How to Kill Whiteflies on Gardenias

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Whiteflies on gardenias are not hard to miss. They will appear in swarms every time you water or walk past your gardenias. They like to hide on the underside of leaves, where they can suck the plant juices undisturbed. They excrete a substance called honeydew, and black, sooty fungus will grow on this substance. Whiteflies multiply rapidly, so it is important to take care of them right away.

Things You'll Need

  • Insecticidal soap, horticultural oil or insecticide
  • Dishwashing detergent
  • Water
  • Natural predators
  • Vacuum
  • Sticky traps
  • Stick
  • Foil or other reflective plastic mulches
  • Petroleum jelly or mineral oil
  • Spray the underside of gardenia leaves with insecticidal soap, horticultural oil or an insecticide such as permethrin. Continue spraying the gardenia plant for several minutes, so you have completely covered it with the soap, oil or insecticide. Spray your gardenia plants every seven days for a month. To make insecticidal soap, combine 2 tbsps. of dishwashing detergent with 1 gallon of water. Do not apply insecticide on hot, windy or humid days, as it will stress the plant more.

  • Buy some natural enemies and place them onto your gardenia plants. Natural predators include minute pirate bugs, lacewings, the Asian multicolored lady beetle and bigeyed bugs, all of which will eat the whiteflies and eliminate the problem naturally. You can find places that sell these predators on the Internet. Your local greenhouse or nursery may be able to order them as well. If you use natural predators to kill the whiteflies, do not use insecticidal soaps as they will kill the beneficial insects too.

  • Locate the heavily infested leaves and remove them. You will be removing the whitefly in its nonmobile nymphal and pupal stages. Do not add the leaves to your compost pile or you will transfer it to other areas of your garden. Throw away infested leaves. If you use pruning shears to cut the leaves off, disinfect them with rubbing alcohol.

  • Alternatively, vacuum the whiteflies from gardenia plants. Do this early in the morning or any time when the weather is cool, when whiteflies are sluggish.

  • You can also place sticky traps around gardenia plants to trap the adult whiteflies. You can purchase sticky traps at most garden stores or make your own by mixing equal portions of petroleum jelly or mineral oil with household detergent. Stick one end of a narrow board into the ground and smear both sides of the board with the petroleum jelly mixture. Check the board occasionally. When it is full of whiteflies and other debris, clean off the board with soap and water. Re-coat the board again with the petroleum jelly mixture.

Tips & Warnings

  • Place foil or other reflective plastic mulches around the gardenia plants. You can also use clear plastic mulch sprayed with silver paint. To use mulches effectively, remove all the weeds around the gardenia plants. This won't kill the whiteflies but will help to keep them away from your gardenia plants.

References

  • Photo Credit Gardenia flower image by Buonfiglio from Fotolia.com
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