Rotten wooden support posts have become quite an issue, replacement posts have been found to rot in as little as three years.
Post rot would seem to be quite a problem for anyone who uses wooden posts to support vineyard trellises. This problem is no doubt due to the EU ban on the principle chemical mixture that was used for many years to tanalise wooden posts. The chemical mixture used pre 2004 was called “Copper Chrome Arsenic” (CCA) this was banned for use in the UK in 2004. Replacement treatment chemicals have been tried, but unfortunately these do not seem to offer the long term protection of the CCA.
The posts typically rot within 150mm of where they go into the soil. Anything above this depth (or below) seems to survive very well. Many of the the posts in the original area of the vineyard are now rotting through at ground level.