I'm desperate to save the life of my 9 year old carmona bonsai which I think I may have damaged by using insecticide. I've had the tree for about 5 months and until recently it looked really healthy so I presume I was looking after it correctly. However it became infested with greenfly and whitefly with which I was fighting a losing battle by trying to remove them by hand. About a month ago I used a houseplant insecticide just once, but since then my bonsai has been producing yellow leaves which eventually drop off. This has been at the rate of about 5-8 daily. I keep the plant in my kitchen in a roughly north facing windowsill where it gets some early morning sunshine. I water every 2-3 days by immersing in water up to top of soil for 10 mins and then draining. I've fed it occasionally with weak houseplant food. I've tried washing the leaves under the tap to remove any residual insecticide to no avail. Oh, and the pests are back in force! Is there anything I can do?
I didn't find the right solution from the Internet.