What to Do When Whiteflies are Out of Control

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I’m often envious of gardeners living in temperate climates because they can grow practically anything and enjoy a much longer growing season. But it’s a tradeoff. With the milder weather there are also more potential pests. One we have on a small scale are whiteflies.

I’ll find them on houseplants, which are quickly remedied by putting the whole plant in the shower and blasting it with water. Once in a while, they’ll be on vegetable plants in the garden, but for the most part they’re little more than a nuisance. This is far from reality in other parts of the country, where whiteflies devastate plants and keep gardeners on edge with the risk of potentially losing their crops.

When a plant is infected by whiteflies, it receives a double whammy of problems. Not only do the whitefly adults damage the plant by sucking the juices from them like aphids do; they are vectors of disease. The piercing of the leaves makes the plant vulnerable to infection, plus the honeydew the whiteflies secretes tend to create an ideal environment for fungus.

How to treat whitefly infection

If you live in an area where whiteflies are an issue, you have to start early in the season to identify when the whiteflies are present so you can meet them head on with treatment. If you don’t have time to inspect the underside of the leaves of each plant, place sticky traps in the garden early in the season to keep tabs on their presence. Once you identify that they have arrived, be relentless.

~ Wash them off as often as possible.

This includes the ants. They groom and protect whiteflies just like they do aphids because of the honeydew the whiteflies secrete. Since they’re protecting them from the jaws of the beneficial insects who feed upon them, this is not a good thing, which is why you need to deal with the ants, too. Make up a paste with borax and powdered sugar and feed it to them if you find colonies nearby.

~ If straight water isn’t doing the trick, use insecticidal soap or a horticultural spray.

The soap (not a detergent, that is an important distinction) removes the outer protection of the insects, while the horticultural oil basically smoothers them.

~ Don’t overfertilize or prune.

While you might think keeping the plant healthy and growing vigorously makes sense to battle whiteflies. they absolutely love that yummy new growth. Use a time release fertilizer, like Osmocote, to feed the plants without encouraging rapid new growth. Or, if you’re using a liquid soluble fertilizer, feed on schedule.

~ Try Imidacloprid early in the season before the bees are on the blossoms if you are desperate.

Imidacloprid is a systemic insecticide that affects the nervous system of the pests so when the sap-sucking insect, such as whiteflies or aphids, pierce the plant and ingest the juices they are dosed with the poison. Imidacloprid breaks down rather quickly when exposed to sunlight, but stays in the soil for a prolonged period of time. There’s evidence that it might be harmful bees and other beneficial insects so use it as a last resort.

Whiteflies, like aphids, are one of those pests that aren’t a big deal when you’re dealing with a few, but with long, warm seasons they breed prolifically potentially overwhelming a garden. If you enjoy the benefits of a mild season, be ready for battle.

The photo of the whiteflies on the underside of the basil leaf is by Bildagentur Zoonar GmbH via shutterstock.com.

Meet Amy Grisak

Amy is a freelance author and photographer in Great Falls, MT who specializes in gardening, foods, and sustainable agriculture. She provides information on every kind…

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