Resistograph or sometimes known as Resistance Drilling Device

On Jul 2013, two Tembusu trees were observed to be not doing well and to be clear, these tree are not in the Singapore Botanic Garden. The trees have low density of foliage, and the ground within the dripline was compacted, as evidenced by absence of groundcover. Target is the carpark and cars that were parked there, occasional park visitors.

Crown area and trunk of the two Tembusu trees.

On Sep 2013, vertical mulching was done to break up the hardpan surface and to pour in used coffee grinds (organic matter) and NPK 15-15-15 (fertiliser).

Making vertical holes.

Overall view of the vertical holes filled with organic matter and fertiliser.

On Oct 2013, the tree on the left was observed to be still low in leaf density but the tree on the right had put out more leaves.

On Jan 2014, the pruning was done by the arboriculture contractor to remove dead branches.

On the same day, I was inspecting the work of the arboriculture contractor and also found that there is a possible cavity below the union of the tree (the tree on the left).

The extent of decay below the union, if any, was needed to be determined in order to ascertain whether the tree is safe. The depression may just be a natural pocket formed by V-shaped point of union. Hence, a request was sent out for quotations from arborists with resistograph or Resistance Drilling Device. The scope of work was of course to have the resistograph work done, first level tree assessment before that, and reports for both. The works were to be carried out at ground level, and three arborists came up with fees of $1800, $1500 and $1100, respectively.

A "Resi" or Resistance Drilling Device that is used to detect cavities in wood, which is a sign of decay. The company that manufactures this particular device, IML, could not use Resistograph to describe its device in some jurisdictions as the term was trademarked by another company, Rinntech.

The resistograph work was done on Feb 2014 and should be done again in 2 years to see if there is spread of the decay, if any.