ASK THE EXPERTS
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24
Maximum Yield USA | October 2015
I hear a lot about whiteflies, aphids and spider mites.
What attracts them? What are the signs to look for?
And how do I solve the problem?
Thank you,
Cris
Cris, you have named three of the most
prolific pests that plague greenhouses
and indoor gardens. These pests feed on
the sap of leaves, so they are considered
“sucking” insects as opposed to “chewing”
insects, which have movable jaws. If it
looks like your leaves are being chewed
on, the pests you are asking about are
not the culprits. If you notice speckled,
mottled, curled or puckered leaves and
fine webbing, then you likely have one of
these pest infestations.
Whiteflies are most often, as their
name implies, white in appearance and
about an eighth of an inch long. They
are found, like aphids and mites, on
the undersides of leaves. With heavy
infestations, you can gently shake the
plant and be greeted with a cloud of
whiteflies. Whiteflies love Solanaceous
plants such as tomatoes, eggplants
and peppers, and are a common pest
of tropical plants as well. The key to
controlling whiteflies is in the frequency
of your chosen remedy, not so much
your choice of application. There is no
pesticide I am aware of that will kill all
of the life stages of whiteflies, meaning
repeated applications will be necessary
since you will not kill their eggs even if
you kill all of the adults.
Aphids are the largest of the three pests
you mentioned and are the easiest to
spot. They feed on almost any kind of
plant. Their damage is usually found on
new growth, and their feeding distorts
leaves, causing them to pucker or curl.
Aphids are fairly easy to control, but
thorough applications are needed.
These little suckers are born pregnant,
so if you miss a few, a few days later you
will have hundreds or thousands show
up again. Aphids can be controlled by a
strong stream of water, insecticidal soaps,
any insecticide containing pyrethrins, or
by releasing predatory ladybugs.
Spider mites, which are not actually
insects, cannot be controlled with
insecticides. They are arachnids, and
their biology is completely different
than aphids or whiteflies. Spider mites
tend to favor outdoor evergreens, but if
you find them indoors, they will feed on
almost anything. They are best controlled
with suffocants, such as horticultural oils.
If you catch them early enough, hosing
your plants down may suffice, but mites
multiply quickly and can cause a lot of
damage in short order. If you see a
small spider where you suspect spider
mites, leave it alone. It is probably
eating some of the mites that are too
small to be seen without the aid of
magnification. To see if you have mites,
take a white sheet of paper and tap the
suspicious-looking leaves or needles
over top of it. The sight of tiny, moving
specks will validate your suspicions.
Best of luck!
Chris Bond
Chris Bond is the horticulturist at Case Western Reserve University
in Cleveland, Ohio, and host of the Keeping it Green radio program. His
primary role is co-ordinator of the university’s Farm Food Program, but
Chris also teaches classes about growing food. His research interests are
sustainable agriculture and alternative growing methods.