Q: I had a lot of mealybugs on my houseplants last spring, so I put them outside, hoping predators would take care of them, or at least I wouldn’t have to deal with them for a while. Now it is getting cold, and I know I have to bring them inside. How do I get rid of the mealybugs and ensure I don’t bring in any new bugs?
A: It can be very hard to do, but unless your infested plants are especially valuable, either monetarily or sentimentally, the best thing to do is to toss them.
Mealybugs, which look like little clumps of cotton threads, are very hard to get rid of. The ones you see can be killed with rubbing alcohol on a cotton swab, but they are also often in hidden spots, like the crotch of leaves or on plant roots. They secrete a waxy substance that coats them, making a shell that is tough for insecticides to penetrate. They also lay hundreds of eggs, so they spread quickly. They are not just a cosmetic problem, as they weaken plants by sucking the juices. Unless they can be controlled, plants continue to decline until the decision to dispose of them is easy, but by that time, you may find your other plants are infested.
The best control is to stop the problem early by checking every new plant for bugs. Washing new plants with a hose or in a sink or shower never hurts, but it doesn’t necessarily make your home safe. Look for the signs of insects with every watering. Also check around the plants. Eggs may be found, or you may see insects heading off to their next victims.
To help manage mealybugs on plants you can’t bear to part with, or before bringing in any other plants from outdoors, wash them with a hose. Use a strong spray to knock the bugs off. Spray all surfaces of the plants with insecticidal soap, which is inexpensive and can be found in garden centers. It is a contact insecticide, which means it needs to touch the bug, so you need to make sure it goes everywhere the bugs could be, including pots and saucers. You can re-use it indoors, and it can even be used on edibles such as herbs that you may grow as houseplants.
Technically, you should slowly move the plants inside so they get used to lower light, but I don’t find it practical. Like some of us, your plants may look a little sad at first, but will recoup once they get used to being indoors.
More information on controlling insects on houseplants can be found at: extension.umn.edu/product-and-houseplant-pests/insects-indoor-plants.
Written by U of M Extension Master Gardeners in St. Louis County. Send your questions to firstname.lastname@example.org.