Latex is a key product for many tropical countries, of which 80% is produced by smallholders. Latex is produced by the rubber tree (Hevea brasiliensis). Given the 7-year immature unproductive period, establishing a rubber plantation requires considerable investment by smallholders, emphasizing the need for sustainable management. The difficulty of performing an agronomic diagnosis of a tree crop is to obtain an accurate picture of current and past cultivation practices, to be able to assess their impacts on the agro-ecosystem as well as on sustainability. Smallholders do not usually keep records of latex yield or of their technical practices, making it impossible to perform a diagnosis based on productivity. As latex harvesting involves tapping the bark, which leaves scars on the trunk, we hypothesised that these morphological traces would be good indicators of current and past practices and would thus enable a diagnosis based on the economic lifespan of plantation. To this end, we formalised a tapping panel diagnosis that involved reproducing the scars on tapping panel diagrams, and analysing them using two indicators: the amount of virgin bark consumed and the number of tapping years that remained. We validated this tapping panel diagnosis in a sample of 25 smallholder plantations in Cameroon, where we characterised eight tapping management systems reflecting different levels of tapping intensity. The assessment of the respective share of each tapping practice on virgin bark consumption revealed major effects of tapping frequency and of shaving thickness. We showed that the tapping panel diagnosis used as a decision support tool can increase remaining tapping years by 33% to 355%. To conclude, the tapping panel diagnosis formalised here for the first time will be a useful support for the participatory development of innovating tapping management schemes involving both technicians and smallholders.