In the Garden:
Southwestern Deserts
September, 2001
Regional Report

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326

A tiny whitefly shows up against the vivid green mint.

Pesky Whiteflies

Late summer is the time whiteflies usually appear to suck the juices out of our plants. Some years their numbers are greater than others. I remember one fall when they were so numerous that they would rise up like a cloud of snow from any plant that was brushed against!

I haven't found whiteflies to be prolific this year. However, a caller asked me how to control them as they were taking over the tomato plants that he had nursed through the summer, so it seems worthwhile to provide a few pointers.

Prevention

The best way to prevent any insect infestation, including whiteflies, is to grow healthy plants. Research shows that pests actually seek out stressed plants for attack. Since many plants, such as the above-mentioned tomatoes, are stressed just surviving our summer heat, they become prime targets for pests. Whiteflies are also fond of large-leafed plants such as squash, melons and pumpkins.

Make sure all plants are watered effectively. Water for annuals should penetrate about one foot deep, two feet deep for shrubs and three feet for trees. Monitor your plants regularly, looking for signs of stress such as yellowing, wrinkled, or dropped leaves. Know the difference between beneficial insects and pests.

Monitoring

Whiteflies leave pinprick-sized yellow spots where they suck plant juices. Tapping a branch will cause them to fly up and they can be spotted if numbers are high. Look on the undersides of leaves where the round, immature scale form of this insect is attached to the plant tissue.

Controlling

There's really no chemical pesticide that is effective against whiteflies. Your best bet is to start spraying off plants with a forceful blast of water from the hose as soon as you see signs of these pesky pests. You may need to do this daily. If the problem continues, add one to three teaspoons of liquid dish soap to a gallon of water to make a soapy water spray. Spray early in the morning to lessen the chance of sunburn.

Sticky Traps

Sticky traps, which are pieces of yellow cardboard with a sticky substance, are also effective against whiteflies. They are attracted to the color yellow, fly to it, and get stuck. You can buy these, or make your own with petroleum jelly.


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