Whiteflies, or white bugs, may be very tiny insects, but swarms of these soft-bodied, winged bugs can quickly pose a major threat to tomato plants in greenhouse and outdoor settings. Fortunately it is possible to manage most infestations by combining close monitoring, early intervention and employing the appropriate control methods.
Whiteflies are diminutive garden pests that belong to the same family of insects as aphids, scale and mealybugs. They are no larger than one-sixteenth of an inch long and look very similar to moths. The most common types of whiteflies are silverleaf and greenhouse varieties. Both types are prolific and since the females can lay up to 400 eggs at a time, populations can quickly spiral out of control without intervention and cause massive damage to tomato plants and other members of the nightshade family.
Female whiteflies lay between 200 and 400 conical eggs on the undersides of tomato leaves. Within about 10 days the legless nymphs hatch. Nymphs initially look like scale insects and are often mistaken for them by gardeners. They go through a series of molts and a pupa stage before reaching maturity. An adult whitefly will live for about a month. Both nymph and adult whiteflies suck the sap from the stems, leaves and buds of the tomato plant, causing it to wither and ultimately die.
Signs of Damage
Plants that have been damaged by whiteflies will show signs of withering and often have yellow leaves. New plant growth is quite stunted and fruit is often misshapen or deformed. And because whiteflies excrete a honeydew-like substance, tomato plants can also suffer from additional maladies including mold and sudden onset of viral infections or disease. Tomato plants that show significant signs of illness or disease should be removed straight away to prevent spreading to healthy plants.
Preventative Methods and Monitoring
Regularly monitoring your tomato plants for whiteflies is one of the best methods for preventing an all-out infestation. Check not only the exterior of the plant, but also the stems and undersides of the leaves for signs of eggs and nymphs as well as adult whiteflies. And if you opt to purchase tomato seedlings or plants from a garden center or nursery, be sure to do a thorough visual scan to check for indications of whiteflies before buying them and bringing them home. It is also important to keep the area around your garden or greenhouse tidy and free from unwanted weeds since such environments can be inviting to whiteflies. Planting marigolds around your tomato plants can also be helpful, as the flowers are believed to repel whiteflies as well as many other types of insect pests.
Natural Control Methods
For minor whitefly problems, yellow sticky traps can be very effective. For large scale infestations the introduction of predatory insects such as ladybugs, lacewings, predatory mites or Hymenoptera wasps can be invaluable. These beneficial insects may be available to purchase at your local plant nursery, though they can also be ordered online.