Common Pests & Diseases of Bonsai

TreeBay

This is a work in progress intended to cover some common bonsai pests, symptoms and means of control. _This material is being compiled into the bonsaiTALK pest and disease Faq.

ANTS
Ants are quite common and favor bonsai soil because it is usually well drained and accessible. _They may choose to set up a nest or series of nests that will colonize your entire bonsai collection in short order. _While their underground activity is rarely harmful to the tree, they often harbor other insects, like aphids, mealybugs and scale, which may have very negative effects on your trees.

Identification of ants is easy. _Control is more difficult. _Ant stakes and insecticidal sprays may be helpful. _Identifying the source of the ants is paramount. _Drenching the entire bonsai plant by immersing for several hours in water with a drop of detergent may help flush out the colony.
[*] http://ohioline.osu.edu/hyg-fact/2000/2064.html

APHIDS
Tiny soft-bodied insects whose color ranges from light green through black. _Sometimes winged. _Size ranges from 1/6 inch to nearly invisible. _These insects group in clusters on the stems and leaves of bonsai, favoring succulent new growth.
They feed by sucking the sap of trees and shrubs. _Affected leaves may yellow or curl _Common controls include pyrethrin spray, insecticidal soap, malathion, oil-based dormant spray on deciduous plants in winter. Natural predators include Ladybugs and Lacewings.

BEETLES
Larvae and adults of beetles may feed on the roots and foliage of bonsai. _One particularly troublesome pest is the Japanese Beetle introduced in 1916. _Adults eat the soft material between leaf veins, which they leave untouched. _Grubs are active in the soil. _Control may be achieved through natural predators or insecticidal spray.[*] http://ohioline.osu.edu/hyg-fact/2000/2504.html


BORERS
A variety of insects have larval stages that infect the bark of bonsai, feeding mainly on the cambium and softwood areas between the bark and wood. _Their activity may impede the flow of sap and result in the death of branches or trunk. _Sudden, otherwise unexplained death of branches is quite often the cause of borers. _Look for tiny 1/8-1/4" holes in the bark of trees, sometimes accompanied by sawdust that identifies the entry or exit points. Controls include Lindane

FIREBLIGHT

LEAFMINERS

MITES
Mites are scarcely visible, but their damage to growing buds and shoots can be devastating to a bonsai. _ _Their activity may cause yellowing and death of the leaf or bud. _Look for dry or curling leaves and the presence of tiny webbing. _ Flicking an affected branch over a sheet of clean, white paper may result in the appearance of tiny black flecks that create red smears when rubbed with a fingertip. _

Mites may affect many bonsai varieties, including fruiting and evergreen species like juniper or pine. _They are often a problem on indoor trees where natural control by predators is not possible. _Mites may be controlled with insecticidal spray or malathion when they are active. Volck oil in the dormant period may also be effective.

Root rot (fungus)
Not all soil-borne fungi are bad. _However, a variety of fungal types can result in the rot of roots in a bonsai throughout its life, from the period immediately following germination (sometimes called "damping off) through the mature plant. _The fungus Heterobasidion annosum is one of the most prevalent fungi. _Root rot can lead to the loss of an entire bonsai within a few weeks. _Improper watering and overwatering of plants is often the cause. _Stressed plants can be more susceptible, and periods of extended rainfall can create ideal conditions for the fungus.

In conifers, it may account for needle loss and browning of new growing tips. _The newer growth is affected first, which helps to distinguish root rot from the normal process of seasonal needle replacement. _Yellow foliage and limb dieback are common, and are easy to confuse with other causes. _Azaleas are prone to root rot.

Control is difficult from the standpoint that the chemicals used in Fungicide drenches are toxic and much of the damage has already been done by the time symptoms appear.

Preventative measures include insuring that soil incorporates perfect drainage by screening soil and repotting regularly. _Proper watering practice is also mandatory. Composted _bark has been shown to be effective in reducing losses in some species.[*] http://www.aces.edu/department/ipm/Woody.htm[*] http://helios.bto.ed.ac.uk/bto/microbes/heterob.htm[*] http://www.bugwood.caes.uga.edu/factsheets/98-031.html[*] http://www.mykopat.slu.se/en/root.html

[b:8cdacd4487]MILDEW[/b:8cdacd4487]
Powdery mildew appears as a white bloom on leaf surfaces, typically the underside of leaves, affecting primarily broadleaf plants that are allowed to remain damp into the evening. _Affecting the growth of new leaves, powdery mildew may cause them to curl and twist into deformed shapes.

Controls include fungicidal soap. _Be careful not to wet the leaves of your bonsai in the evening as this promotes the growth and spread of mildew. _ _Move plants from shade into sunshine to reduce the conditions that mildew favors.

NEMATODES

Sometimes called "eel worms" these tiny pests form galls in the roots of bonsai, causing stunting and strange growth.

SCALE
Scale insects suck sap from the branches of trees, favoring fruiting plants, but also seen on others like oak and elm. _Difficult to see because of their natural camouflage, they tend to appear at branch unions, sometimes in conjunction with ants. _Affected branches will lose strength. _Rubbing the branch with a fingertip will cause the scale to slide off and expose the soft underbody of the insect. _ Look for bumps and warty protuberances along otherwise smooth bark.

Affected areas should be cleaned by hand and then Insecticidal spray or volck oil may be applied.

SPITBUGS
If you find your bonsai has been overtaken by a ball of clear, foaming mucus, you may have identified a spitbug. _Flushing it out of the foliage of your tree with a jet of water is an affective means of control. _If allowed to persist, it can result in deformed foliage. _Seen on: Elm, ulmus

• http://www.king5.com/homeandgarden/ciscoe/10005234_CS0715spitbugs.html
• http://www.laters.com/insects/spitbugs.htm

WEEDS

Whiteflies

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Katrina44

Thanks Matt for the info on pesky pests. But I have a few questions.

What type of bug would be haphazardly eating my maple leaves. Like a few nibbles from this one and a few from that one. They are not skeletonized like with the beetle. I have inspected and see nothing. I even checked in the dark with a flash light one night.

Catepillar? Slug? a vegetarian down on his luck? ;-)

What should I try to eliminate this problem?

thanks

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Kathy
Michigan, USA
Zone 5