Midsummer advisor’s report

By Bart Arnst, Viticultural Consultant

December field visit observations

The second set of four field days at the Organic Focus Vineyards were completed in what was a very busy lead into Xmas.

Once again we had strong participation in both Central Otago and Marlborough, with attendees in Hawkes Bay being down on previous field days.

The Wither Hills sites had soil pits dug to compare any differences between the organic and conventional treatments. Matt Oliver from Huia led the discussion, the root trimming from the undervine cultivation being the only visible change. These are soils that have been worked for the past 50 years in horticulture — the land was previously an orchard before conversion to vineyards — so there are compaction and low soil biology issues to be dealt with.

Wither Hills have adapted an old spray tank which sits at the rear of their weeder unit and applies a commercial biological product to the ground each time they undervine cultivate. The planting of inter-row crops will help increase biological diversity and also begin to address some of the soil compaction issues, however a ripper may be utilised post-harvest to break up any deep pans.

The regrowth in the inter-row of the conventional block (in this case 100% herbicided pre bud burst for frost protection) was of interest with mallow, Californian thistle and clover being the first species to emerge.

The organic vines appeared to be slightly behind in growth at that point in December. Marlborough experienced one of its coldest spring and early summer weather periods, with talk of 10 days to 14 days behind where one would normally expect to be.

It is apparent in cool springs that the organic vineyards can be slower “out of the blocks”; add to that certain rootstocks such as Riparia Gloire and 101-14 and the effect can be quite dramatic. A syndrome I’ve cheekily named ASDS (a Stephen Donald season), where early on things look a bit ugly but can turn out pretty good in the end.

Mission Estate’s Mere Road block shows no visible difference in treatments at this stage. Demonstrations were given with Villa Maria’s Duo Cut mower and Mission’s Ridgeback undervine cultivator. Unfortunately there had been little regrowth in the undervine strip to show the Duo Cut’s capabilities, but participants were able to see its mode of action.

To date Central Otago has been having the pick of all our viticultural areas’ summers. Subsequently the Gibbston Valley site on Bendigo Station looks a picture, with most canopies almost full and looking very healthy. A frost event has somewhat taken the shine off the perfect start, but damage was isolated to small pockets and affected both treatments.

At the field days, all regions had a question and answer session before walking the vineyards to compare the differences, if any, between the organic and conventional management techniques.

Pest and Disease

The adverse weather over much of the flowering in Marlborough has encouraged growers to apply one if not two flowering sprays for botrytis protection. There have been significant levels of post flowering “trash” left amongst the clusters, so the removal of this (mechanical blowers) is to be encouraged before bunch closure.

All regions will be keeping an eye on powdery mildew through to veraison, although at this stage very little has been reported. Sulphur with addition of a spreader/surfactant (soap or fish based) has proven adequate to date.

Downey mildew has been seen in Marlborough this season, though those in the South Island would like to think it’s solely a North Island problem. Downey is best prevented by determining the likelihood of an infection. Fortunately the increasingly accurate weather forecasting allows the grower to be pre-warned. 10-10-24 is the formula: 10mm of rainfall, 10 degrees over 24hours. Caine (Mission Estate) is having good success with a copper application pre-infection period; obviously with the maximum allowable usage of 3.0kg/ha per we must be careful with rates.

The petiole and leaf tests will have shown whether any specific nutrient adjustment is required via canopy sprays or fertigation in each vineyard.

Weed control in the undervine strip will now be based around a needs be basis; there is unlikely to be any serious competition to mature vines from this point on to harvest. However, understory height must be controlled, as weeds can increase humidity as well as corrupt the picking sample with seed heads etc.

The next field days are scheduled for late February/March, where we hope to be somewhere between verasion and harvest.