Bonsai Pests

Part 5 of a series by Eugene Howell

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Pinus BonsaiYou’ve got a beautiful bonsai that’s planted in the perfect bonsai soil, watered daily, fertilized well during the proper part of the year, pinched when needed, and repotted every few years. You’re rewarded with a tree that grows vigorously, blooms profusely and is the picture of perfect health. Then one day you notice the leaves beginning to do strange things. Some have a mottled appearance, with tiny yellow spots all over them and others are beginning to curl up like a rolled cigar. If this hasn’t happened to you before, it can leave you puzzled as to what’s going on.

Bonsai trees can often be a paradise for bugs. The sooner we learn to recognize the symptoms and identify the insects, the better chance we’ll have of saving our trees and returning them to health.

Let’s first talk about the more common pests that attack bonsai trees. There are five to watch out for: aphids, mealy bugs, thrip, spider mites and scale.

All five of these pests do the same thing; they bite into the leaves or stems of the tree and suck out the sugary sap. Initially this can cause yellow spots to appear on the leaves. If hundreds of these insects are invading your bonsai, all the leaves will become mottled in coloration and will eventually die if the insects are not eliminated. This can also happen to whole branches and in very severe infestations, can kill the bonsai.

Aphids are tiny, pear-shaped bugs that are easily visible with the naked eye. They can be light green, brown, or black in color. There are two simple methods for determining if your tree has them. The first is to examine the tops of the leaves. If there is a black, sooty-looking substance covering part or all of the leaf, then you have either aphids or mealy bugs. This substance is called sooty mold and is a sure giveaway for these insects. The second way is to turn leaves over and examine their undersides to see if you can spot the insects themselves.

One way to remove them is to spray the tree with a strong stream of water. You need to pay particular attention to the undersides of the leaves and stems. One spraying will not eliminate them completely. Some will hang on and some may return, but the total number will have been significantly reduced. If you do this a few times you should be able to rid the tree of them.

Aphids can also be easily eliminated using either a home-made spray or an insecticide labeled for aphids. The home-made spray is mixed as follows: into a gallon of water put 3 tablespoons of cooking oil and 3 tablespoons of baby shampoo. Mix gently to prevent suds and then spray the undersides of leaves, stems and on the trunk. Repeat in 10 days. (Oils should never be sprayed on Buttonwoods or Fukien tea).

By learning to identify aphids and other bonsai pests, you’ll be able to keep your bonsai trees alive and healthy for decades.

Tomorrow we’ll talk about dealing with mealy bugs, scale, spider mites and thrip.

Part 4 of this series : Part 6 of this series

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