Thrips bugging regional growers
COLLEGE PARK, Md. — Several regional farmers found themselves contending with thrips in greenhouses and high tunnels over the last several weeks, the University of Maryland Extension said.
The tiny, yellowish-orange insects, which can scar crops and transmit tomato spotted wilt virus, pester all kinds of produce and typically spread due to poor sanitation, said Emily Zobel, a senior agent associate with the Extension.
“You can get thrip outbreaks in any kind of greenhouse or high tunnel,” she said. “They’ll kind of outbreak on anything.”
The insects feed by puncturing and consuming the content of a plant’s cells, leading to damage, including stippling or discolored flecking. Females lay their eggs into the plant tissue, and the insects have several generations — up to eight per year. In warm weather, the life cycle can be about two weeks.
Many operations have thrips at one time or another, but those that develop large infestations typically struggle with sanitation issues such as weeding, the Extension said. Weeds such as prickly lettuce, chickweed, spiny amaranth, lambsquarters, black nightshade and shepherd’s purse provide a refuge for the insects and a place to overwinter. Weeds can also host tomato spotted wilt virus, which attacks crops such as tobacco and tomatoes and can ruin their fresh-market salability, Zobel said.
Farms with thrips also grew bedding plants with vegetable transplants in the same greenhouse — a big no-no, the Extension said. Bedding plants are notorious for harboring thrips.
It may take between two and four weeks once thrips take hold of a plant for symptoms to show. Operations reported to the Extension showed up to a third of their plants with symptoms of the wilt virus infection. Growers can monitor for thrips with sticky cards placed at the height of the vegetable plant and checked two to three times a week. If they’re detected early, farmers may be able to use horticultural oils or biological controls, such as predatory mites, instead of pesticides.
Overhead irrigation can also be useful.
“If you have it, sometimes the water’s enough to knock them off the plants, and they’re so small they can have trouble getting back on,” Zobel said.
But if only a small number of plants are infected, a farmer can avoid more larger measures.
“It’s easier sometimes to remove a handful of plants than to apply insecticide to all of your plants,” she said. “The key to really controlling or preventing this is to take the time to do good sanitation.”