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Nothing is more maddening for an indoor gardener than seeing their precious houseplants under attack. Here’s advice for dealing with a few of the most common houseplant pests!
Prevention is Paramount
The most important thing to known about battling pests is that prevention is always easier than full-on warfare, so be proactive. Take time to check your plants weekly for unwanted houseguests, paying close attention to the tops and bottoms of leaves. If you find a plant is infected, isolate it from the rest of your collection until you can deal with it.
Additionally, a clean plant is a happy plant, so while you are holding inspection, clean those leaves off. Dust builds up and can block sunlight. Spray them with lukewarm water or a little diluted dishwashing liquid in the sink and rinse them off. Dust plants that don’t like their leaves to be wet with a cloth or soft brush.
Here are five of the worst offenders that have the same modus operandi—they survive by sucking the juices out of the plant—plus a sixth pest that does things a little differently. The juice-suckers exude a sticky-sweet substance called honeydew, which can eventually grow sooty black mold. Pests’ feeding on the plants will cause new leaves to be deformed and growth stunted.
One way to learn what is ailing your plant is to shake it over a piece of white paper and see what falls out. Chances are good that it will be one of these five culprits. Identify them, treat them, and say “so long, suckers!”
1. Mealy Bugs
Mealy bugs look like cottony white specks. The actual insects are pink or pale gray, but they cover themselves and their egg masses with a fluffy white wax for protection. Since they start out small, they can be hard to find, hiding in leaf axils—where the leaves meet the stem, under the leaves, or at the base of the stem.
Unchecked, mealy bugs reproduce rapidly. Eggs hatch in 10 days and the tiny new babies crawl off to find new leaves to suck and lay their eggs on—up to 600 eggs at a time! Eventually, the population gets large enough to overwhelm the plant. Hopefully you will notice them before it gets that bad!
To remove them, wash the leaves and stems with soapy water or spray with insecticidal soap. Their protective wax makes them waterproof, so it will take several washings to get them all off.
Handpick waxy clusters if you can.
Spray with a 50/50 solution of rubbing alcohol and water. You may want to test it on a single leaf first to be sure that a sensitive plant doesn’t react badly to the alcohol.
If a plant is sensitive to the alcohol, try to wipe the clusters away with a Q-tip dipped in alcohol taking care not to get alcohol on the leaves.
Spray with horticultural oil or neem oil to suffocate them.
Keep attacking the pests weekly for about a month to get any newly hatched bugs.
Scale insects look like shiny, tan/brown, oval bumps about 1/8 inch long attached to the underside of a leaf or along the stem of the plant. They multiply fast since the females don’t lay eggs. The babies are born live and crawling. They head off to find a sweet spot to suck on, molt into adults, and develop a shell for protection. They are easiest to kill at the crawling stage and when the new shell is still soft.
Wash them off with soapy water. Scrub them off with a brush if the plant is tough enough to take it.
Handpick them or use a Q-tip dipped in alcohol to rub them off.
Suffocate them with horticultural oil or neem oil.
Treat them two or three times 4-5 days apart to get them under control. Keep an eye out for stragglers and re-treat if necessary. Take it from someone who has been battling them for years. An infestation of scale can be hard to conquer!
Aphids have pear-shaped, soft bodies and come in a range of colors, but the ones on our houseplants are usually green. They are sometimes referred to as “plant lice” and are most often found on tender new growth. Sometimes you won’t see the active suckers but will notice white skins that they have shed. Adults have wings and can fly off looking for likely spots to lay their eggs. Females can also give birth to 3-6 live young a day for several weeks without mating! This causes populations to soar.
Handpick them if you can or bring the plant to the sink and knock them off with a sharp blast of water.
Spray with insecticidal soap, totally covering them.
Use yellow sticky cards to catch the winged adults.
Spider mites are gray/brown, dust-like specks that resemble tiny spiders. They love dusty plants and thrive in hot, dry conditions—sound like your house in winter? Look for webbing where a leaf meets a stem. Yellow or silver mottled dots and patches on leaves are also a sign that they have been feeding there.
Knock the pests off with a sharp stream of water.
Spray with insecticidal soap. Be sure to get the undersides of the leaves where they hide. Repeat weekly for 3 weeks.
Spray with neem oil.
If you see a cloud of tiny white flies when you run your hand over your plants, you’ve got whiteflies. They live on the underside of leaves as a bump that is actually a pupa. It only takes about a month for an egg to hatch, pupate and develop into an adult. They love to suck the juice from new leaves, which eventually turn yellow and drop off.
Rub off eggs and larvae from undersides of leaves.
Spray leaves top and bottom with insecticidal soap weekly for several weeks to get newly hatched crawlers. Eggs are not affected by the spray.
Unlike the frightful five above, fungus gnats are not juice suckers. Instead, their larvae are the culprits, dining on the roots of your houseplants and causing poor growth, yellowing leaves, and even wilt. Like whiteflies, you’ll see a cloud of them fly off when you shake an infested plant. The larvae and eggs thrive in moist soil and are a sign of overwatering.
Cut back on watering! Let the top few inches of soil dry out between waterings.
They like peat, so switch to a peat-free potting soil.
Smother larvae with ½ inch of sand on top of dried soil or by covering soil with plastic wrap.
Water with Bti (Bacillus thuringiensis israelensis) a soil bacteria that kills many types of larvae including mosquitoes.
Use yellow sticky cards to catch flying adults.
To test if your treatments have been effective, place a piece of cut potato on the soil. It will attract any remaining fungus gnat larvae. Throw it out and continue treatment until they are gone. For more tips for dealing with fungus gnats, check out our Fungus Gnat Pest Guide.
Make Your Own Insecticidal Soap
One plant-friendly “pesticide” that you can make at home is insecticidal soap. This soap spray is effective on soft-bodied insects such as the ones listed above. It works by breaking down the protective waxes or oils on the insects’ bodies.
Rather than buy a commercially made product, try this easy homemade version:
Dissolve 1 teaspoon of mild liquid castile soap or liquid dish soap in a quart of water.
Test it on a leaf first to be sure it does not “burn” your plants. Wait a few days and, if the plant looks okay, use the solution to squelch the offending pests!