Every fall, gardeners bring many plants indoors—geraniums, banana trees, hibiscus, fuchsias, and others—that cannot survive outside in our regions. Unfortunately, they also bring in intruders: small insects and other pests that can damage not only these same plants during their stay indoors, but also other houseplants in the home. Let’s take a look at one of these enemies: the whitefly.
Flying Dandruff
Whiteflies are small flying insects. Adults are white in color and fly freely, but mainly over short distances. They can be seen “flying away” when a plant is moved, only to quickly return to the plant or a neighboring plant: they look like tiny flying flakes of dandruff. On the underside of the leaves of affected plants, you will find not only white adults, but also small translucent “discs”: these are the nymphs (young). They are immobile, attached under the leaves where they lap up the sap that flows from the holes they pierce. This is mainly how whiteflies harm plants, as the loss of sap weakens the plant, slowing its growth, reducing its flowering, and often giving it a yellowish color. In addition, the plant remains slightly wilted, lacking the liquid needed to maintain the turgidity of its stems. Finally, whiteflies can also transmit diseases from one plant to another, particularly viruses.
The most common whiteflies (there are many species, but relatively few live in our regions) multiply in the summer on plants such as Solanaceae (tomatoes, peppers, potatoes, etc.), Cucurbitaceae (cucumbers, melons, squash), beans, fuchsias, and others. Few species can survive a Canadian winter, so they return to the warmth of our homes in the fall when we bring our plants indoors. In the spring, when we take our plants outside again, they follow… and the cycle begins anew.
Discreet in the Fall, Active in the Spring
Whiteflies are very discreet in the fall. The short days and cooler temperatures mean that they do not proliferate much. We only see a few when we bring plants indoors, which gives us a false sense of security. Then, between November and early February, they go into diapause (a kind of hibernation). We no longer see them flying around and it’s easy to think we’ve gotten rid of them. But when the days start getting longer again at the end of February, they wake up and multiply rapidly. Soon, our plants are covered with them and it’s difficult to control them.
What Should I Do?
Be very careful when bringing plants into the house. Wash both sides of the foliage with a solution of water and insecticidal soap. If you still see some, find out which plants are infested and isolate them. The treatment is two-fold: catch the adults and suffocate the nymphs. And it’s best to act now, while they are still few in number.
To catch adults, hang yellow traps (available at garden centers) near affected plants. Whiteflies are attracted to yellow and will land on the trap. Since the trap is sticky, they will remain there. Or paint the end of a handheld vacuum cleaner yellow and run it among the plants. The vibrations scare the adults, causing them to flutter around… and head for the first yellow object you show them: the vacuum cleaner, whose suction picks them up.
But trapping the adults is not enough: the nymphs remain. Spray the foliage of affected plants with soapy water… and repeat both techniques weekly for 3 weeks.
Automated Control
I found an even more effective method, although more expensive: I installed a light trap in my home, such as those sold by catering suppliers to catch flies. The black light it emits attracts adults, and there is a yellow sticky pad inside the lamp: adults that enter never come out! By trapping each adult as it starts to fly, the entire colony disappears.
Good luck in your hunt for whiteflies… and don’t forget to be persistent!
Larry Hodgson has published thousands of articles and 65 books during his career, in both French and English. His son, Mathieu, has made it his mission to make his father’s writings accessible to the public. This text was originally published in Le Soleil on September 24, 2011.
Pesky little things. My greenhouse tomatoes are crawling with them and despite my best efforts to spray, trap and squish them the population is not decreasing by very much. Alas, the tomatoes will be banished to the great outdoors and frost well before they have finished ripening fruit. There is a predator that can be purchased and released to help control them but can be hard to find.