Division (91) Extent

The extent of the damage indicates the quantity (%) of the affected part of the tree due to the action of the causal agent or factor, e.g. the % of affected branches.

The extent of symptoms reflecting defoliation (e.g. leaf damage by defoliators) indicates the % of the leaf area which is lost due to the action of the agent/factor concerned. This means that the extent should take into account not only the % of affected leaves, but also the ‘intensity’ of the damage on leaf level: physiologically it makes a difference for a tree if 30 % of its leaves show only some small holes or if 30 % of its leaves are totally devoured.

The affected leaf area is expressed as a percentage of the actual foliage at the time of observation.