In Zen Buddhism where the practice originated, the art form of bonsai creation wove themes of man, nature, elements and change into a form of meditation and expression. While bonsai is not necessarily considered with such reflection in today, it is still a horticultural wonder that links us closer to harmony, nature and imparts beauty to our homes and gardens. While a bonsai's care isn't particularly difficult, it does require careful watering and preventative care, especially in regard to pests.
There are four categories of insects that primarily plague the bonsai--spider mites, whiteflies, mealybugs and aphids. Spider mites are tiny spiders that suck the chlorophyll from the leaves and remove the outer coating. Tell-tale signs of spider mites include yellowing of leaves or tiny spots. Whiteflies are tiny white flies that under magnification look like moths but from a distance resemble dandruff. Like the spider mite, whiteflies cause yellowing of leaves and can prevent the bonsai from thriving. Mealybugs are powdery-white, soft-bodied, oval-shaped bugs with grayish threads of wax. Like whiteflies they can weaken the bonsai and prevent the tree from thriving. Aphids, like the spider mite, suck the life from the bonsai. Green, tan or yellow in color, they have small legs that stick out from the body. Unchecked, aphids will kill the bonsai.
Pyrethrum, a highly toxic poison to garden pests, is derived from the painted ladies or painted daisies. Though commonly sold in gardening centers, Mother Earth News recommends if you want to maintain an organic approach, you should make your own pyrethrum dust. Many commercial varieties are laced with toxic, inorganic poisons. While it can be sprinkled around the perimeter of your bonsai pot as a preemptive pest-control measure, you can use it locally on individual plants for infestations. If you pick, dry and crush the flower petals, it can be sprinkled as dust. It can also be mixed in hot water into a tea, cooled and and sprayed directly on the insects. While you should use caution with any insecticide--organic and inorganic--pyrethrum is toxic to soft-bodied insects and nontoxic to humans and pets.
Neem oil, derived from the Neem Tree Nut (Azadica Indicais) a fungicide, insecticide and a miticide. Because it's nontoxic to humans, mammals or beneficial bugs, it has been used in Southeast Asia for generations as a mosquito and lice repellent, and by farmers as an insecticide and miticide against aphids and whiteflies. It is also effective against spider mites, a variety of plant diseases and caterpillars. It can be applied through spray or painted directly on the leaves.
Dietary diatomaceous earth is a nontoxic preemptive physical barrier that prevents insects from infecting the bonsai. It's sold as a dietary supplement. Also known as fossil shell flour, it is composed of ground diatoms--microscopic fossils mined from water deposits. Diatoms are single-celled plants and plankton that live in the sea and serve as a food source for all marine life. Diatomaceous earth works by scraping the exoskeleton of the insects and render them vulnerable to disease, elements and predators. It can be spread in a fine layer over the bonsai soil.
Predator Mites and Lacewing Larvae
An increasingly popular weapon against mites is the use of predator mites. While used predominantly in nurseries as a population control measure among destructive mite species, predator mites are most effective if systemic insecticide spray isn't used. While choosing this method for one bonsai isn't the best option because of the high cost of predator mites, if you have a persistent mite problem in your garden and among other household plants, it's worth a shot. You must choose the right predator mite for your situation. Some are more adaptive to particular climates, humidity levels and temperature ranges. Predators mites are available through mail order from varies online bio-control companies.
If you have persistent problem with aphids, one method other than sticky cards is to purchase lacewing larvae. Green Lacewing larvae are gray/brown in color, have a voracious appetite and suck the fluids from the bodies of their prey. While they are effective at controlling aphid populations, they will also eat spider mites, whiteflies and a variety of other pests that plague bonsai.
The best approach in preventing insect infestation in bonsai is prevention. If you examine your bonsai daily for insects, it's easier to pluck them, spray with an organic essential-oil based insecticide or repellent like soap spray and monitor. While the bonsai is technically a tree, albeit artistically pruned into a minimalist form, if healthy and strong, it should survive an occasional bug. But, a couple bugs can easily turn into an outbreak of pests that can further predispose your bonsai to disease. Since bonsai's are unable to outgrow infestations, they can die off rapidly.
Another preventative measure is to spray the bonsai with an organic soap-based insecticide. Soap acts as an adhesion that holds the oils to the leaves and stems. Many on the market incorporate essential oils and herbs like garlic, clove and citrus oils with a liquid soap or glycerin base. While one application should protect your bonsai, it's wise to spray insecticide every four to six days for up to a month to completely get rid of and prevent future infestations. Before using the insecticide on the entire plant, sample on one leaf to make sure it's not toxic.