Inspect citrus trees for whiteflies throughout the spring and summer, paying close attention to leaves just above areas coated with honeydew or sooty mold. Prune off and discard severely infested leaves, dipping your sheers or loppers into a solution containing 9 parts water and 1 part chlorine bleach between each cut. Sanitizing your pruning tools helps prevent spreading the tiny pests and any plant diseases to other parts of your tree.
Spraying the citrus tree's leaves with a strong blast of water from a garden hose rinses feeding whiteflies away. Texas Cooperative Extension recommends spraying the tree at least once weekly for three weeks. Sucking whiteflies off the lower leaves with a small, handheld vacuum can control localized whitefly populations, but do so in the early morning when the low temperatures make the pests sluggish. Place the vacuum bag inside a zip-top plastic bag and freeze it for about 24 hours to kill the whiteflies, then throw the dead insects into a covered trash can.
Hanging yellow sticky traps can help reduce the number of whiteflies flitting around your citrus trees. You can buy traps, or make your own using pieces of 12- by 6-inch plywood or cardboard painted bright yellow and coated with a homemade adhesive containing equal amounts of petroleum jelly and household detergent. Mount the traps on wooden stakes and drive them into the soil surrounding the infested tree. Check the traps at least once a week and clean or replace them when they're no longer sticky.
Spraying infested citrus trees with insecticidal soap can help control whiteflies. Carefully read and follow the mixing instructions and safety precautions on the manufacturer's label. One product recommends mixing 5 to 8 tablespoons of insecticidal soap concentrate for every 1 gallon of water. Use a small garden sprayer to thoroughly coat the foliage, taking care to completely cover the undersides of leaves where the pests gather to feed. Repeat treatments every four to seven days until you spot no more whiteflies flitting around the tree.
Spray the trees on calm days when no rain is expected for at least 24 hours. Avoid treating citrus trees when the temperature rises above 80 degrees Fahrenheit or you risk damaging the foliage. Although nontoxic to people or animals, insecticidal soap can still cause eye and skin irritation. Wear waterproof gloves, shoes with socks, long sleeves, pants, goggles and a face mask to reduce your risk of exposure. Keep kids and pets out of the treatment area until the soap solution dries completely.
Welcome Beneficial Insects
Whiteflies have many natural predators, including ladybugs, lacewings and spiders. Those beneficial critters can help control whiteflies unless they're killed off by broad-spectrum insecticides, ants or dust. Using insecticidal soap solutions instead of stronger pesticides helps keep the predators alive and feeding on whiteflies. Periodically rinse the dust from the leaves with a blast of water from a garden hose so the beneficial insects can easily reach the pests. If sugar-feeding ants are protecting the whiteflies, place a sugar water bait beneath the tree's canopy or coat a strip of fabric with a sticky substance containing polybutene and wrap the fabric around the tree's trunk.