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Friday, June 26, 2015

What's wrong with my plant?

“My string-of-pearls plant feels sticky and has patches of what looks like white fuzz on it. What’s wrong?”

Looking through several books, including David V. Alford’s Pests of Ornamental Trees, Shrubs, and Flowers, The Organic Gardener’s Handbook of Natural Insect and Disease Control, and Insect Disease and Weed I.D. guide, we diagnosed the plant with mealybugs. Female mealybugs are covered with a fluffy white wax, and they lay their eggs in similarly fuzzy-looking white wax sacs. (The male insects have wings and are small and difficult to see.) Mealybugs eat sap and secrete something called honeydew, which gives the plant a sticky feel. (Ants also like to eat the honeydew, so a mealybug infestation may give way to an ant infestation.) According to Pippa Greenwood’s Pests and Diseases, succulents (like the string-of-pearls) are some of the most common mealybug hosts.

Our gardening books provided a wealth of ideas for combating the infestation. Debra Lee Baldwin’s Succulents Simplified suggests moving the plant away from any others to somewhere with good air circulation and spraying it down with a mix of isopropyl alcohol and water until all the bugs are gone. Introduce ladybugs, parasitic wasps, or mealybug destroyers, if possible, as they’re all some of the mealybug’s natural predators. Commercial pesticides are also available. If a spray doesn’t seem to be penetrating the mealybugs’ protective waxy coating, try using a small paintbrush to dab it directly on them. The Plantfinder’s Guide to Cacti and Other Succulents by Keith Grantham and Paul Klassen and Cacti and Succulents by Hans Hecht both suggest painting the mealybugs with denatured alcohol or an alcohol/dish soap mixture to remove the waxy coat. Leaf shine spray is also effective against mealybugs, but it will also remove the pleasant powdery bloom on any plant with glaucous leaves.

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