Even County Extension Agents get caught off guard. I rarely pay much attention to my gardenia. But the other day I noticed the leaves looked smutty. Under closer inspection I discovered whiteflies. They are like aphids in that they suck the sap of ornamentals. Leaving a honeydew that causes a mildewy stuff to grow on the upper side of the leaves. My boxwoods also are infested. So now I have to start treatment. Wish me luck.
Control:
whitefly control is difficult because the eggs and larvae have become resistant to many insecticides. Insect growth regulators such as kinoprene, azadiractin, diflubenzuron, pyriproxyfen and fenoxycarb should be used to aid in control of the immature stages. The other listed insecticides should be used to target both immatures and adults. Use both insect growth regulators and conventional insecticides for best control. Start chemical control early before populations build, using alternate sprays of insect growth regulators, insecticidal soap and horticultural oil. If adult populations are increasing, use one of the other insecticides to reduce the adult whitefly population.
Outdoors use: bifenthrin (Talstar Lawn and Tree 7.9 F), fluvalinate (Mavrik Aquaflow 22.3 F), endosulfan (Thiodan 50 WP, Thiodan 3 EC), acephate (Orthene Turf, Tree and Ornamental Spray 75 SP, Address T/O 75 SP), cyfluthrin (Advanced Garden Lawn and Garden Multi-
Insect Killer, Tempo 20 WP, outdoor use of Decathlon 20 WP designated for nurseries), beta-cyfluthrin (Tempo SC Ultra 1 SC), permethrin (Astro 36.8 EC), insecticidal soap (Safer Insecticidal Soap, M-Pede), horticultural oil (SunSpray Ultra-Fine Oil), pyrethrins plus piperonyl butoxide (Pyrenone), imidacloprid (Merit 75 WP, Merit 2 F, Marathon 60 WP, Advanced Garden Tree and Shrub Insect Control, Marathon II 2F), imidacloprid plus cyfluthrin (Advanced Garden Rose and Flower Insect Killer), disulfoton plus 12-18-6 fertilizer (Advanced Garden 2-in-1 systemic Rose and Flower Care), abamectin (Avid 0.15 EC), or azadirachtin (Azatin XL, Safer Bioneem, Ornazin 3% EC).
Follow label directions carefully. Repeat sprays every four to five days until whiteflies are under control. Do not use horticultural oil more than once per week.
