Bagrada bug spreads, threatening winter vegetables
As you inspect your garden following winter rains, look for an odd, shield-shaped bug, about one-fifth of an inch long, black with white and orange markings. This is the adult Bagrada bug, which goes after winter crops such as cabbage, kale, broccoli, arugula, cauliflower and radish. It sucks the sap out of tender leaves, leaving puncture marks and a stippled or wilted leaf. The pest can stunt growth or kill plants.
The bug will also go after warm-weather crops such as papaya, potato, corn and beans, but is more lethargic in heat. It spends its time in the soil, laying eggs or hiding; heavy rains drive it out of air pockets and onto the plant du jour.
The Bagrada bug is a global pest, particularly in southern Europe, southeast Asia and northern Africa, where it may have originated. It turned up in Los Angeles County a few years ago, first spotted by a gardener who thought she had a cluster of ladybugs inhabiting her alyssum. In one of its younger nymph stages, the Bagrada is round and resembles a brightly colored ladybug.
So the bug is good at disguise. It also has a potent aroma. "Once you smell it, you will never forget it," said Gevork Arakelian, senior biologist at the Los Angeles County Department of Agricultural Commissioner/Weights and Measures. "It's very specific for stinkbugs, a pungent, intense, parsley odor. Birds don't touch them. If they eat one, they disgorge it immediately."
Unlike the harlequin bug, which it strongly resembles, the Bagrada bug lays most of its eggs in the soil, so natural predators such as wasps aren't effective controls. Picking the bugs off plants by hand is not feasible because the infestations are so thick and sudden, with multiple generations occupying one plant at a time.
"Maybe you could do it with a vacuum cleaner," Arakelian said, almost joking. "This is a very bad pest and organics won't be strong enough to control this."
He recently heard about a grower laying down enough fine mesh to cover 100 acres of cabbages and turnips, specifically to stop the bug. A home gardener could do the same, he said, by burying the mesh around the garden. "The mesh has to be fine enough that the nymphs can't get through," he said.
Insecticides aren't an option for many, he said. Adult bugs will simply flee one garden for another, only to return when the residue of pesticide is gone.
The bugs have turned up on beaches in north San Diego County, where they were thought to be attacking nearby succulents. Arakelian was just up in the Ventura County foothills and saw the Bagrada bug.
"I was almost on top of a mountain and these things were all over the wild mustard," he said. "They have spread all over Southern California."
You can get more information and photos on this UC Riverside PDF and Arakelian's pest sheets.
-- Jeff Spurrier
Photo credits: Gevork Arakelian