Part 6 of a series by Eugene Howell
We’re continuing our discussion about the pests that can infest your bonsai trees. My previous post talked about aphids and is linked to at the bottom of this page. In it we learned how to recognize when your bonsai have them, and what to do about it.
In this post we will discuss how to identify mealy bugs, scale, spider mites and thrip, and how to get rid of them.
Mealy bugs are easy to identify but more difficult to eliminate than aphids. Like aphids, mealy bugs mainly stay on the undersides of leaves, along the stems, and on the branches and trunk. They can be identified by their protective coating which is usually white and looks like a tiny bit of cotton.
One strategy for eliminating them is to create an oily spray (the recipe is in the previous post) and use it on the insects. The second strategy is to use an insecticide labeled for mealy bugs. Spray the tree thoroughly, paying particular attention to the undersides of leaves and twigs and branches. Do this again in 7 to 10 days to ensure they are completely eliminated. This method can also be used to eliminate the insect commonly called scale.
When scales are on the branches, stems, and woody parts of a bonsai tree, it’s easy to overlook them and not recognize what they are. They may appear as nothing more than a small brown, oval bump on the side of a branch. However, when they are the underside of leaves, their shape and color make them easy to notice. A typical scale will be about 1- 2mm in size. If you are not sure that you’re looking at a scale, scrape it with your thumb nail. The insect will be easily removed from the branch or leaf.
Of these five pests, spider mites are usually the most tenacious. The casual gardener has difficulty identifying that this pest is present and more difficulty in deciding what it is. Once identified, they can be difficult to eradicate.
Spider mites are extremely small insects. They usually cannot be seen with the naked eye until the infestation becomes a swarm large enough to notice. What frequently gives them away is the extremely fine webs that appear between leaves or between stems. But by this point, however, there can be thousands of mites on the plant and getting rid of them requires persistence and the right insecticide.
There are methods for detecting spider mites before their numbers become overwhelming. A 15 to 20 power magnifier will allow you to see them moving across the leaves. Another method is to hold a white piece of paper under a branch and then shake the branch vigorously. If tiny specks of dust fall onto the paper, watch them. If you see the specks begin to move, you have spider mites.
An insecticide is the most effective treatment for mites. There are several good ones on the market, but you need to make sure the label specifically says that it will take care of spider mites. Mites will seldom be eliminated by one spraying. It’s recommended that the bonsai owner spray once a week for two weeks and then once every three weeks for the next two or three months.
Thrip are interesting little critters and they especially love Ficus trees but can be found on nearly any bonsai. To identify them, inspect your tree’s leaves. If you see leaves that are rolled into a cigar shape along the mid rib, you likely have thrip. Open the rolled leaf and look for the small black insects crawling about.
The best way to eliminate thrip is through the application of a systemic insecticide. The reason a systemic is needed is due to this bugs habit of rolling up a leaf around itself and thereby creating a tent that protects it from sprays. A systemic insecticide is taken up by the roots of the plant and distributed throughout the tree by the circulatory system. It takes longer than a spray to be effective, but it does an excellent job.
A second, less effective, method is to pluck the curled leaves from the tree and burn them. This will eliminate the mature thrip, but not the eggs that may still be remaining elsewhere on the bonsai. When those hatch and mature, they’ll roll up more leaves and you’ll face the task of plucking leaves all over gain. If this cycle continues long enough you may end up with a naked bonsai.
Remember to always stay alert and keep on eye out for bonsai tree bugs. Don’t let the dropping of dead leaves be your first indication that your bonsai are infested.