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Houseplant Pests
APHIDS
Aphids, often called plant lice, are tiny soft-bodied
pear shaped insects that can be black, yellow, green, or brown. They are often inconspicuous until large colonies have formed.
Unlike most insects, aphids are mostly female, can reproduce without mating, and give birth to live insects not eggs. Females
can produce up to 100 daughters in a lifetime and these daughters are capable of reproducing within 6-8 days of their birth.
Aphids cause damage by sucking the sap out of a plant; they especially like stems, new growth, the underside of
leaves, and flower buds. This sap removal causes curling and crinkly leaves and ruins flower buds. Aphids also act as a vector
in transmitting viruses from plant to plant. Like mealy bugs, aphids secrete a sticky waste product called “honeydew.”
This honey dew acts as breeding ground for sooty black mold and attracts ants. Black mold disfigures a plant, retards growth,
and prevents photosynthesis.
Aphids are difficult to see and reproduce rapidly so check your plant weekly to prevent
a major infestation. If aphids appear on a leather leafed plant, the green solution or neem oil sprayed on every surface of
the plant should get rid of them. On furry leafed plants use only a mixture of warm water, a few drops of mineral oil, and
a few drops of liquid dish soap. The alcohol in the green solution ruins furry leaves. Spray every 6-8 days for a month to
catch the new aphids as they are born.
Ladybugs voraciously feed on aphids and I have used them in my greenhouses
to biologically control these pests when there is widespread contamination. This is not practical for household use.
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| Photo by Jack Kelly Clark, University of California |
FUNGUS GNATS
This small dark skinny pest flies and jumps around
plants and people driving us all crazy. It does no serious damage to plants but is really quite a nuisance. They develop in
the potting soil feeding on root hairs and emerge as adults every 30 days. The best way to get rid of them is to allow the
soil to thoroughly dry out. This will kill all of the eggs and gnats in the pot. Use yellow sticky cards to trap the fungus
gnats that are flying around.
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MEALY BUGS
Mealy bugs are one of the most annoying and destructive pests
that attack houseplants. These tiny sucking insects look like small pieces of cotton on your plant. When young, mealy bugs
have legs and can crawl. A female mealy bug can lay over 500 eggs all over a plant within a 1-2 week period. This is the best
time to treat an infestation.
Mealy bugs suck the sap out of a plant, concentrating especially on the tender new
growth; this causes leaf spotting or yellow leaves, weakens new growth and stems, and may result in leaves falling off. While
feeding on the plant, mealy bugs secrete a sticky substance called “honeydew.” Honeydew acts as a breeding ground
for “sooty mold.” This black mold covers leaves and stems ruining the plant’s appearance and interfering
with photosynthesis.
When the mealy bugs are immature and crawling, yellow sticky cards can be used to trap them.
Once the eggs have been dispersed throughout the plant, both sides of all leaves, stems, and especially new growth should
be sprayed with the “green solution.” Be sure the plant is well watered and not in the sun when you spray; and
search out all areas where the pests might hide. If the plant has furry rather than leathery leaves use a solution of warm
water mixed with a few drops of mineral oil and a few drops of liquid dish soap instead of the green solution. Repeat this
treatment every 10 days for a month to catch any further eggs that might hatch.
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| Copyright Karsten Dorre (GNU) |
SPIDER MITES
Spider Mites, a member of the Acari family,
are small insects about 1mm in size. The most common indoor houseplant pest is the red spider mite (also called the two-spotted
spider mite.). These pests lay their eggs on the under surface of leaves and produce a profuse fine webbing. Spider mites
are very hard to see with the naked eye, and may appear only as small red dots. They are more often recognized by the gritty
feel of the leaf when you run your finger down it’s length, or by the appearance of discolored leaves due to the sucking
action of the mites.
The best way to prevent mites is to keep your plants clean and dust free.. If mites do attack
your plant, spray every 10 days for a month with the green solution. If the spider mites still persist, purchase a commercial
miticide from your local nursery.
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| U.S.Nat.Collection of Scale Insects Photographs, USDA, Bugwood.org |
SCALE
Soft brown scale is the most common scale that attacks indoor houseplants
especially ficus, ivy, spider, ferns, aralia, and schefflera. It appears as small bumpy brown spots that don’t even
seem to move. As the scale sucks on the sap of the plant it secretes a sticky substance called honeydew. This honeydew attracts
a black mildew called “dusty mildew” that further detracts from the appearance of the plant. Because of their
shell like exterior, sprays are only partially effective against scale. Wipe off the lines of brown oval bumps with your finger,
a cloth, or a child’s toothbrush then spray with Neem Oil. You can use the green solution to clean the dusty mildew
off of the plant.
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| Picture by Jack Kelly Clark, University of California |
THRIPS
Thrips are tiny winged brown insects that feed
on the surfaces of plant leaves, flowers, and buds. They leave silver spots around their feeding areas and dark dots of excrement.
Thrips not only weaken plant growth and distort buds and flowers; they transmit viruses from plant to plant as they fly around.
The green solution, neem oil, and yellow sticky cards all are effective in eliminating thrips.
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| Photo by Jack Kelly Clark, University of California |
WHITEFLIES:
This is a small gnat like insect that is covered in a powdery white wax. Whiteflies
suck the sap from plants. This causes leaves to drop off and weakens the plant in general. They secrete a sticky substance
called honeydew while they feed. The flying adults lay eggs on the tops of leaves, but it is the immature nymph stage, feeding
unnoticed on the underside of the leaves, that does the real damage. Yellow sticky cards are a good way to trap the flying
adults and prevent new eggs. Shake the plant every day to stir them up so they will fly into the cards more easily. Spray
the green solution to get rid of the feeding nymphs on the underside of the leaves.
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