As growers get ready to transition to the desert for winter vegetable production, whiteflies are topping the list of the most notorious entomological thugs likely to wreak havoc on this year’s crop.

It’s not just a matter of whiteflies chomping on the plant — the problem is much more insidious due to the potential for disease vectoring.

“Our biggest concern at the moment is whether a new whitefly-transmitted virus, cucurbit yellows stunt disorder virus (CYSDV), will be a problem on our fall melon crop,” says John Palumbo, research entomologist with the University of Arizona.

“It was widespread last fall and caused significant economic losses in some cantaloupe and watermelon fields. We found on a number of melon fields in the Yuma area late in the spring growing season. So, we know the virus is present, and if it is going to be a problem again we should start to see symptoms in about 3-4 weeks.”

While whiteflies were once considered fairly limited in terms of mobility, research by other entomologists at the University of Arizona has largely debunked that theory.

“We know from marked release studies that, in the field, whiteflies can travel up to seven miles in a four-hour,” says David Byrne, UA entomology professor. “In addition, we recently found that they will fly more than just a day, so we can multiply that factor by another number. They’re also flying higher than we originally thought — we’ve captured viable whiteflies as high as 1,000 meters (3,280 feet).”

The tapestry of crop destruction woven by the whitefly in the desert southwest over the years is ever-changing.

“In 1979-1980, we had strain ‘A’,” Byrne says. “Then it was strain ‘B,’ which was even more competitive. Now, we’re looking at biotype ‘Q’.”

There’s an even bigger problem with “Q,” a strain originating in Europe, which has already shown signs of resistance to many materials commonly used for whitefly control with active ingredients pyriproxifen, imidacloprid, and acetamiprid.

“The ‘Q’ strain first showed up in Spain and has become very problematic,” Byrne says. “They can’t kill it now even if they throw a gallon jug at it. So far, it has mostly been detected only in greenhouse operations in the U.S. — particularly on poinsettias — but it is a huge concern for all of agriculture.”

Growers aren’t headed for the mat just yet, but they’re keeping a wary eye on the enemy.