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Performance of naturally durable eucalypt posts in Marlborough vineyards

By Paul Millen and Clemens Altaner, October 2017.

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Executive summary

The area of vineyards in New Zealand is up from that reported in 2015, which was 35,463 ha. Posts in a vineyard average 500-600 per hectare so there are approximately 17.5 to 21 millionposts in New Zealand’s vineyards. The predominant reason for post breaking is mechanical harvesting and mechanized pruning operations with an estimated 5% of posts failing annually. Therefore, the New Zealand wine industry is estimated to require about 1 million replacement posts annually.

NZ vineyards are dominated by Copper Chromium Arsenate (CCA) treated radiata pine posts. There is opposition to the use of CCA treated wood because of the heavy metals used as preservative. Broken posts can be recycled but ultimately they become hazardous waste requiring a secure landfill or a highly controlled incineration facility for safe disposal.

As a result organic agricultural production standards, both in NZ and overseas, have banned the use of CCA posts for replacements or in new development of certified organic vineyards.

This project aims to demonstrate to forest growers and vineyard owners/managers the potential for naturally durable eucalypt timber to be used as vineyard posts, and to highlight market opportunities to give growers confidence to invest in planting durable eucalypts.

Vineyard Timbers sales records show a total of 746 E. bosistoana and 298 E. globoidea posts being purchased by six Marlborough vineyard owners from 2006-2009. All posts were installed in vineyard properties within the lower Wairau Valley which is the central locality of vineyards in this region. The posts were installed as replacements for broken CCA posts by four vineyard owners while one owner used them in setting up a new vineyard and another has them in use in a small feijoa orchard. The vineyard owners and their eucalypt posts are the focus of this project.

The six vineyard owners were contacted to answer questions on their knowledge and experience with using these posts and to request access to their vineyard to locate and assess the posts that were still in service.

Five of the vineyard owners manage their properties under organic standards with mechanical harvesting and some mechanical pruning and two with under vine mechanical cultivation.

Five vineyard owners/managers answered the questions about the posts with their feedback generally positive due to the posts being naturally durable and acceptable for their organic standards. Three reported a few posts broke during harvesting. This was attributed to large knots in the posts. No report of failure due to decay was received. The main negative comments were that the timber is too hard for easy nailing or fastening wire hangers – predrilling was deemed necessary taking too much time. Furthermore, the lack of regular supply was raised and one owner had problems with timber twisting in storage due to cross grain.

Four vineyard owners/managers would use the posts again if they were available with two suggesting the posts could be larger. Four also commented that certification of sustainable production or local production was important as was price.

Visits were made to all vineyards to locate and test over 1,000 functional eucalypt posts still in service. During site visits to vineyards 1065 posts were found still in service; another 14 were found broken; 1 failed from decay and 45 were in storage. This was followed by selecting a sample of 150 posts in service across 4 vineyards to assess the post condition in the top 200 mm of the soil horizon where maximum decay is likely to occur.

Generally, E. bosistoana posts showed less decay than E. globoidea posts after 8-10 years in service. However, this analysis was confounded by site, as not all sites had posts from both species.

E. bosistoana posts performed very well at both assessed sites with many posts showing no sign of decay. Performance of E. globoidea was site specific. After 10 years in service posts, E. globoidea posts at vineyard 2 had severe decay while posts in a small feijoa orchard at vineyard 3 show little decay.

The posts assessed in this project were not installed in a dedicated scientific test to assess durability but part of commercial vineyard operations. The feedback from vineyard owners/managers and the results of our decay assessments demonstrate that most of the durable eucalypt vineyard posts of both E. bosistoana and E. globoidea are continuing in service after more than 10 years with a very low percentage of broken posts found in the post assessment; in the case of vineyard 1 this was equivalent to annual breakage of only 0.3%.

It can be expected that most of the posts will continue in service and that another inspection could be made in five years.


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