The Q&A Archives: Whiteflies on Tomatoes

Question: I planted tomatoes this summer for the first time and had great success, no doubt due to the hot, sunny summer we had. However, we now have an infestation of tiny white flying insects that fly up by the hundreds when you touch the plant. There are also teeny black dots on the leaves, perhaps the eggs? What is this insect, is it a pest, and, if so, how do we control them?

Answer: It sounds as if you have whiteflies, which often show up late summer or early fall. They multiply rapidly when temperatures are warm, but will die off as cold approaches. They such the juices out of foliage, leaving behind tiny yellow spots, called stippling, which can weaken the plant. The best way to keep whiteflies at bay is to start early. Next year, monitor your plants carefully and when you first notice the whiteflies, start the following control methods. You can still apply these methods this year, as well.

Start with the simplest method first, and if that isn't successful, move on from there. A strong blast of water from the hose often works. Spray underneath leaves where the whiteflies tend to cluster. Do this daily if you notice insects.

Whiteflies are attracted to the color yellow. You can purchase or make yellow "sticky" traps from yellow cardboard smeared with petroleum jelly. They fly to it and get stuck.

Soapy water sprays are another possibility. Use 1 teaspoon to 2 tablespoons of liquid soap per gallon of water. Use regular, not concentrated soap. Don't use soaps with lemon, as the citric acid can burn plants. Start with the lower amount and work up as needed. Spray as often as needed. As with any spray you might wish to test it on a few leaves first before you treat all your plants. Spray early in the morning before the sun heats up.

Next on my list would be an insecticidal soap spray. The insecticidal soaps are made from plant-derived fatty acids and target soft-bodied insects. Unfortunately, there's really no way you can target the bad guys without at least some effect on the good guys. If you can regularly monitor and tolerate some damage to your plants, over time Mother Nature strikes a balance, with the beneficials coming in to control the bad guys. Healthy, vigorous plants will withstand insect attacks better than weakly growing ones, so providing the optimal growing environment is the first step in preventing prevent insect problems.

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