Filbertworm eggs in the orchard

Orchards in the Willamette Valley have now received enough heat units to have filbertworm eggs (>815 degree-days since April 1) and most have now achieved first egg hatch (955 degree-days). Some orchards will already have a few larvae entering nuts (1022 degree-days). You should have first cover sprays on by now if you are treating based on moth captures in pheromone traps or a history of pressure. We put out our trial on Monday just ahead of egg hatch for our location.

Note that moth counts have yet to peak and by the time they do peak at 1188 degree-days, nut infestation has already occurred from the reproductive efforts of the first moths that emerged. Many of us have concerns about the phenology model for filbertworm (developed in 1983 by M.T. AliNiazee) and its performance in our more variable climate these days.

This week OSU graduate student Erica Rudolph was out looking for signs of eggs that the model predicted should be out there. On Tuesday the 19th she found a fresh filbertworm egg. This is not an easy task as the eggs are laid singly on leaves or clusters and they are very small. She is examining a lot of plant material.

Today, July 22, Erica found two more eggs. One is intermediate in development and has darkened compared to the fresh egg. Some traces of the developing gut of the larvae are apparent. On the second egg found today, the black head capsule of the first instar larva is fully formed and showing, indicating that it is just about finished with embryonic development and is about to hatch! So far so good for model predictions.

A very fresh filbertworm egg has a shiny chorion (shell) and creamy interior. Photo: Erica Rudolph
A developing filbertworm egg. Photo: Erica Rudolph

Fully developed filbertworm egg with neonate larva ready to hatch. Photo: Erica Rudolph

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BMSB egg masses and nymphs now in orchards

BMSB egg mass on young ‘Jefferson’ tree near Aurora, OR. Photo: Kody Transue
EM9164 from the OSU Extension catalog describing how to determine if BMSB egg masses are parasitized by Trissolcus japonicus.
BMSB 2nd instar on nuts. These small nymphs are not damaging but as they mature they are increasingly able to penetrate the kernel. Photo: NIk Wiman

Brown marmorated stink bug (BMSB, Halyomorpha halys) is a direct pest of hazelnuts across its invaded range worldwide including in the Pacific Northwest. Our program began redistribution efforts of the biological control agent Trissolcus japonicus soon after it was discovered attacking egg masses of BMSB in Portland in 2015. Since our initial efforts, the ODA has begun ramping up the wasp releases and they are putting out some impressive numbers. Our sampling is showing that at many sites evidence of the wasp can be found year after year, suggesting it is well-established in some but not all areas of the Willamette Valley and more broadly across Oregon.

The very first BMSB egg mass that I found this season was parasitized by the wasp – a very good sign. We have a lot of information about this wasp posted and we continue to encourage reporting of parasitized egg masses. There is little doubt that successful biological control of BMSB is the best option for management for this pest that is found across the landscape.

Regardless of the improving levels of biological control, this insect remains a threat to the hazelnut industry. It is likely that we will continue to experience kernel damage from this pest into the future, though it seems the populations are highly variable year to year. Last year (2021 growing season) the BMSB populations were low and processors reported minimal damage. However, in the previous year (2020), there was considerable damage. The environment has a lot to do with these population fluctuations. This pest is also highly variable spatially. Many orchards get no pressure.

We have been trapping adults all spring and I have seen adults in the orchard on several occasions. Last week I saw second instar nymphs in the orchard on nut clusters. This Monday the 18 of July we encountered an egg mass that had just hatched in an orchard where we have a filbertworm trial.

Previous work has shown that hazelnut damage increases at the time the nymph population increases. So it is a good time to scout for BMSB. We hope to further refine trap captures help growers determine if management is necessary.

BMSB management info is found in EM8328, the Hazelnut Pest Management Guide.

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Brown, aborted nuts linked to Pseudomonas infection

Hazelnut growers around the world are familiar with the bacterial pathogen Xanthomonas arboricola pv. corylina, which is the cause of bacterial blight. Historically, no other bacterial pathogens have been problematic in Oregon hazelnuts. However, this season I became concerned with a high frequency of nut clusters with brown, aborted nuts, particularly in ‘Yamhill’. I know I have seen this in past years, but it seems to be fairly prominent this season. Could it be the increased rainfall this spring? When I submitted some of these nuts at the OSU Plant Clinic, pure cultures of Pseudomonas syringae were isolated from them. The pathovar remains unknown at this time pending genetic characterization.

In Europe, for years they have had problems with P. syringae pv. avellana in hazelnut, which causes necrotic buds, rapid whithering of leaves on branches, brown cambium, pale foliage, and tree death.

Photos of symptomatic nuts are pictured at right, note that the husk was brown and black necrotic tissue was found on the basal scar. Subsequently I am finding nuts like these throughout the Valley and on multiple cultivars. A few field consultants have reached out with photos of nuts showing similar symptoms. I would strongly encourage field consultants to submit samples and please let me know what you find.

In the 2021 growing season I found Xanthomonas in the receptacle of the husk (creating a similar symptom) and staining nut shells, but kernels were unaffected in that case. I’ll address that in another post.

Early nut cluster of ‘Yamhill’ showing symptoms. Photo: Nik Wiman
Multiple clusters showing symptoms. Photo: Nik Wiman
Severe decay on this nut in a cluster of ‘Yamhill’. Photo: Nik Wiman
Note decay on the husk receptacle where it meets the basal scar of the nut. Photo: Nik Wiman
Watersoaked lesions and decay on nuts of ‘Yamhill’ caused by Pseudomonas syringae. Photo: OSU Plant Clinic.
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Rusty Tussock Moth in Hazelnuts

We have noted the presence of rusty tussock moth (Orgyia antiqua) feeding in our hazelnut plots for the last two seasons. This insect seems not to be a pest, only an incidental feeder that causes minor defoliation.

The larvae are quite colorful and showy, with clumps of bristles (setae) on their backs. These bristles are used to convey defensive toxins to predators. The adult moths are interesting. Similar to winter moth, which is another pest of hazelnuts from a different family of moths, the adult female is flightless. The females do not stray from their cocoons, rather they wait for males to locate them by flying along pheromone trails and then they lay their eggs (several hundred) on the cocoon after mating.

This species is exotic to Oregon and it is unclear when it was naturalized. In the UK it is known as the Vapourer moth. We have yet to see an adult moth in the orchard.

Late instar larvae of rusty tussock mopth, Orgyia antiqua feeding on hazelnut. Photo: Nik Wiman
Early instar of rusty tussock moth, Orgyia antiqua, from a hazelnut orchard. Photo: Nik Wiman

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