How to Take Care of Indoor Plants: Pest and Disease Management

During late spring and summer, when plenty of general insect predators and parasites are found in the garden, putting the afflicted plant outdoors for several weeks may take care of the problem. Either the pests will be consumed, or, as with migratory aphids, the summer generation may fly away to another host.

How to Get Rid of Aphids on Houseplants

Twice a small hot pepper plant that grows indoors on our kitchen windowsill and provides us spices for chili and beans has been infested in the early spring with an aphid (Myzus persicae). Infestation became obvious because the aphids’ honeydew (the sweet, sticky sugar protein excreted by many plant-sucking insects) began to shine on the leaves. We usually squished the first few aphids by hand, but invariably the aphid population escaped this control measure and began to spread. Usually by this time, the weather had become so mild that the plant could be set outside in a protected sunny spot on the porch. However, the aphid parasites and predators had not arrived in the area yet, so the pepper plant had to be hosed off vigorously each week. If this was not done, the plant began to turn yellow and drop its leaves. As the season progressed, the biological controls appeared. First we would notice parasitized aphids among the colonies; then we would see syrphid fly larvae and adult lady beetles consuming their share. By early summer not an aphid was to be seen. Apparently all had either been eaten by insects or flown off to other hosts. The plant was then promptly moved back into the kitchen, where it lived without apparent insect companions until another spring. How did the aphids get there each year? Since there are a couple of early spring aphids in our area that can live on more than one species of plant, it is easy to see how a winged one might fly or be blown in through an open window or door.

Several years ago, aphids got started on this same plant quite late in the spring, and soon after we noticed their presence parasitized individuals became apparent. Not only had the aphid found its way into the house, but its parasites had too. Since none of the parasites’ parasites found the plant, the parasite proceeded to wipe out every last aphid, ending the problem for that year without our having to move the plant outdoors. But that event has not been repeated, perhaps because we are reluctant to leave the kitchen window open without screens because of house flies.

When moving plants infested with honeydew producers outside, you might wish to place them on stands with ant-excluders around the legs so that ants don’t prevent the aphid predators and parasites from doing a good job.

For bug-infested plants that are too large to move, handpick, or hose off, you can import predatory lacewings or mites just as in greenhouse pest management. After cleaning up the pest insects the predators will die off from lack of food, so for each new outbreak new predators will have to be imported. An excellent book on using biological controls on houseplants is Windowsill Ecology, by William Jorden.

What about using synthetic commercial poisons on house plant bug problems? We have expressed our thoughts on pesticides elsewhere [in this book]. If you feel that a plant is so valuable that it must be saved at all costs, and have exhausted all safer methods of insect management, then be sure to select the least toxic material that will do the job. Move the plant outdoors, and wear a mask and gloves while handling the poison and treating the plant, washing yourself and your clothes afterwards. Remember, the house plants are supposedly being kept to increase your pleasure and health, not to add one more touch of poison to an urban environment already burdened with substances toxic to humans.

Want more on garden pests? Check out the MOTHER EARTH NEWS Organic Pest Control Series.

How to Take Care of Indoor Plants: Plant Disease Management

When plants look sick, and no insect can be found, the usual assumption is that it is being attacked by a pathogen. Plant diseases are harder to cure than either insect infestations or salt build-up (Another occasional threat to house plants–guests surreptitiously dumping unwanted alcoholic drinks into the nearest greenery–will not be dealt with here.) Read “Preventing Plant Disease” further along in this article as a handy checklist.

A last thought on maintaining house plants: They do grow best with attention. Whether this is a response to increased carbon dioxide from human respiration, to the caretaker’s alertness with respect to watering, bug management, and repotting needs, or to some relationship between humans and plants not yet satisfactorily explained, the authors are not prepared to guess.

Learn more about how to have thriving houseplants in our podcast episode, “Where to Put House Plants so They Thrive.”

Preventing Plant Disease

1. Do not overwater.
2. Do not overfertilize. (Excess nitrogen may encourage aphid infestations indoors as well as out, in addition to creating weak, over-fertilized succulent plants more susceptible to disease.)
3. If you or experts you are able to ask for advice cannot diagnose the ailment, try repotting the plant in fresh material.
4. Leaves infested with mold or fungus leaf-spots can be cut off and composted. Necrotic (black) areas on cactus can be cut out with a sharp knife. The cut area should be dusted with sulfur and the entire plant left to dry, out of direct sun, in a light, well-ventilated place until the wound has calyxed over.
5. Where crown-, stem-, or root-rot is the problem, it is best to destroy the plant. Avoid the problem in the future by not overwatering or overfertilizing, and by keeping water off susceptible plants.

Read more: Check out Is the Deep Litter System Right for Your Homestead? for more from The Integral Urban House.

This excerpt has been reprinted with permission from The Integral Urban House: Self-Reliant Living in the City, published by New Catalyst Books, 2008.