Bonsai Pests: Scale - no small scale problem

Scale are insects that most often resemble a small oval scale on your bonsai tree. If one does not look closely they may mistake it for a part of the bark. These insects should not be taken lightly as they feed off your bonsai trees' fluids like vampires and can cause leaf drop, branch die back, and eventually, in severe cases, death of the tree. They are of special concern if one keeps their bonsai indoors due to lack of natural predators to keep the infestation in check.

What scale looks like

Scale is oval in shape and is usually a brown color. They can also vary as being more yellow or green as well depending on the species. In adult form they can measure between 3 and 4 millimeters long and are roughly 2 millimeters wide. In nymph form they may appear whiteish or yellowish. As the nymph matures they tend to take on more of a yellow to brown color. As noted previously, they may look like scales or raised bumps flush with the bonsai tree. Be sure to check the undersides of your tree's leaves and the growing tips as they tend to congregate in those locations. Scale secret an armor over their body consisting of a waxy secretion. This armor make them resistant to many insect treatments.

Scale life cycle

It is important to know the scale life cycle so one can know how best to eradicate them. This is because treatment is only effective at certain times of the scale's life cycle. Female scale insects give birth to their eggs while they are still inside her. These newborns are called crawlers and it is at this stage that most insecticidal treatment methods are most effective. Once these crawlers settle down and begin feeding they never move for the duration of their lifetime. They stay in the same spot and mature over the process of 60 or so days. Over their lifetime they shed off layers which form a protective coating over them which make them highly resistant to insecticides. Most treatments attempt to kill the scale while they are still at the crawler stage before they can mature and develop this coating.

Getting rid of scale: Scale treatment

There are several approaches to getting rid of scale, but they all involve physical removal and sprays. It is best to combine both methods to get rid of them as quickly as possible to lessen the damage to your bonsai tree. As mentioned earlier, once the scale matures it will be resistant to sprays so spraying alone over time should kill all the young which should eventually cause the scale infestation to die off. The keyword here is eventually. For faster eradication of the scale one should also physically remove any visible scale from the tree. Scale can usually be scraped off the tree using a fingernail or something with an edge to it. Additionally, some people prefer using tweezers or a tooth pick. Dabbing scale with a q-tip dipped in isopropyl alcohol will help to loosen the scale. This method should be combined with spraying an insecticidal solution on the bonsai tree to kill any young. This may need to be repeated for 2-3 weeks to eliminate them completely.

Scale sprays and insecticides

Spraying the immature scale with insecticidal solutions will kill the young and cause the population to die off. Sprays most commonly used are of the home made variety or a commercial insecticidal soap or oil treatment such as neem oil. The home made insecticide we found that works quite well is listed on our miticide recipe page and works equally well on scale. If you go with something store bought try to find something with neem oil in it and the label says is safe for your tree.