If Pseudomonas (a form of bacterial canker that this cultivar of Japanese maple is extremely prone to) then don't bother. The bacterium is systemic and the disease will eventually kill the tree. It is better to start over with new, disease-free stock. But be aware that certain cultivars of Japanese maple - 'Sango Kaku' and other red barked forms, 'Katsura' and 'Corallinum' in particular - are extremely prone to this pathogen, which is easily stimulated in activity by cold, extended wet weather or other stress.