Homegrown: Pests on houseplants

Linn County Master Gardener, Jane Schildroth, explains what to look for, and how to look for pests on houseplants.

By now, houseplants that have been moved inside have had some weeks to acclimate to their new light, air flow and heat conditions, so it's time to give them a good “once over” to check for insects.  Even if they didn't move outdoors and rather spent the summer on a porch with screens, tiny critters may have moved through screens and open windows.  The sooner you discover them on your plants and take action, the better success you will have in conquering them.

If you're buying a new plant from a store, check it very carefully before you bring it home and then place it in isolation from others for two or three weeks.  Choose plants that are appropriate for your light conditions because if they are weak from poor lighting, they are more susceptible to insect damage.  When cleaning your home, forget the feather duster around your plants.  It can become a vehicle for transferring tiny mites or eggs from one plant to another.  If the plant has smooth leaves, wash them regularly to prevent dust from accumulating.  Use a smooth, moist cloth on the leaves and stems.  If there are many small leaves, spray with lukewarm water.  You can also wrap foil over the soil and tip the plant into a tub of water with a few drops of dishwashing liquid. (1/2 teaspoon per quart of water)  Swish it around a bit to give it a good bath!

When re-potting, use sterilized potting soil.  Check every time you water, inspecting tops and undersides of leaves.  You are looking for speckling or mottling – and hoping to find neither!  A magnifying glass will help you find tiny pests, eggs and cast skins.  Also watch for honeydew, a shiny, sticky substance secreted by aphids and scale insects.  It will show up on leaves and also on table tops and anything else located under the plant.

In addition to the washing method mentioned above as a preventative measure, you can do the same for treatment.  Or, you might be able to simply remove the offender with your fingers, a fingernail file or pen knife.  Or, set the pot in a tub of water to saturate it and drive worms to the surface.  If the problem seems to be affecting a few leaves or branches, try pruning those to make it easier to treat the remaining plant.

If you still have insect problems after trying these non-chemical options, you may need to consider using an insecticide.  Find the appropriate one at a nursery, garden center or variety store.  These are usually aerosols or ready-to-use liquid products.  Read the fine print carefully – some products may not be safe for your particular plant.  For a comprehensive list of pests and the active ingredients for treatment, go to https://store.extension.iastate.edu/ItemDetail.aspx?ProductID=5100.  Mix these products carefully and spray thoroughly in a well-ventilated area.  Be sure to spray under the leaves and keep the plant away from direct sunlight for a least a full day after you have treated it.

The last treatment option is called “giving up.”  Sometimes it's just best to cut your losses and save your other plants.  If you can't handle this option, take the pruning to extremes and cut the plant practically to the soil.  Watch to see what happens if it re-sprouts.