Control Whiteflies Before They Control Your Crop

Tomato plant showing symptoms of Tomato Yellow Leaf Curl Virus

When it comes to whiteflies, it’s always better to control them before they become a problem. Because whiteflies carry a number of viruses harmful to tomatoes and cucurbits, starting early with a control program is important. Historically, whiteflies are not usually a concern in the spring in the Southeast, but because of mild winters in recent years, populations are building.

Shine Taylor, Ph.D., field development representative for DuPont Crop Protection, says he received calls about irregular ripening, a physiological disorder caused by immature whitefly nymphs feeding on tomatoes, early than ever this year.

“I was getting those calls even in December and January this year,” Taylor says. “Usually I don’t see those until about April. I would anticipate this being an issue in the rest of the Southeast this year, because we haven’t had the cold snaps we normally get. In southern Georgia in the middle of February and March, we were in the 80s.”

Taylor says he hasn’t seen a lot of Tomato Yellow Leaf Curl virus (TYLCV) early but pressure is climbing, the chief concern when it comes to whiteflies and tomatoes, this year, but that is spread by the adults.

“There seems to have been more lack of control of the immatures, so maybe the incidence of Tomato Yellow Leaf Curl virus is lower, but there’s still a lot of whiteflies out there,” Taylor says.

 

Get a Head Start at Planting

Taylor recommends applying a systemic insecticide such as Verimark (Cyazypyr™) through transplant water or as a tray drench at planting, especially if you have a field with a history of whitefly and TYLCV.

“With a good adult whitefly knockdown program, Verimark will give you 25 to 30 days of control,” he says. “Then you can come back with a neonicotinoid. It could be an old standard such as imidacloprid, or it could be one of the newer chemistries that have been launched. That should give you control for the next 30 days if you make the right application at the right time, and will get you to the second tie or further.

What Taylor recommends next depends on your crop. After fruit set, the worry about TYLCV lessens on determinate round or roma varieties, but control of the immature nymphs becomes important.

“The immatures cause irregular ripening, which damages the crop,” Taylor says. “There are a number of good chemistries to control immatures. You can come in with an [IRAC MoA] Group 28 such as Coragen® (Rynaxypyr®) five to seven weeks after the initial tray drench. That will control the immatures at a critical time. Our standard for whitefly control for the before Cyazypyr was a group 4 (neonicotinoid) at transplant followed by an application of Coragen (Rynaxypyr® ) at 5 and 7 weeks after transplant, but as new compounds and MoAs become available it gives the growers more options.” It depends on the pest pressure you have seen and if you have other pests that are even more important, such as leaf miners or worms. “The take home message is you want to put your most efficacious products at the most critical times depending on insect pressure and growth stages of the crop.”

Indeterminate tomatoes, such as grapes and cherries, have a longer season and may be in the ground for six months or more. Taylor says other products effective on the immature stage include insect growth regulators (IGRs) and chitin synthesis inhibitors, which offer completely different modes of action than mentioned above. They can be rotated into the program along with continued adult controls such as pyrethroids for a good insecticide resistance management (IRM) program.

 

Complements to Chemicals

Cultural practices are also important. In fact, they are especially important, Taylor says, because they impact the whole system.

“The genetics of the plant can make a big difference,” Taylor says. If tolerance or resistance to the TYLCV or other viruses are built into that plant, that helps tremendously. Simple things such as proper nutrition and water management not only help your yield, but help plants resist pests and diseases. Destroying old crops so we don’t perpetuate pest problems is also important.”

One low-tech idea that works well, Taylor says, is reflective mulch. The silver or aluminized plastic is disorienting to not just whiteflies, but other sucking pests as well.

“It looks like a mirror to them – they don’t know which way is up or down and can’t find the plants,” Taylor says. It works best early in the season, before the plants grow and cover up the plastic. We’ve done numerous tests that shows it really does impact the numbers of whiteflies, thrips, aphids and other sucking pests.”

 

Robin Siktberg is custom content editor for Meister Media Worldwide, publisher of American Vegetable Grower.