Bonsai Growing Guides
Battling Pests on Bonsai |
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Since the spring of 1996, we have been growing our entire collection of prebonsai and bonsai organically. We like to grow all our plants in the most earth friendly way possible and bonsai at first seemed a bit scary to take this jump in cultural practices. Our paranoid side said "some of these trees are old and expensive, we don't want to kill them trying something crazy.
Fortunately, we ran across several books written in Japan in 1920's, 1930's and 1950's, which were translated into English in the 1950's and 1960's. Since these books were originally written before the widespread development and use of synthetic, chemical pesticides after World War II, 90% of the pest control information in them was organic. What a Find! We have learned many things about bugs from the old masters that wrote these books and are learning more each day.
We have noticed over the past 5 years of organic bonsai growing that insects love stressed trees. The most important thing a bonsai grower can do is keep their trees happy and healthy by proper and timely watering, fertilizing, root pruning and repotting; as well as proper light and temperature conditions for the particular species.
Water stress, fertilizer stress, light stress, temperature stress, and being too potbound are the most common root causes for insect infestations in bonsai. The more closely you can duplicate the native climate and environment of a tree, the healthier and less stressed it will be. So, the first and most important way to avoid insect problems in bonsai (or any other plant for that matter) is to know the tree, duplicate the trees native conditions as closely as possible, and don''t accidentally stress the tree.
If two trees of the same species are growing next to each other, the stressed tree will invariably get infested with insects before the healthy tree. We have seen this phenomenon so often that as soon as we see insects on a tree we try to determine if the tree has been too wet or dry, too potbound, too hungry (or overfed) or in a less than ideal location. We will try and remedy the root cause of the infestation as well as the actual pest problem itself. Once the root cause of the insect infestation has been remedied, recurring infestations will generally cease.
Let the bugs help you to figure out what is not right with the tree. Another observation we have made is that certain species of bonsai are more attractive to certain species of pests. In our greenhouse we scout the plants daily looking for certain pest species on certain tree species. Scouting for insects in this way has allowed us to catch most insect infestations early and keep them to a minimum. Determining the root cause of the infestations will help keep them from recurring. Call it "wholistic" bonsai growing.
During central Maine's cold and snowy winter season, our temperate and cold weather bonsai are sleeping happily in their winter homes. We store our temperate trees in an unheated basement (minimum temperature 29-25F), a cool greenhouse (28-40F night temperature, 40-70F day temperature) and an unheated hoophouse (22-40F), depending on the species, age and condition of each tree. See temperate care guidelines.
We have found that this is the best way to keep them stress free and happy. An unstressed and healthy tree is the best prevention to insect infestations. All temperate trees need their dormant period. The lives of the cold weather trees actually depend on it. If any insect eggs happen to be found on the dormant trees they are easily treated organically with dormant or horticultural spray oil before any new, green growth is visible. We personally have had to do this only once in the past five years but many growers find spray oils to be a good organic preventative measure.
Also during this cold and snowy winter season here in central Maine, our subtropical and tropical trees are confined to our warm greenhouse. Insect problems can be more severe during the winter months on tropicals since they are not accustomed to the short days of high northern latitudes, they receive much less air exchange and there is a more limited population of beneficial insects present than when the plants are outdoors during the warm part of the year. See tropical care guidelines.
We run our greenhouse at 55-64F night temperature (depending on how close to the heat source you are) and 80F maximum day temperature and have found certain trees prefer certain temperatures. The cool night temperatures slow down the speed of the insect pests life cycle, making population explosions slower to occur and easier to find and control.
Mid-winter through mid-spring is also the time we do much of our training, pruning, repotting, root pruning and rock dust applications, which remedies several of the root causes behind many insect infestations.
Read This Paragraph Carefully. According the United States Environmental Protection Agency (EPA), any violation of instructions on the pesticide container label (this includes organic materials as well) is a violation of Federal Law and makes you subject to arrest, imprisonment and/or fines. We don't say this to raise the already too high ambient paranoia level in this world, but: Read the Label before you apply any pesticide to anything, organic pest controls included. On the label you will find all the information you need to make a successful pesticide application: the pest(s) controlled, the mixing instructions, any special application procedures, cleanup and disposal procedures, everything.
Since pesticide labels can change on an annual basis, we will be making only general control recommendations here, since any incorrect use of a pesticide can open up the potential for arrest, imprisonment or fines issues mentioned above. The most current pest control information is not only the most accurate; it is also the most legal in the eyes of the EPA. So, Read the Label each time before you purchase and/or use any pesticide for any reason. It will also help to make the world a less toxic place.
