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A Closer Look - Bonsai Pests
Part 1, Aphids
Part 1, Aphids
Aphids are a ubiquitous garden variety pest in temperate regions, as irritating on our
tomatoes as they are on our bonsai. Also called plant lice and greenflies, Aphids are part of the
insect superfamily of Aphidoidea (which pretty much covers all of the types of aphids but two),
with over four thousand species known (over two hundred considered pests to horticulturists),
ranging in size from one to ten millimeters. Soft bodied, tiny, and destructive, they are seriously
irritating little buggers that feed on the soft parts of our plants.
Aphids, for the most part, cause damage to our plants in one of two ways: by feeding off of
the sap of the plant, and by potentially introducing viruses to the host plant (though fortunately,
this is more common with vegetables than with trees, phew). The first is easier to deal with by
dealing with the infestation. And, I assure you, if you see a couple aphids now, deal with it,
rather than waiting. A couple aphids might not do much, but if they like your tree, they will
reproduce, and *quickly*.
tomatoes as they are on our bonsai. Also called plant lice and greenflies, Aphids are part of the
insect superfamily of Aphidoidea (which pretty much covers all of the types of aphids but two),
with over four thousand species known (over two hundred considered pests to horticulturists),
ranging in size from one to ten millimeters. Soft bodied, tiny, and destructive, they are seriously
irritating little buggers that feed on the soft parts of our plants.
Aphids, for the most part, cause damage to our plants in one of two ways: by feeding off of
the sap of the plant, and by potentially introducing viruses to the host plant (though fortunately,
this is more common with vegetables than with trees, phew). The first is easier to deal with by
dealing with the infestation. And, I assure you, if you see a couple aphids now, deal with it,
rather than waiting. A couple aphids might not do much, but if they like your tree, they will
reproduce, and *quickly*.
Green Peach Aphids, Myzus persicae.
USDA img #k836-3, used under open source
permission
USDA img #k836-3, used under open source
permission
The green apple aphid (''Aphis pomi'')
*A, adult sexual female *B, adult male
*C, young female *D, female laying an egg
*E, eggs, which turn from green to block after
they are laid. (Enlarged about 20 times)
USDA image from wikipedia, used under open
source permission
*A, adult sexual female *B, adult male
*C, young female *D, female laying an egg
*E, eggs, which turn from green to block after
they are laid. (Enlarged about 20 times)
USDA image from wikipedia, used under open
source permission
Aphid Habits: Some species feed on only one type of plant (these are called monophagous),
though there are others that will feed on a large number of different types of plants (the green
peach aphid, Myzus persicae, as a for instance). They are passive feeders. This means rather than
sucking out the sap of a plant, they use their mouth parts to puncture the phloem of their host
plant, letting the natural pressure within the phloem force the sap out to them. Since the sap of
most plants is relatively high in sugar (a product the aphids don’t need much of) and relatively
high in nitrogen (something the aphids do need a lot of), they frequently give off a waste product
known as ‘honeydew’, drops of sweet liquid containing the sugar they didn’t need. Ants on a
plant can frequently be an indicator of an aphid problem, as ants are attracted to the honey dew.
Some species of ants will even ‘herd’ aphids as food sources, moving them to new plants and
protecting them from predators. When host plant quality becomes poor or conditions become
crowded, some aphid species produce winged offspring (known as alates) that can disperse to
other food sources.
Aphid Reproduction: Interesting note- Aphids give birth to live young, called Nymphs. At least,
some do, others lay eggs. There are also species that can reproduce asexually, which, considering
how invasive these things are and the fact that they can be spread via wind, goes a long way
toward explaining why this family of insects is so darn pervasive. Different species of aphids have
different methods of reproduction, which makes it difficult here to give a brief over view. But the
general gist is that most aphids reproduce rapidly when conditions are right. In the spring and
summer the females (asexually) give birth to live young (all female), some of which may have
wings to help them spread. At the end of the summer, males and females are produced, and eggs
are laid and fertilized from this generation which will hatch the following spring. But in a warm
situation like the tropics or a greenhouse, female aphids can reproduce asexually for years.
