Will this Silica spray help all bonsai to help with fungus?
I believe the silica will help more with the formation of the cellular structure and strengthening of the vascular tissue as it develops. This may inadvertently assist with disease and pest resistance as well as drought tolerance. I would use copper fungicide, neem oil, vinegar, or hydrogen peroxide sprays for fungal treatments. Alternatively, there are products like daconil & cleared 3336 and other systemics that can be used. I usually resort to the aforementioned suggestions for fungal control. Also, I do not water the foliage and do my best to prevent over-watering.