Even though Petunia doesn’t “do” gardening, she does have a plethora of house plants. Most of them spend a vacation outdoors for the summer under various trees. She religiously hoses them off before she brings them inside, but every year she must fight various insects that have hitchhiked inside.
These pests can be blown into a house, come through the screens, been on the plants as eggs, or hitchhiked in on that live Christmas wreath or even come in with the live Christmas tree. However gotten, some are now inhabiting her plants. The pests can be mealy bugs, white flies, thrips, spider mites, aphids, or scale.
You can use several methods to look for these stinkers. Look over the plants especially under the leaves with a magnifying glass. Set out yellow sticky traps. You can make these yourself. Glue a bright yellow piece of cardboard, about 2-by-4 inches big, to a stick. Then coat it with anything sticky; honey, or the sticky bird repellent you use to keep woodpeckers from destroying your trees. Two-sided tape works well too. Check your traps every day. Be sure what you are looking at isn’t just a hunk of dust before you get handy with the spray. That long bit is probably cat, dog or your hair as none of these bugs are that shape. These sticky traps may improve your housekeeping if you find more dust than bugs on them. Check your plants for yellowing or browning leaves. This can indicate several things other than bugs. To check for spider mites, hold a white sheet of paper under the plant then shake the plant. They are bright red and very visible. They will also leave webs on the plant just like their big sisters.
If you notice browning or yellow leaves, the plant may be overdry, too wet, too shaded or just dropping leaves because the light is not as bright as it had been outside. Do your Sherlock thing and look at the leaf with your magnifying glass to be sure it is infested, not just unhappy. Do treat any infested plants right away. You don’t want the plant so sick you need to give it a vacation on the porch in below-zero weather. (It does kill the bugs). You can usually get rid of a slight infestation by wiping the leaves with a paper towel or cloth dipped in alcohol. This doesn’t mean vodka, use rubbing alcohol. Save the vodka for afterwards. You can also try a ½ teaspoon of mild dish soap in a quart of water to wipe off small numbers of bugs. If just a few leaves or branches are buggy, just remove them. Or you can use insecticidal soap. One lady brought a plant into the Extension office that had white stems and leaves. It was totally covered with scale. There was no saving that poor thing. Scale is very hard to kill as it has a hard coat and sticks tightly to the plant.
Three companies, Bayer, Schultz and Bonide all sell sprays for houseplant insects. Check the labels for a list of the bugs it kills. The sprays have a residual that may be as short as one day. Both Bayer and Bonide have systemic insecticides. That is, they are taken in by the plant, so all the plant is poisonous. There is a note that the Bonide Systemic Houseplant Insect Control granules are really stinky and should only be used if the plant is actively growing. You apply them to the soil.
Here’s to Petunia’s bug-free house.
Bev Johnson is a Master Gardener with the University of Minnesota Extension. Her column appears in the Weekend Edition.