though there are others that will feed on a large number of different types of plants (the green
peach aphid, Myzus persicae, as a for instance). They are passive feeders. This means rather than
sucking out the sap of a plant, they use their mouth parts to puncture the phloem of their host
plant, letting the natural pressure within the phloem force the sap out to them. Since the sap of
most plants is relatively high in sugar (a product the aphids don’t need much of) and relatively
high in nitrogen (something the aphids do need a lot of), they frequently give off a waste product
known as ‘honeydew’, drops of sweet liquid containing the sugar they didn’t need. Ants on a
plant can frequently be an indicator of an aphid problem, as ants are attracted to the honey dew.
Some species of ants will even ‘herd’ aphids as food sources, moving them to new plants and
protecting them from predators. When host plant quality becomes poor or conditions become
crowded, some aphid species produce winged offspring (known as alates) that can disperse to
other food sources.
Aphid Reproduction: Interesting note- Aphids give birth to live young, called Nymphs. At least,
some do, others lay eggs. There are also species that can reproduce asexually, which, considering
how invasive these things are and the fact that they can be spread via wind, goes a long way
toward explaining why this family of insects is so darn pervasive. Different species of aphids have
different methods of reproduction, which makes it difficult here to give a brief over view. But the
general gist is that most aphids reproduce rapidly when conditions are right. In the spring and
summer the females (asexually) give birth to live young (all female), some of which may have
wings to help them spread. At the end of the summer, males and females are produced, and eggs
are laid and fertilized from this generation which will hatch the following spring. But in a warm
situation like the tropics or a greenhouse, female aphids can reproduce asexually for years.
Anatomy of an Aphid: Aphids have soft bodies, ranging in color from green, yellow, brown,
black and pink (though green seems to be the most common). Some species may appear waxy or
“woolly”. Their bodies are squat, and frequently pear shaped, with a tail like protrusion (called
a cauda). They have two compound eyes. Aphids have antennae, like all true insects, with as
many as six segments. They feed themselves through stylets, which are the sucking mouth parts
we find so detrimental, which are enclosed in a sheath called the rostrum. They have long, thin
legs compared to their squat body shape and size, with double clawed “tarsi”, which is just a
fancy name for a certain part of an arthropod’s leg. Most aphids have a pair of abdominal tubes
(called cornicles or siphunculi), through which they exude defensive fluids to help ward off
predators. The presence of cornicles distinguishes aphids from all other insects.
Photo by Scott Bauer.
An alate (winged) green peach aphid,
Myzus persicae.
USDA Img #k9602-1, used under open
source permission.
An alate (winged) green peach aphid,
Myzus persicae.
USDA Img #k9602-1, used under open
source permission.
How do you know if you have Aphids: Aphids come in a number of colours and sizes, but all are
tiny, soft, pear shaped bodies with cauda (tail like protrusion) and cornicales (two tubes protruding
from the rear end). If you have an infestation, you’ll be able to see them. You can also look for ants
that are traveling up your plants (they look like they are on a mission, which is pretty accurate
actually). Honeydew, the sweet liquid excreted by the aphids (as well as some kinds of scale) is
another sign. Black moulds can grow on the honey dew, but they are generally considered harmless.
Ugly, but harmless. Aphids leave pretty distinctive signs, even beside themselves. Leaves in an
infested part of a plant will often look wrinkled or folded, even outright distorted. Aphids feeding on
the base of a leaf will cause the leaf to curl backward, folding over them. Flower buds may be
damaged or fall off completely. Some species of aphids will form a gall (an abnormal lump on a
branch) and live inside of it, to help protect them from predators. You may also see yellow, stunted
growth, wilting, mottled and brown foliage. Beside the weakening caused by the removal of sap, some
aphids’ saliva is actually toxic to the plants they feed on.
