which has also followed onto no canopy trimming needing to be done this season. In the Sauvignon Blanc, leaf plucking was the same with both organic and conventional undergoing one Collard and two Hills passes. In terms of trimming, the organic block has only one trim and the conventional Sauvignon Blanc three so far this season.

Under organic management we have chosen to use an undervine weeder. Because of the season we’ve had this year, with a high rainfall in December, we have done more passes than we would have hoped. But this was a necessity to control the weeds undervine and make certain vineyard tasks such as bud rubbing an easier task, and reduce any further competition with the vines.

The Sauvignon Blanc has had three weeding passes with the scallop edged mounding disc, and in the past week a pass has been made with the blades to cut down the mound and dislodge any further weeds. When we did the first pass with the disc, each row was driven twice, to break up the soil that has been compacted on the edge of the wheel tracks over the past 11-12 years.

Our organic management advisor Bart Arnst has often mentioned the changing weed species undervine as the years under organic management increase, and although the Sauvignon Blanc has only been undervine weeded for nine months, we can already see the change from the mallow weed species to fat hen.

The canopy spray programme that we undertook this season is a reflection of Wither Hills’ stringent management strategy. We have chosen to use sprays which may be slightly more expensive, but are known to be effective.

For example we have chosen to use Serenade Max for botrytis control over the flowering period and pre-bunch closure in our organic blocks, and Switch at flowering and pre-bunch closure in the conventional blocks. As we have done our own company pest and disease monitoring during the season, we have also sprayed in response to disease threshold levels reached. We have set the thresholds and so have kept a tight spray programme for powdery mildew cover in response to this – a cover spray, typically Kumulus and Protector every 10-14 days, or extending this out when the weather allows. With downy mildew showing up in Marlborough in January, we put on further cover sprays such as copper or potassium bicarbonate.

Hopefully there will be no further need for canopy sprays now, with the nets on and bird scaring well underway. Now we are starting to plan for what winter cover crops or permanent sward we may sow in the inter-row, and for making compost post-harvest.

Conventional Pinot Noir, March 14

Organic Pinot Noir, March 14

Organic Sauvignon Blanc

Conventional Sauvignon Blanc