The Bagrada bug mirrors an unpopular in-law that keeps coming back to visit.
The California and Arizona cole crop industries are all abuzz about the repeat appearance of the Bagrada bug, Bagrada hilaris, in low desert fields this fall in Southern California and Arizona.
The initial Bagrada bug outbreak in 2009 startled the desert cole crop industry when high insect numbers infested cole crop fields; targeting the plant’s growing point. The pest was first found in the United States in 2008 in Los Angeles County and then spread to neighboring Orange County.
“It’s early in the cole crop season, but I’d estimate the number of Bagrada bugs in Imperial County is about double the number I found last year,” said Rick Klicka, pest control adviser and owner of Southwest Ag Service, Brawley, Calif.
Klicka counted eight adult Bagrada bugs on the four true leaf, organically-grown Brussels sprout plant he examined in late September.
“I’ve seen dead plants caused by the Bagrada bug,” Klicka said. “Direct-seeded cole crops have the worst damage.”
The Bagrada bug is an equal opportunity pest, attacking conventionally- and organically-grown cole crops.
Adult and nymph Bagrada bugs suck sap from young cole crop leaves. The feeding results in small puncture marks visible as white patches on leaf edges. A heavily attacked plant has a scorched appearance. The end results can include plant death, plants without heads, or double or more heads too small for sale on the commercial market.
The Bagrada bug is a member of the Pentatomidae stink bug family; smaller in size than the average stink bug. The female Bagrada bug is larger than the male. September and October are the ideal period for insect development when temperatures average around 86 degrees.
The host range includes all cruciferous crops. Cole crops are in the Brassicaceae family including cabbage, cauliflower and broccoli, kale, kohlrabi and Brussels sprouts.
“With these Bagrada bug numbers, the PCA needs to be in the field once or twice a day to evaluate the bug infestation and determine the best treatment,” Klicka said. “I feel like I’ve been though half a season and actually we just got started.”
Other plant hosts include cotton and alfalfa, but plant damage has not been reported. Adult Bagrada bugs are 5-7 millimeters long with black, shield-shaped bodies with distinctive white and orange markings.
Bagrada bug numbers were lower in Yuma County early this season compared to the Imperial and Coachella valleys, says John Palumbo, but later became severe.
Palumbo is a University of Arizona Cooperative Extension research scientist and Extension specialist based at the Yuma Agricultural Center (YAC) in Yuma, Ariz.
“We have the Bagrada bug in cole crops and growers and PCAs are battling them,” Palumbo said. “At the YAC farm, we’ve had heavy numbers in broccoli seedling stands. We are getting lots of calls from the industry. All people want to talk about is the Bagrada bug and how to stop it.”
Insecticides including pyrethroids effectively control the Bagrada bug. The most common question growers and PCAs ask Palumbo is when sprays for the insect can be stopped.
“I really don’t know the answer to that question,” Palumbo acknowledged.
The plant’s susceptibility to feeding damage can vary on the specie of crop. Cabbage may be the most susceptible cole crop since it forms a head.
“The Bagrada bug can be killed with insecticides, but we really don’t know how many sprays are needed to protect the plant,” Palumbo said. “We can’t keep spraying all season long; it’s too expensive and resistance is always a concern.”
The Bagrada bug has five nymphal instar stages. First instar insects have reddish-brown heads and thoraxes plus bright-red abdomens. Later instars turn black. Eggs are oval and creamy white and turn orange with age.
The Bagrada bug is found in eastern and southern Africa, Egypt, Senegal and Zaire.
This season’s Bagrada bug outbreak proves the pesky insect can survive the winter in the low desert. Palumbo says cool and wet conditions prevalent this spring increased vegetative growth which probably led to higher insect populations.
Palumbo witnessed the insect in Imperial Valley and Yuma area citrus groves in July.
Bagrada bug control
For Bagrada bug control, Palumbo suggests pyrethroids in chemigation for a cost effective, quick knockdown, but foliar applications are the most effective. For aerial applications on larger plants, products including neonicotinoids and Lorsban offer good control.
“There is a lot to learn about the Bagrada bug,” Palumbo said. “It’s a brand new pest and it may take several years for us to figure out how to best manage the insect.”
Palumbo expects the pest to be less of a concern by November when temperatures cool off.
Eric Natwick, entomology farm advisor, University of California Cooperative Extension, Imperial County, Holtville, concurred that Bagrada bug numbers about doubled this fall in the county compared to last year.
“We’re finding high concentrations of the Bagrada bug,” Natwick said. “Even though we can spray and can kill the insect, large numbers are found again several days later.”
He found Bagrada bugs during the spring and summer months in canola, alfalfa, and cotton.
“We know it survives through the summer on weeds and some crop hosts even though it doesn’t necessarily cause damage to the plants,” Natwick said.
Cole crop nurserymen in September reported Bagrada bugs inside greenhouses.
“They treated them and then several days later had more Bagrada bugs in the greenhouse,” Natwick said. “I suggested soil treatments under the benches where the transplants are grown.”
Finding high Bagrada bug numbers this fall means the insect survived the spring and summer and more.
“We are generating our own Bagrada bugs now where last year we thought they came into the valley from the mountain areas to the west,” Natwick said.
Stink bugs are more active at night due to cooler temperatures. During the day the insects stay mostly in the soil or in dirt clod shadows to escape the heat.
Growing cole crops under row covers is an option to protect plants from the Bagrada bug, but is an expensive option, Natwick says.