Pest Of The Month: Whitefly
According to John Palumbo, a professor and Extension specialist at the University of Arizona, in the Southwest and California, melons are its preferred host followed closely by Brassica crops. To a lesser extent, leafy vegetables also can become a target of the whitefly. Melons, in particular, have been impacted by adult populations because adults have the ability to vector Cucurbit Yellows Stunting Disorder Virus (CYSDV). Infected plants typically show yellowing and leaves roll upward, which can lead to economic loss. Whiteflies also vector geminivirus that can cause severe reduction in yields.
Life Cycle Of The Pest
Adults are usually present in fields soon after plants emerge, says Palumbo. Eggs are laid on the undersides of young leaves almost immediately, and nymphs hatch in three to four days. When a grower sees masses of adults on the undersides of terminal leaves, this is the first sign that he has a big problem, he adds.
“This would soon be followed by the presence of nymphs, and much later the presence of honeydew,” explains Palumbo. “At that point, you’re generally too late to prevent economic damage.”
Honeydew, the substance excreted by nymphs after they have removed plant juices, accumulates on the crops and serves as a medium for the growth of a black, sooty mold. “The honeydew and sooty mold contaminate the marketable portion of vegetable crops and essentially render them unmarketable,” says Palumbo.
Management And Control Strategies
Control as early in the season as possible is critical. With the increased insensitivity to products such as imidacloprid, Palumbo encourages growers to include cultural practices into their management programs that will reduce the numbers of whiteflies in their area.
“This would include careful attention to proper crop management and scheduling, and most importantly, sanitation practices including the timely destruction of harvested plant residue,” he says.
In addition, several products are available to growers that provide control of whiteflies. Palumbo says alternative neonicotinoids provide efficacy of both adults and nymphs either via systemic soil applications with products such as Venom (dinotefuran, Valent U.S.A. Corp.) Scorpion (dinotefuran, Gowan Co.), or Platinum (thiamethoxam, Syngenta Crop Protection); or through foliar application with translaminar activity with Venom, Assail (acetamiprid, United Phosphorus, Inc.), Scorpion, or Actara (thiamethoxam, Syngenta Crop Protection).
“When applied prior to plant emergence, either through drip chemigation, or as a soil, shank injection at planting, a systemic neonicotinoid insecticide is quickly taken up by the plant and distributed via the vascular tissue to the newly emerging plant growth,” he says. “As adults feed on this plant tissue, they are quickly killed before they are able to lay a large number of eggs.”
Management with a soil systemic insecticide also helps with controlling the vector of viruses such as CYSDV, explains Palumbo. This management strategy has been shown to reduce primary virus infection, and can suppress the subsequent spread of virus throughout the field.