Plants inside our homes can become infested with insects just like plants outside in our landscapes. Indoor pest problems can arise anytime, but are especially common this time of the year, when many tender tropical plants have been brought inside for the winter.
When indoor infestations do occur, they can be devastating if not dealt with promptly, effectively and safely.
Indoor outbreaks of insect pests can spread rapidly and cause tremendous damage because of the friendly environment. There is no rain to wash off insects, and the temperatures are mild year-round. also, there are no natural predators indoors to help control insect populations.
Insects can spread rapidly because we often group houseplants together in well-lighted locations close to windows or glass doors. with plants in such close proximity, insects have no problem moving from plant to plant.
We also do our share of spreading pests around by handling healthy plants after we’ve handled infested plants.
Three of the most common insect pests that occur indoors are mealybugs, scales and spider mites. if you can identify these problems in the early stages, you can reduce the amount of damage that occurs and prevent the insects from spreading. Close and regular inspection of your plants indoors is the best defense against insect outbreaks.
Meet the enemy
Mealybugs are small, oval, soft-bodied insects usually less than 1/8-inch long, distinctly segmented and usually covered with white powdery or cottony waxy secretions. they are sucking insects that feed on the plant’s sap, and they don’t move around much on the plants.
They typically occur in groups or clumps. Look for white cottony masses in the growing points of plants, in their crowns, under their leaves and where the leaves join the stem of the plant. Many people mistake mealybugs for some sort of fungus infection.
Plants heavily infested with mealybugs will appear unhealthy. the leaves of the plant may appear shiny and feel sticky, and the new growth may appear weak and deformed. Many older leaves will begin to turn yellow and drop off.
Scales are related to mealybugs and are also sucking insects. they are covered with a dome-shaped waxy coating that is most often white, tan or brown, depending on the type of scale.
Once they are large enough to notice, they do not move. this, along with their waxy covering, makes it difficult to become aware of them, and once you do see the strange bumps or dots on the plant, you would never think that they are insects.
As with mealybugs (and many other sucking insects), plants infested with scale will often have shiny, sticky leaves. even the floor or table the plant sits on may become sticky. this an accumulation of honeydew (a sugary, sticky excretion of the scale) on surfaces under the plant.
If the population of scale insects on the plant passes the plant’s tolerance, the plant will begin to lose vigor, and leaves will yellow and drop off.
Spider mites are related to spiders, but, unlike their beneficial relatives, they are damaging to plants. Spider mites are very tiny (most are not readily visible to the naked eye), and the damage they cause is initially very subtle. this makes early detection difficult, and populations are often out of control and damage extensive before the indoor gardener sees there is a problem.
Initial damage to the foliage causes it to appear dull, faded, stippled and unhealthy. as damage increases, new growth may be stunted and deformed, and older leaves may become very faded, show signs of browning and begin to drop off.
High populations of mites may produce fine webbing where the leaves join the main stem and between leaves.
Take prompt action
These three pests attack a tremendous variety of indoor plants. Virtually every plant we grow indoors is susceptible to one or more of them.
When a pest problem is detected, prompt action is needed.
First, isolate the infested plant or plants. All three of these pests are contagious. always wash your hands after working with an infested plant, especially if you are about to handle healthy plants.
Spraying a plant every day with a strong stream or spray of water (get under the leaves especially) will usually get rid of spider mites.
Continue spraying for at least a week. Indoors, this will work well only for plants small enough to move to sinks or showers. Move larger plants outside to a shady area for treatment (weather permitting).
A strong stream of water can be tried on mealybugs, but you should also scrub at the cottony clusters with a soft toothbrush to dislodge them.
You will commonly see recommendations to control mealybugs with rubbing alcohol applied with a cotton swab. this can work, but it is tedious, and you must treat the plant regularly and persistently over several weeks.
Pesticide use
If you decide to use pesticides, you must choose materials that are labeled for use on plants indoors and are safe to use on the plant you intend to spray.
Do not use sprays that are meant to be applied outside or those for controlling indoor house pests such as roaches or ants.
Mealybugs, scales and mites are all controlled by horticulture oil sprays, which kill these pests by suffocation and are relatively low in toxicity. Look for light horticultural oils such as All Seasons Oil or Year Round Spray Oil.
Many insecticidal soap products also have labels for indoor use and are excellent for mites and good on mealybugs, but not very effective on adult scale. Pre-mixed houseplant insecticides that contain pyrethrum or pyrethrin as their active ingredient would also be effective on these pests.
Use pesticides cautiously, and follow label directions precisely. be prepared to make several applications for complete control.
Since spraying can be messy, particularly when spraying larger plants, move plants outside to treat them whenever it is practical and weather allows.
DAN GILL’S MAILBOX
I have two bougainvilleas in hanging baskets. the plants are about 3 feet across, and the baskets are about 12 inches in diameter. can I cut these back, and, if so, when is the best time?
Diane
The best time to prune bougainvilleas is right after they finish a bloom cycle, although you can prune them at anytime without hurting them. we generally get one to three bloom cycles a year — spring, mid- to late summer and fall/winter. I have some bougainvilleas in a greenhouse blooming now, and many bougainvilleas will bloom in spring if they were kept in good shape over the winter. if it is critical to prune them now, feel free to do so. if you can, however, you might want to wait until April or may to see if they will bloom in spring. if you get a spring bloom, cut them back after they finish blooming. Cutting them back now may make a spring blooming less likely, especially if you cut them back hard. But, again, it will not hurt to cut the plants if you need to.
Is it OK to leave leaves under trees as mulch? do I need to mow them first so the rain gets through? also, I’ve read that the leaf mulch should extend out to the drip line of the trees. do you agree?
George Turner
Having leaves under the tree is not just OK, it is perfectly natural and healthy for the tree, and there is no need to chop them with a mower. Think about it; in the wild, the leaves a tree drops land underneath it and stay there to decay. you will simply be creating a natural situation that the tree will appreciate. the mulch can extend as far out from the trunk as you like. Extending it to the drip line is excellent, if you don’t have lawn grass growing there. Generally, mulches under trees should be no deeper than 4 to 6 inches. Pull the mulch slightly back from the trunk of the tree.
I would greatly appreciate your help in identifying the insect in the attached photo, and your advice on which insecticide I should use to eradicate them from my garden. they seem to damage my hibiscus buds.
Bonnie Rousset
Thank you so much for attempting to identify an insect before you start spraying with insecticides. far too often, gardeners grab insecticides and spray when it isn’t needed. the insect in the photo is our native assassin bug, one of our most common and most valuable predatory insects found in gardens. Please do not spray to kill them. they eat other bugs and are your friend in the garden. the insect in the photo is a nymph, or immature, assassin bug. When they are mature, they continue to have an orange body and long black legs, but they lose the spots and grow black wings crossed over their backs. you may also see clusters of small nymphs on occasion. Siblings tend to stay together for a while after hatching. you will often see them congregated at the tips of branches, waiting and looking for insects to prey on. on hibiscuses, assassin bugs would not damage the flower buds, but rather would likely help to control aphids, an insect pest which commonly infests these bushes.
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Dan Gill is extension horticulturist with the LSU AgCenter.
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Dan Gill, garden columnist
The Times-Picayune Living Section
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