Small, white smears appear on automobile windshields throughout south Georgia now. They're signs of head-on collisions with whiteflies. The minuscule menaces are hitting vegetable farmers hard, too, says a University of Georgia entomologist.
Whiteflies are a sixteenth of an inch long and are white. They suck the juice from plant leaves to survive, said Alton "Stormy" Sparks, a vegetable entomologist with the UGA College of Agricultural and Environmental Sciences in Tifton, Ga.
They prefer vegetables such as squash, tomatoes, cucumbers and greens. But they'll hit cotton and many landscape plants.
The flies are typically a problem at this time every year as they begin to show up in mass around Georgia's vegetable production region, Sparks said. In some places, hordes of them fall from the sky like tiny snowflakes. But they've been exceptionally bad this year for two reasons: heat and drought.
"They thrive in hot, dry conditions," he said, "and do better on drought-stressed plants."
In Georgia's recent weather, hungry whiteflies can take over a field in a hurry, he said. A female whitefly can easily produce 300 or more offspring. In seven to 10 days, the females from that hatch can produce another 300 or more.
Based on this and anecdotal reports from UGA Cooperative Extension agents in vegetable-growing counties, he said, some places may be seeing record numbers of whiteflies.
For example, there have been reports of at least 500 whiteflies on every leaf on some plants in and around Tift County, he said. Research shows that farmers need to spray pesticides to control whiteflies in squash when five or more appear on each plant leaf.
"If you have that kind of whitefly population coupled with any disease pressure," he said, "entire fields could be wiped out."
Vegetable farmers are trying to control them, he said. But they're losing.
During a normal summer, farmers spend $60 per acre to control whiteflies to make the best yields in vegetables. This year, farmers will spend three times that and still get reduced yields, he said. Squash yields alone will be slashed as much as 50 percent.
The flies trouble south Georgia, but they could move north, Sparks said. A strong breeze can blow them several hundred miles.
"But to become a problem like they are here, there would need to be suitable host plants currently growing in regions north of here," he said.
Good, hard rain will knock whitefly populations down, he said. But if hot, dry conditions follow, they can rebound quickly.
"There's a good chance whiteflies will become more of a problem as we continue into late summer," he said, "especially if we continue to have the weather we've been having."
Sparks and other CAES scientists are testing new pesticides, not yet available to farmers, to control whiteflies in the future.
Whiteflies hit home landscapes hard at this time of year, too. If plants aren't growing as well as expected and a slight brush of a leaf produces a flurry of white bugs, almost like a puff of smoke, whiteflies are likely to blame.
Local UGA Extension agents (1-800-ASK-UGA1) know what you can do to control them.