Aphid prevention: The best prevention for aphids is healthy, happy plants. When plants aren’t
stressed, they have better defenses against infestations. Keep a good distance between your trees to
keep good airflow, adequately water your bonsai, and make sure they are getting the right amount of
light for their species preferences. Don’t over fertilize. Chemical fertilizers high in nitrogen produce
large amounts of just the right kind of growth that attracts aphids and scale. Slower acting, organic
fertilizers are better for helping prevent these infestations. While we go for good growth in our trees,
this is another reminder for us that balance is the key to all things in bonsai. Aphids can also thrive in
thick inner canopies of trees, so keep your trees from getting too over grown in the interior. Allowing
light and fresh air to penetrate will help prevent other diseases as well. There are also some studies
that have been done using reflective mulches (silver coloured polyethylene sheets) to help prevent
aphid infestations, though I’m not sure if anyone has tried them in bonsai cultivation. Keep new plants
isolated for a week or two before putting them near your other bonsai. This way, if there is an aphid
problem you may have over looked at purchasing, you have a chance to catch it before it spreads to
your other trees.
tiny, soft, pear shaped bodies with cauda (tail like protrusion) and cornicales (two tubes protruding
from the rear end). If you have an infestation, you’ll be able to see them. You can also look for ants
that are traveling up your plants (they look like they are on a mission, which is pretty accurate
actually). Honeydew, the sweet liquid excreted by the aphids (as well as some kinds of scale) is
another sign. Black moulds can grow on the honey dew, but they are generally considered harmless.
Ugly, but harmless. Aphids leave pretty distinctive signs, even beside themselves. Leaves in an
infested part of a plant will often look wrinkled or folded, even outright distorted. Aphids feeding on
the base of a leaf will cause the leaf to curl backward, folding over them. Flower buds may be
damaged or fall off completely. Some species of aphids will form a gall (an abnormal lump on a
branch) and live inside of it, to help protect them from predators. You may also see yellow, stunted
growth, wilting, mottled and brown foliage. Beside the weakening caused by the removal of sap, some
aphids’ saliva is actually toxic to the plants they feed on.
Aphid prevention: The best prevention for aphids is healthy, happy plants. When plants aren’t
stressed, they have better defenses against infestations. Keep a good distance between your trees to
keep good airflow, adequately water your bonsai, and make sure they are getting the right amount of
light for their species preferences. Don’t over fertilize. Chemical fertilizers high in nitrogen produce
large amounts of just the right kind of growth that attracts aphids and scale. Slower acting, organic
fertilizers are better for helping prevent these infestations. While we go for good growth in our trees,
this is another reminder for us that balance is the key to all things in bonsai. Aphids can also thrive in
thick inner canopies of trees, so keep your trees from getting too over grown in the interior. Allowing
light and fresh air to penetrate will help prevent other diseases as well. There are also some studies
that have been done using reflective mulches (silver coloured polyethylene sheets) to help prevent
aphid infestations, though I’m not sure if anyone has tried them in bonsai cultivation. Keep new plants
isolated for a week or two before putting them near your other bonsai. This way, if there is an aphid
problem you may have over looked at purchasing, you have a chance to catch it before it spreads to
your other trees.
Aphid Removal: If despite your best efforts, you notice an aphid infestation on one of your trees, don’
t panic! There are several steps you can take, ranging from the simple to the more complex.
The simplest, and cheapest way to deal with a mild aphid problem is to spray the entire plant with
a strong burst of water to knock the aphids off. Make sure you get everywhere, especially the bottoms
of the leaves and branches where the aphids might hide. Remove any leaves that have curled in on
themselves, as aphids will hide in these as well. Don’t just knock them on to the soil beneath your
benches though, as they will just come back. Find someplace out of the way or over a drive way where
you can then wash the whole thing down again. Spray your plants early in the day so they have a
chance to dry and you can check them again in the afternoon. A solution of soapy water can also be
used to wash over the entire plant.
t panic! There are several steps you can take, ranging from the simple to the more complex.
