Check gardenia for whitefly before they settle in for summer

Published: Thursday, May 16, 2013 at 16:08 PM.

Treating whitefly

Whiteflies produce several generations each season. If you have them on your gardenia bush now, they will likely persist all summer and into future seasons. On some bushes, whiteflies never seem to get out of hand. This is because their populations are kept in check by beneficial insects, including ladybugs, lacewings, and parasitic wasps. If you find whitefly on your gardenia but it is otherwise healthy with lots of clean, green leaves, you probably do not need to treat. In fact, applying pesticides can disrupt the balance between beneficial and pest insects, causing the pest insects to become the dominant species.

If your gardenia has whitefly, drops lots of yellow leaves and currently or in the past has been covered in black sooty mold, the plant would likely benefit from some form of intervention. There are many options for managing whitefly, including organic and synthetic pesticides. Some gardeners have reported taking their vacuum cleaner or shop vac into the yard and simply vacuuming off the insects. While effective, this method will need to be repeated once a month through the summer, or whenever adult whiteflies are present.

Insecticides that can be used by organic gardeners to control this pest include insecticidal soap and horticultural oil. One benefit of these products is they are less harmful to beneficial insects, as well as being safer for pets and people. To be effective horticultural oils and soaps need to be applied thoroughly to the backs of leaves all over the plant. They will need to be reapplied once a month through the summer.

Synthetic insect control products containing pyrethroid insecticides will also control whitefly, but are very damaging to beneficial insect populations. These include insect killers than contain the active ingredients permethrin, cyfluthrin, bifenthrin, and lamba cyhalothrin. These are sprayed on the leaves and must be reapplied over the summer.

Another synthetic insecticide option is imidaclopyrid, often marketed as Merit. This systemic chemical is applied to the roots, which absorb and move the chemical throughout the plant. The effects last for several months, so this product only needs to be applied once a season. Systemic products like Merit are less damaging to beneficial insects which do not feed on plant tissue, but recent research has shown they can harm pollinators which feed on plant nectar. Always read and follow all label directions when using any pesticide.

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