NEW DEVELOPMENTS IN CHEMICAL CONTROL OF WHITE ROOT DISEASE OF HEVEA-BRASILIENSIS IN AFRICA

The main three parasites on Hevea brasiliensis roots in Africa are Rigidoporus lignosus, Phellinus noxius and Armillaria sp. Only R lignosus, which causes white root disease, exists in all the Hevea-growing zones and remains the main cause of death throughout African countries. New fungicides have been tested to improve the control of white root disease caused by R. lignosus. Some of the triazole compounds have proved very effective in vitro and in small-scale experiments on seedlings or stumps placed in artificially infected soil. Two applications spaced 6 months apart in liquid form (Alto, Sandoz) or triadimenol applications in granular form (Bayfidan, Bayer) at 0.5 g a.i. per tree, have given good results in field trials. Their use is recommended in practice.