The simplest, and cheapest way to deal with a mild aphid problem is to spray the entire plant with
a strong burst of water to knock the aphids off. Make sure you get everywhere, especially the bottoms
of the leaves and branches where the aphids might hide. Remove any leaves that have curled in on
themselves, as aphids will hide in these as well. Don’t just knock them on to the soil beneath your
benches though, as they will just come back. Find someplace out of the way or over a drive way where
you can then wash the whole thing down again. Spray your plants early in the day so they have a
chance to dry and you can check them again in the afternoon. A solution of soapy water can also be
used to wash over the entire plant.
My personal favorite (an a preventive measure I take almost every year anyway) is to release insects that feed on aphids in to my garden
and amoung my bonsai. The most common are lady bugs, though there are also types of parasitic wasps, aphid lions, crab spiders, syrphid flies
and lace wings amoung others. These beneficial insects will stick around as long as there is food (i.e. APHIDS!), but you can encourage them to
stick around longer by planting certain things that attract them (yarrow, cilantro, parsley and sweet alyssum are all plants that lady bugs in
particular like). Lady bugs can be purchased at most garden centers now, as an alternative to chemical pesticides. If you are going to try
beneficial insects, make certain you don’t use any pesticides, as these will kill the good bugs as well as the bad.
Insecticidal soap or neem oil can be used, and is generally safe for bonsai, but check the label, and if in doubt, do a test on a small portion
of the plant to be certain it does not cause an ill effect. An even coat that gets every part of the plant (especially the underside of the leaves!) is
necessary. These only work on contact, and do not provide long term prevention. If a spot is missed on the plant, the infestation can balloon
again once the oils have dried, and applications may need to be repeated. Do not use oils on water stressed plants (those that have been under
watered and have wilted, or those that have been over waters and may have root rot), or if the weather exceeds 90F (30C), as this can harm
the plant. Supreme- or superior-type oils will kill overwintering eggs of aphids trees if applied as a delayed dormant application just as eggs
are beginning to hatch in early spring. These treatments will not give complete control of aphids however, and additional controls may be
needed later in the season. Earlier applications will not control aphids.
There are also many other, stronger insecticides available for aphids (malathion, permethrin and acephate to name a few). Some of these
are safer for bonsai than others. Especially if a certain tree is hit consistently by aphid infestations, a systemic pesticide might be worth
considering. Maples and Elms in particular can be susceptible to repeat attacks. There are so many kinds available it is hard to go over all of
them. General guidelines are to follow the instructions on the bottle for usage, including timing and dosage. If in doubt, test it on a small area
of the tree. If there are no negative affects (dying leaves, blackening bark), you can probably proceed with the rest of the tree. If you can,
however, avoid the use of diazinon and chlorpyrifos; beside diazinon being dangerous for a few species we use for bonsai, both have been
identified as serious sources of pollution in lakes and rivers. Carbaryl is not recommended because it is not very effective against aphids. In
general, check the labels and see what pests they are effective against.
Keep in mind that if you see ants in conjunction with the aphids, you also have to deal with the ants, as they will simply re-infest the plant.
If they have made a nest in the pot itself, repotting and making sure to remove all of the old soil is effective. There are also some insecticides
useful against ants, but many are not, so be certain to read the labels. Smaller garden centers can often lead you in the right direction for which
pesticides will be the best for your area.
******
On large, landscape trees, Aphids are seldom a problem. But on small bonsai with limited roots, they can weaken a plant quite a bit, and
even lead to death if not taken care of. While it may seem simple, or even not very worrisome if you see only a couple aphids, whether on a
bonsai or another garden plant, early reaction and prevention are your best defenses again a full blown infestation.
Photo by Scott Bauer.
A P-14 lady beetle (Propylea
quatuordecimpunctata) devours a pea aphid.
USDA Img #k5812-17, used under open
source permission.
A P-14 lady beetle (Propylea
quatuordecimpunctata) devours a pea aphid.
USDA Img #k5812-17, used under open
source permission.