Thrips can enter greenhouses through migration, or via contaminated cuttings or seedlings.
Photo: Frank Peairs, Colorado State University, Bugwood.org

By the time spring rolls around, Baucom’s Nursery in North Carolina is often battling problematic thrips that come in through its greenhouses’ open vents. Between its two locations in Charlotte and Concord, N.C., the nursery has about 30 acres of undercover production space to defend, says head grower Jeff Watson.

In addition to shrubs, which make up 60 to 70 percent of Baucom’s business, the nursery also produces floriculture crops such as begonias, salvias, vinca and impatiens. Plus, Watson says, “We do a large amount of gerbera daisies, which are probably the most thrip-loving crop out there. We do several hundred thousand gerberas.”

Western flower thrips are the issue at Baucom’s. This is the predominant thrips species that affects greenhouse production, says Dr. Juang-Horng (J.C.) Chong, associate professor and extension specialist at Clemson University. Thrips come in most often through migration from the outside, as at Baucom’s, but they can also infest cuttings and seedlings. For growers who operate greenhouses in the northern part of the country, most thrips in the winter are shipped in through contaminated cuttings and seedlings.

Thrips feed by puncturing cells and sucking up the cell contents, Chong says. “They’ve got this modified mouthpart — what we call a rasping-sucking mouthpart — so they puncture the cell wall, and then suck up all the cell content inside,” he says. “When they remove all the cell content, only cell walls are left behind, resulting in stippling.”

Chong says thrips are particularly problematic on growing terminals such as flower buds and leaf buds because they permanently damage those terminals and prevent them from expanding normally.

Thrips prevention and identification

Chong’s experience with thrips is primarily in the southern U.S., where thrips generally come into greenhouses from the outside. “For growers in the south or anywhere with an open greenhouse kind of production, they would have to monitor with sticky cards,” he says.

Installing screens could help some growers who have thrips coming in from the outside. However, because thrips are so small, screens would have to be even smaller, Chong says. When screens are too small, they can impede airflow, raise humidity and allow for foliar disease issues.

If growers have cuttings or seedlings infested by thrips, they could perform a general quarantine, Chong says. “They would just take samples to see whether they have thrips on them,” he says. “They could either put sticky cards right among the cuttings themselves, or they can just sacrifice a few of their cuttings and take a look under a microscope or hand lens.”

Chong recommends any grower can benefit from using a hand lens to identify pest and disease issues, and this is something Baucom’s does. Each of Watson’s growers have loupe lenses. “As a matter of fact, [I] just bought some off Amazon that are jeweler’s magnifiers that have lights and everything with them.”

Plant damage caused by western flower thrips
Photo: Chazz Hesselein, Alabama Cooperative Extension System, Bugwood.org

Methods of controlling thrips

When thrips infest crops, they are hard to manage because they find their way into immature flower buds, Chong says. “If the bud is not opened yet and you apply something over the top of it, when the bud opens, the new tissue are not protected,” he says. “What you end up having to do is keep spraying, do repeated applications, so you can actually provide residual protection to all the newly expanded tissues.”

Through seminars and conversation, Watson has discovered one thrips-fighting trick that works for him: applying brown sugar to his crops. “It’s strange, but believe it or not, it does help draw out the thrips,” he says. He tank-mixes the sucrose-molasses product with insecticides such as Hachi-Hachi SC from SePRO.

Watson says he uses several SePRO products, including Hachi-Hachi SC, Rycar, Akari and Talus. “In the past few years, they’ve come up with some really good chemicals,” Watson says.

Hachi-Hachi SC, in the Insecticide Resistance Action Committee (IRAC) group 21A, stops the production of a chemical inside insects that provides energy to insects. “Probably the easiest way to understand it is, they just run out of juice,” he says.

In the case of chilli thrips, Rycar, in IRAC group 9B interferes with the pests’ nervous systems, Chong says. “One of the ways they feed is to suck up the juice from the plant cell,” he says. “Rycar actually interferes with that process, so they stop the action of the pumping motion, so they cannot suck anymore. In that sense, they basically starve to death.”

Growers should treat thrips whenever they find them, Chong says. “What I usually recommend is, make one or two applications, and then do another scouting or another sampling just to see if you still have a problem,” he says. “If you do, then you may need additional applications as well. As far as the time of the year — Florida, all year long; Canada, you probably are spared in the winter. But it probably is always a good idea to scout for thrips whenever you’ve got crops in a greenhouse.” — Patrick Williams

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