Investigation of synergistic effects of extracts from Erythrophleum suaveolens, Azadirachta indica, and Chromolaena odorata on the durability of Antiaris toxicaria

The service life of non-durable wood can be extended with inorganic preservatives, but several are harmful to the environment and non-target organisms. Recently, eco-friendly types from organic sources including plants have been used. The influence of bark extracts from Erythrophleum suaveolens and Azadirachta indica, and leaf extract from Chromolaena odorata, singly and in combinations (all at 1.5%) was investigated in field performance tests with non-durable Antiaris toxicaria wood. Treated and control stakes (500 × 50 × 25 mm) were exposed for 5 years. Data included extract retention, visual durability ratings, and mass and hardness losses. Retention was greatest for mixed E. suaveolens and C. odorata extract and least for single E. suaveolens extract. For durability parameters, non-treated stakes performed worse than treated ones. E. suaveolens bark-treated stakes were most durable; those treated with mixtures containing E. suaveolens also performed well, while stakes treated with other mixtures performed similarly to the controls, except for hardness. The mixed extracts exhibited various effects. For retention, synergism exists between E. suaveolens and C. odorata, there was antagonism between A. indica and C. odorata, while E. suaveolens extract reduced the retention of A. indica. Regarding durability, no synergism existed between effects of the mixed components. However, E. suaveolens bark extract enhanced A. indica, and C. odorata ingredients, while the effect of E. suaveolens extract was suppressed when it was mixed with the others. These extracts are potential alternatives for inorganic preservatives, especially E. suaveolens and its mixed extracts, as its effects enhanced the others.