Aug 20, 2015

Bagrada bug, BMSB starting to harass Western growers

Two invasive bugs have been causing a stink among many Western fruit and vegetable growers, with each pest targeting a slightly different set of crops. As the bagrada bug and brown marmorated stink bug (BMSB) expand their reach, they challenge growers and researchers to develop new crop protection programs.

Bagrada bug

Bagrada bugs prefer members of the brassica family, including broccoli, cabbage and cauliflower. A member of the stink bug family, the 3/16- to 1/4-inch black and red insect damages plants when it inserts a needle-like feeding proboscis into tissue and sucks out the sap.

Both adults and immature nymphs target newly emerged seedlings or newly planted transplants, feeding on cotyledons, new leaves and growing points. This can cause wilting, stunting and even death.

If the growing point is killed, the plant may yield no heads or may compensate by producing multiple branches that yield unmarketable heads.

Since the bagrada bug was first confirmed in Los Angeles County in 2008, it has spread throughout much of the southwestern cool-season vegetable production area, including California’s desert and coastal regions, Arizona, Nevada, New Mexico, Mexico and more recently, Texas.

“We’ve found it everywhere,” said Raul Villanueva, Texas AgriLife Extension entomologist based in Weslaco. “Initially we found it in a field of sorghum, but when we started monitoring cabbage and broccoli fields, we found it there.”

The discoveries came in May, after most of the crops in Texas’ Rio Grande Valley had been harvested. But Villanueva will be working to educate growers about treatment programs before they begin to plant cabbage and other brassicas in October and November.

The bagrada bug is not a strong flier and moves mostly by hitchhiking. With Texas now the largest port of entry for Mexican produce imports, Villanueva said the pest has the potential to spread rapidly.

“I think it’s going to be easy to move it to the eastern United States,” he said.

As with most new pests, it typically takes about two years for growers to develop an effective management program, and the bagrada bug has been no exception, said John Palumbo, a University of Arizona entomologist based in Yuma.

“I think most of the (desert) guys are on top of it now,” he said. “You have to be extremely aggressive from the cotyledon to the two- to three-leaf stage, then watch it to the six- to seven-leaf stage.”

The program starts as soon as transplants are in the ground or seedlings have germinated ­beginning in early September , with growers chemigating a pesticide through overhead sprinklers.

Typically, they’ll continue to treat on about a five-day schedule until the plants reach the six- to seven-leaf stage, when they’re no longer susceptible to substantial damage.

Since the bagrada bug has moved into the desert, Palumbo said growers of winter cole crops have doubled the number of insecticide sprays they apply during the season.

BMSB

Brown marmorated stink bugs were first confirmed in Allentown, Pennsylvania, in the late 1990s. By 2010, they were entrenched throughout much of the East and caused $37 million in damage to the Eastern apple crop that year, according to figures from the U.S. Apple Association. They’ve continued to expand their range and have been trapped in most states.

BMSB has a wide host range spanning more than 200 different plant species, including numerous crops of agronomic importance.

The pest showed up in Portland, Oregon, in 2004, and has migrated from urban areas to begin causing scattered damage to fruit and hazelnut crops in the Willamette Valley in 2014, said Vaughn Walton, a horticultural entomologist at Oregon State University in Corvallis. Growers will know this fall whether the trend continues.

“That’s the time when growers will start to have fruit coming to the wineries or they will have nuts to the processors, and that’s when they will start to see stink bug, but the damage can actually start happening this time of year,” he said in mid-July. “The numbers here in Oregon are decidedly increasing year over year if we’re looking at the same location.”

A rather nondescript brown, BMSB is about the same size as other common stink bugs. It feeds by inserting a straw-like stylet into fruits or vegetables to suck out plant juices. During feeding, it injects plant toxins that cause corky lesions around the feeding site and render produce unmarketable.

In hazelnuts, early season feeding can damage the developing kernels, causing them to shrivel and leaving blank nuts. Feeding later in the season causes corky lesions.

In two commercial hazelnut orchards, Walters said feeding – presumably by BMSB – was high enough last season to cause shrivel in 5 percent of the nuts.

Until recently, the filbertworm was considered the industry’s top pest, and 1 percent damage was considered acceptable, he said.

Doug Olsen, a Newberg-area hazelnut grower and president of the Hazelnut Grower Bargaining Association, owned one of the damaged orchards. This season, he’s cooperating with Oregon State University on trapping and a caged nymph study.

“It’s a growing concern, but in softer fruits like apples and pears I think it’s a bigger concern,” Olsen said of BMSB.

That’s because pome fruit is picked in the fall, the same time the bugs begin to aggregate for the winter, Walters said.

Based on reports from the East, he theorized Pacific Northwestern berry growers may not see as much damage because treatments that target spotted wing drosophila also help suppress BMSB.

Winegrapes don’t appear to be a preferred food, Walton said. Instead, the bugs congregate on grape clusters in the fall. When the fruit, along with the insects, is crushed at wineries, the pests can impart a cilantro off-flavor, ­or taint, ­if numbers are high enough.

University of California entomologists Frank Zalom and Kent Daane plan to conduct a survey of California’s vineyards this fall to determine whether BMSB has spread from urban areas.

So far, BMSB has confirmed breeding populations in the Los Angeles area as well as in Sacramento, Yuba City, Chico and Modesto, but has yet to be found in agricultural fields or orchards, Zalom said.

– Vicky Boyd