Best Pest Managments against (PFB) and (BMSB)

(originally published June 2018)

 

Hazelnut acres are surging in Oregon despite the challenges being raised by two significant insect pests.

The opportunistic Pacific flathead borer (PFB) preys on newly planted hazelnut trees while the invasive brown marmorated stinkbug (BMSB) continues to infest orchards and destroy nut crops.

BMSB

The brown marmorated stinkbug, a native of Asia, was introduced on the east coast in the 1990s and by 2004 was detected in Oregon. Nik Wiman, Oregon State University (OSU) orchard specialist, said BMSB damage to hazelnut crops was confirmed in 2012.

This pest has also been found in California, but mostly in urban areas. There has been speculation by researchers that the prolonged high summer temperatures in California may be a limiting factor with this pest. Oregon, with forested areas adjacent to many orchard crops, may have a bigger challenge with this tree-loving pest.

Adult BMSB has a typical stinkbug shape, white bands on its antennae and legs, rounded shoulders and a prominent light-dark banding pattern on its abdomen. BMSB eggs are barrel shaped, white to pale green in color and can be found as masses on leaves. Newly hatched nymphs are difficult to distinguish from native stinkbug nymphs.

BMSBs produce one generation per year, although two generations have been documented in California. After mating in the spring, the female BMSB lays eggs in clusters on plant material. In the fall, mature BMSB will aggregate and move to protected places, including structures, to over winter.

BMSB Damage

Wiman said BMSB feeds on all parts of the plant and hazelnut trees can be a single host. Economic damage comes from BMSB feeding on hazelnut kernels through the shell late in the season. Feeding can also introduce pathogens. The damage may go unnoticed at harvest, but nut sampling by processors may find damage.

BMSB feeding may go undetected as the damage to the nuts resembles other causes.

“There’s no good handle on this,” Wiman noted. There is ongoing research in BMSB early feeding habits causes for shriveled or aborted nuts.

BMSB Control Options

Growers who find high numbers of adult BMSB feeding have few choices in control. Pyrethroid products are effective, Wiman said, but studies have shown that complete coverage of an orchard may have harmful effects on beneficial insects and may cause flare-ups in populations of mites or aphids.

Spraying borders, or alternating rows in an orchard can be effective BMSB control, Wiman said. Timing can also help, as nymphs are easier to kill than adults.

Wiman said that long term, the best bet for BMSB control will be natural enemies. The wasp, Trissolcus japonicus, also known as the “samurai wasp,” appears to be the best bet for biological control of BMSB, according to Wiman. The wasp originates from the same areas of Asia as BMSB. A parasitoid, it hunts for the egg masses laid by adult BMSB and lays eggs in each of the eggs. The parasitic wasps develops inside the eggs and chew their way out after hatching, destroying the BMSB eggs. Wiman said he believes establishment of the wasp in Oregon hazelnut production regions will be the long-term solution to BMSB control.

BMSB Emergence

BMSB adults began emerging from overwintering sites in April. OSU researchers reported capturing the first BMSB of the season in baited traps in the Willamette Valley. They are working to develop trap catch thresholds to determine if spray applications are necessary. They will also be monitoring orchards for samurai wasp activity.

PFB

Newly planted hazelnut acreage became the target of the Pacific flatheaded borer several years ago. Damage by this destructive beetle came to light two years ago as acreage was expanding.

Wiman said PFB is not a threat to mature trees, but it will kill young trees. Populations of this pest are higher in foothill regions and orchards planted adjacent to forested areas seem to have more PFB infestations. Drought and water stress are also linked to PFB infestations.

Adult PFB are a quarter to nearly a half-inch in length, and are bronze or metallic in color. They are destructive in the larval stage. Female PFB lay their eggs in weak points of the tree. Sunburn, pruning wounds or cracks in the bark leave openings for egg laying.

These pests tend to attack weak, new trees that are showing signs of stress from drought or over watering or plantings in marginal soils, Wiman said.

PFB Damage

Chemical control of PFB is difficult as they are protected by the tree bark. Pesticide applications can prevent additional infestations, but do nothing to the destructive larvae that are already burrowing into the wood. 

Larvae may feed in one area or travel to feed on the cambium layer and zylem. Their mines through the wood can resemble a spiral pattern as they girdle the tree. Frass or sawdust may be visible on the ground below the entrance hole where PFB larvae are feeding.

Tunnels through the wood are packed with sawdust and the tunnels will be wider than they are tall. Spongy wood can be a symptom of active PFB larvae feeding. Trees that have been partially or completely girdled due to feeding generally die. Cankers form at feeding sites and block nutrient and water delivery from roots to leaves and branches. Borer-infested trees appear wilted, have yellow leaves and do not respond to irrigation water application.

PFB damage will be visible late in the growing season. Inspection for damage should start at the soil line and move up about three feet. PFB may overwinter in the center of the tree. In spring, PFB larvae will pupate and then emerge as adults in early summer.

Controlling Tree Stress

Wiman said that stress to young trees can increase chances of PFB infestation. Healthy nursery trees should be planted early in the dormant season to give them an opportunity to establish a good root system before the onset of high summer temperatures.

Sunburn on tree trunks is a major factor in PFB attacks and Wiman noted that painting the trunks with a 70 percent dilution of white latex paint offers some protection from sunburn. Trunk guards can also protect young trees from sunburn and herbicide damage but do not protect against PFB as the trees are attacked above the guard and larvae mine downward inside the guard. The guards also make it difficult to spot PFB infestations.

Wiman said it is also important to remove infested trees, as they are a source of new generations of PFB. Cut or diseased trees should be removed from the orchard.