Last year we had a dining room full of insects after bringing the houseplants back inside. My cats enjoyed batting at the white flies, but left the leaves pretty ragged. Any tips on avoiding gate-crashers this year?
Get rid of those mooching plant suckers before you bring your tender babies in. Put on your dog -washing clothes and give your plants a good outdoor shower. I like to work on a plastic tarp (so I don't get grass and mud all over the containers). Lay your plants on their sides and rinse them thoroughly, being especially careful to spray under the leaves where whitefly eggs and nymphs will be.
After the plants dry, you can follow up with insecticidal soap which only works if you spray it directly on the insects; it has no residual activity. You need to spray on top and under every single leaf, on the stems, the soil surface, and the pot itself for good control - definitely an outdoor or bathtub exercise.
Avoid the temptation to "save" money by using your neighbor's recipe based on dishwashing liquid; the products labeled for use on plants have been tested and give you the exact concentration to control insects but not burn your leaves. Always read the label completely as there are some plants that seem like they'd be tough as nails that absolutely hate to take a bubble bath and cannot be treated with this product. After several hours you can rinse the soap off treated plants - the soap kills only on contact. If the label recommends re-applications, follow the guidelines if you didn't get complete control with the first spray.
Our erratic temperatures are really your friend when it comes to houseplant pest control. We have at least a month or so before we won't get a warm day when you can tote those plants back out for another treatment if needed. Use tepid water from inside for mixing so you don't shock your plants with what comes out the hose even on a pleasant day.
For really tough infestations, there is a systemic product now labeled for use on container plants. Many gardeners have relied on a Bayer Advanced product to control white flies on their gardenias and other shrubs. The new formulation, Bayer Advanced Tree and Shrub Protect and Feed, is also labeled for use on container plants, with exact measurements for one gallon and up size pots.
This product is applied once a year, absorbed by the plant's roots, and then distributed throughout the entire plant. When whiteflies, scales, mealy bugs and certain other pests feed on the plant sap, they ingest the active ingredient and are killed (or suppressed). Always read the label completely before using this or any other insecticide. If you have a plant that always requires hours of cleaning with alcohol and Q-tips (another tried and true procedure), you may want to give this systemic product a try.
Insects are only one trial that houseplants contend with. Two-legged owners who over water and forced air furnaces can be just as damaging. Please visit Clemson's Home Garden Information Center and read their fact sheets, Indoor Plants - Moving Plants Indoors & Outdoors and Common Houseplant Insects & Related Pests so your indoor plants look like runway models and not refugees from the discount shelf.
Amanda McNulty is a Clemson Extension agent in Sumter County. She will answer your gardening questions in this twice-monthly column. Send your questions to firstname.lastname@example.org