By Jim Lakin, MD, Master Gardener
Last month we talked about keeping your houseplants healthy, paying attention to growing requirements, fertilization, watering, hygiene and potting soil. Minding all these factors will reduce the chance of sickly plants and pest attacks. Yet, alas, in even the best of environments, insect problems sometimes rear their ugly heads. So, what to do if you suspect you have some unwelcome residents on your houseplants?
As we said, inspect them for insect pests when you water, clean or fertilize. They most often congregate on the underside of leaves. You should look for insects, holes, webbing or eggs. Give an even closer inspection to any plants brought in from the store or the outside. Using a magnifying glass helps. It also impresses any bystanders. You want to look for “honeydew” which is a shiny sticky substance produced by aphids, mealybugs and scale insects. Also check plant containers for pests along the ridges and bottom of pots and saucers. It’s not a bad idea to put a new plant in quarantine, away from the rest of your collection, for a week or two. More often than not a pest problem will declare itself during this period.
When you water the plants keep a sharp lookout for bugs like springtails and fungus gnats. They usually move with the water. If you think you might have flying insects like thrips, winged aphids, fungus gnats or whiteflies, setting up a sticky paper trap like the one illustrated can help in detection.
If you find an infestation early on, more often than not you can manage it without pesticides. That’s good for you and for the environment. Washing the plant will remove small infestations. Use a paper towel to wipe leaves, changing the paper frequently to prevent spread. You can wash small plants in the sink and larger ones in the shower. Be one with your Ficus!
You can physically remove many pests. Larger insects such as millipedes, slugs, caterpillars or earwigs can be picked off the plants. Mealybugs can be removed with a forceps (tweezers) or a cotton swab dipped in alcohol. Those hard little grey scales can be taken off the plant with a fingernail file.
Pruning is another option if the critters are isolated on a few leaves, stems or branches. Be aggressive. Most plants will recover remarkably well if relieved of their insect burden and given the right growing environment.
If all else fails and the plant looks like a goner, don’t hesitate to toss it. This avoids exposing other plants to the same pest problem, which will save you grief in the long run. Rather than composting the diseased plant, I prefer to wrap it in a Ziplock bag and put it in the trash.
To obtain more information about specific pests as well as what to do if non-chemical methods fail to control your problem, check out Prof. Jeffery Hahn’s recommendations on the University of Minnesota Extension website: https://extension.umn.edu/product-and-houseplant-pests/insects-indoor-plants#using-pesticides-for-pest-management-1580961