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Invasive bug threatens NM brassica crops

Brassica crops such as bok choy, cabbage and broccoli in New Mexico are in danger of attack from a new invasive pest – a stink bug called Bagrada hilaris. (Courtesy of NMSU)

Brassica crops such as bok choy, cabbage and broccoli in New Mexico are in danger of attack from a new invasive pest – a stink bug called Bagrada hilaris. (Courtesy of NMSU)

LOS LUNAS — Brassica crops in New Mexico are in danger of attack from a new invasive pest – a stink bug called Bagrada hilaris, which is currently spreading through the southern part of the United States.

Researchers from New Mexico State University have joined others from California and Arizona to determine ways to control this insect, which could devastate some of the niche-market crops raised by New Mexico’s small-scale and organic growers.

“The Bagrada bug was first found in New Mexico in 2010 in Las Cruces and has since migrated as far north as Santa Fe County,” said Tessa Grasswitz, NMSU Extension integrated pest management specialist and the U.S. Department of Agriculture’s state IPM coordinator. “This insect is native to southern Africa and has recently spread to parts of southern Europe and Asia, becoming a serious problem in India and elsewhere.”

It mainly attacks crops in the brassica family, which includes various Asian greens, such as bok choy, as well as mustard greens, cabbage, cauliflower and broccoli. Grasswitz’s research at the Agricultural Science Center at Los Lunas is among the first in the nation to address management tactics for this pest in organic growing systems.

“Until now, this has been a neglected area of research, because in California and Arizona, where the insect was first found, the main concern has been to protect large-scale conventionally grown brassica crops,” Grasswitz said.

“This insect has sucking mouth parts, which it uses to suck nutrients from the plant,” she said. “While feeding, it also injects a toxin that causes affected leaves to take on a scorched appearance, eventually turning brown and dying.

In the main vegetable-growing areas of California and Arizona, growers struggle with establishment of their plants because the pest can kill the emerging seedlings.

“Some of these commercial growers have been spraying with various conventional insecticides every three days for three weeks during the establishment phase of the crop to get a stand,” she said. “For organic growers, it’s much more problematic, because organic insecticides are not as potent as conventional products. So dealing with Bagrada bug is a real issue for organic producers.”

Grasswitz is trying to develop integrated pest management strategies for organic growers to use against the Bagrada bug. These tactics include determining the insect’s host plant preferences in order to develop a trap-cropping system, assessing the impact of native predators and parasites and testing various organic insecticides.

“One of our first tasks was to find the insect’s preferred host plant to use as a trap-crop,” she said of her research that began in 2012. “We found that Bagrada bugs are strongly attracted to spring raab, so we used this plant as a basis for a trap-cropping experiment in 2013, with arugula as the main crop.”

In an IPM program, a trap-crop of the preferred host is planted to attract the pest away from the main crop. Once the insect is attracted to the trap-crop, controls are applied to eliminate the bug.

“The trap-crop proved highly attractive to adult Bagrada bugs,” Grasswitz said of the 2013 research. “But the system as a whole failed because we were unable to control the pest with currently available organic insecticides before it started to reproduce.”

However, Grasswitz conducted an additional late-season insecticide trial in October that was more successful.

“The better control may have been due to the slower breakdown of active ingredients under the less-intense sunlight at that time,” she said. “Trap-cropping may still be useful in protecting fall brassica plantings in organic systems, or for mid-season production of conventionally grown crops.”

For the time being, while Grasswitz continues to look for better ways to manage the bugs, she is advising growers of brassica crops to use a physical method of control.

“For small-scale and organic growers, if the pest is established in their region, the best thing they can do to protect the crop, at least initially, is to use floating row covers, which can be very effective” she said. “We are also trying to work out some strategic planting dates for brassica crops in different parts of the state so that growers can avoid peak Bagrada populations.”

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