Bonsai trees are very delicate and are susceptible to decay, disease, damage, and infestations by pests. Lack of proper care is one of the top reasons for these problems, and if your tree gets into trouble you will need to know how to treat the tree without damaging it.
Some of the problems that you may come across include spider mites, scale insects, mealy bugs, aphids, green fly, black fly, and gall aphid. There are also several different types of moths that can attack a bonsai tree. They include the goat moth, leopard moth, geometer moth, and ermine moths.
You will want to watch the leaves of your plant, spider mites and greenhouse mites attack the bottom of the leaves that will leave marks, holes and discoloration as signs that they are present. You may also notice webs on the tree, as there are some types of pests that will leave webs as an indication of infestation. You will need to treat the tree at the first sign of infestation. Spray the foliage, especially the undersides, with insecticides, mild symptoms can be handled with acaricides. You will want to use a variety of acaricides to keep the pest from adapting to the chemical. Red mites and spider mites will also attack the needles of evergreen trees and will need to be treated immediately. With evergreen trees, check the cracks in the bark for eggs, this is the mites preferred location for laying eggs.
The needles of evergreen trees will turn a brownish color when they are infested. Caution is needed though, be aware that evergreen needles will turn this color naturally during its’ winter dormancy period. Look for the webs that the mites leave as an indicator also. If your bonsai is evergreen or deciduous you can wait until warm weather and do further treatment by removing, and destroying the affected branches, and foliage.
Another sign of infestation that you can check is the leaves for the eggs. Most pests will attach their eggs to the bottoms of the leaves, and these will show up as red spots on the leaf. The eggs can be destroyed with oil-based products, or if the eggs are found on very few leaves, you may just remove and destroy the affected leaves.