Several species commonly grown as bonsai are very sensitive to many pesticides; most notably Chinese elms and Fukien teas. The most common symptom of this sensitivity are phytotoxic reactions such as leaf burn or leaf drop. They usually don't kill the tree but phytotoxicity will increase the stress level in an already stressed tree. For sensitive species, we have found that rinsing the plant thoroughly with clean water within 24 hours of an application of an insecticidal soap or horticultural oil spray will reduce the risk of a phytotoxic reaction to almost nothing. High air temperatures (above 75F) can also promote or enhance phytotoxic effects.
We try to schedule our spraying for cloudy days when temperatures are cooler. However, sometimes the spray schedule does not allow us to wait until the sun and temperature levels are just right. On those occassions we schedule our spraying for the morning or the evening hours.
Insecticidal soaps generally are most effective on soft-bodied insects, which are species without protective coverings or a hard exoskeleton. They dissolve and soften the soft exoskeleton of the insect, causing death. Insecticidal soaps are only effective against living insect pests, not their eggs. Several sprays 3 to 10 days apart (depending on the insect species to be controlled) are necessary to kill the young hatchlings as they hatch after the initial spray. Read the Label to learn what, if any, follow-up sprays should be made, it is on there.
Horticultural and dormant oil sprays are formulated from highly refined petroleum oils. The horticultural oils are generally more highly refined and may therefore be used on many species while they are in leaf. Dormant oils should be used on temperate and cold weather trees only during dormancy, since they can cause phytotoxic damage to the tree if applied when in full leaf. These products are effective on most insect species and their eggs. They act by coating the insect body or egg case with a thin film of oil, suffocating the pest or soon to be pest.
Hot pepper oil is effective on most insects, excluding mature scale insects. This material also acts by softening and dissolving the exoskeleton of the pest, but is a stronger compound than soap and will kill insects with hard exoskeletons. As this oil is made from hot peppers, it is hot to humans also and will cause skin irritation, eye watering and burning and all the other things hot pepper sprays do to muggers and criminals when they get sprayed. So be careful and Read the Label.
Neem oil is derived from the oil of neem seeds, a tropical tree native to India. It is most effective as a repellent and is best used after initial control of the insect is reached by other means to discourage a second infestation. Garlic spray formulations also are best used as repellents. For specific insects repelled by these sprays, Read the Label!
Fungus gnats are a common but misunderstood insect often found flying around indoor tropical bonsai during winter. This insect actually does little, if any, direct damage to the plant. They are dark colored and are similar in size and shape to the fruit fly. The larvae live in consistently damp or wet soils and feed on decaying bits of organic matter. The adults only live for several days and don''t eat anything as they fly around and mate. Their eggs are laid in the soil and the life cycle repeats itself.
Fungus gnats are not harmful to the tree directly, but they are indicative of a treeto water or not to water... that is not being allowed to dry out sufficiently between waterings and as a result serve as a warning to revise your watering before the plant becomes stressed. You can easily revise your watering schedule by allowing the soil to sufficiently dry between waterings. The larvae will then die, the adults will fade away in several days and this insect problem will be solved without any spraying at all.
The most common insect pests afflicting bonsai in northern climates are: aphids, spider mites, scale insects, mealy bugs and whitefly. These pest can afflict a wide range of plant species, there are also many other pest which are species or genus specific. For pest pictures and control suggestions for these and other pests check Insects on the Web and Ecological Garden Projects and remember to Read the Labels on the pesticide containers at your local nursery or plant store before purchasing the control agent.
There are several other things we do in our "wholistic" control program. We try to spray only the insect pests we wish to eliminate and only on trees that are actually affected. We work around the spider and ladybug populations in our greenhouse, moving a wandering spider or ladybug from a plant to be sprayed. Both of these beneficial insects can eat many pest insects per day if they are alive to do so. For light infestations, handpicking or crushing the little buggers works well.
Unless using horticultural oils at the appropriate time of year, (as stated on the label) adult scale insects need to be crushed or scraped off the tree with existing organic methods currently available. Young hatchlings can be controlled with materials designed for use on soft-bodied insects. Light aphid or mite infestations can often be controlled with a jet of water from a hose or sprayer.
Check our watering and fertilizing guidelines in the bonsai section of our website for more information on watering and fertilizing. Failing to repot your bonsai before it becomes excessively potbound will result in a tree getting insufficient water for healthy growth and more stress from a hard root pruning when the tree is finally repotted.
Fertilize your trees only when they are actively growing. Water appropriately for the season of the year and the plant''s needs, not by the calendar since plants can''t read. They don''t know (or care) what day of the week it is. Trees respond to excessive drying out with wilting, leaf drop, decreased pest resistance and death. They will also respond to excessive soil moisture with decreased insect resistance, slow growth, root rot and death. Fortunately they will also respond to correct watering and fertilization practices with healthy and happy growth and increased pest resistance.
Good luck in all your botanical endeavors and until next time, Happy Gardening.
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