[Baltimore Sun] Garden Q&A: How do I get rid of mealybugs? Squish, squish
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Q: My alocasia has white bugs on the back of the leaf. What are they, and how do I treat them?
A: Sounds like mealybugs, a common insect pest of indoor plants. As with sap-sucking insects like soft scale and aphids, mealybugs excrete honeydew, which is mostly sugar-water. Aside from the mess and nuisance of honeydew itself, sticky residues on unfurling leaves can cause them to tear or remain stuck together, deforming or damaging the leaf.
There are a few approaches to treating an outbreak. First, quarantine the plant. If you’re not too squeamish, just squish all that you can find either with your fingers or a cotton swab or piece of moistened paper towel.You can periodically repeat this process, being vigilant for a resurgence, or try using an insecticide. Some gardeners use cotton swabs dipped in rubbing alcohol to dab the mealybugs with, and although this does work, too much alcohol can injure leaves too, so avoid spraying it or using on large areas.
Low-toxicity insecticide options include insecticidal soap or horticultural oil. Choose a product labeled for indoor use and follow its instructions carefully. Take note that insecticidal soap usually needs to be mixed with distilled water in order to dilute evenly, if using a concentrate you mix up yourself. Tap water is okay as an alternative, but may compromise its ability to stay well-mixed in the sprayer, causing uneven coverage when applied. Do not substitute household soaps or detergents for insecticidal soap; they can damage plants or simply won’t work as well.
Either of those sprays work on contact, so any mealybugs hiding in plant crevices, under the pot rim, or inside the drainage holes won’t be affected. A repeat application or two (at least) will likely be needed, at whatever interval the label recommends. Often, it’s every 1-2 weeks until the pest is under control.
If a topical spray isn’t cutting it, your only other resort is a systemic insecticide. Few options exist for use indoors, and generally, they use granules that are soil-applied and watered-in, as roots absorb what the granules leach. The benefit of this is that the chemical lasts longer and poisons the mealybugs as they feed, so you don’t need to find them all.
Some mealybugs also infest roots, and getting rid of them is very difficult, though repotting by completely replacing the old potting mix from around the roots is a good starting point. A heavily-infested plant, or one which isn’t getting relief from treatment attempts, should be replaced.
Q: I wasn’t able to plant a cover crop for veggie beds earlier this season. Can I put seed down now?
A: Now is too late for sowing since we have too little daylight for plant growth, not to mention cooling temperatures, even for cool-climate species. However, you can still mulch vegetable beds with fallen leaves, straw, traditional mulch or landscape paper.
Avoid using plant debris from the crops themselves as a mulch alternative, since this can harbor pests and diseases for next year. To be fair, pest insects can also sometimes overwinter in (or under) a mulch layer too, but by incorporating other practices into your garden planning and maintenance, you can balance out potential pest issues with the opportunity to attract beneficial insects that can suppress them for you. Examples include adding some flowering plants to the yard (ideally near the vegetable garden) to feed pollinating bees as well as the wasps, hoverflies, soldier beetles, and other insects that eat pests.
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.
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