Pest Alert: California root borer in hazelnuts

A few years back we were trying to attract flatheaded borers (Buprestidae) to traps when we realized another borer pest may also be problematic in hazelnuts. Working with a pheromone company (AlphaScents, Canby OR) we deployed some pheromone of the California prionus beetle in an orchard that was exhibiting symptoms of decline. We started catching high numbers of Prionus californicus males, up to 25 per trap per week. That is a lot of biomass as these are huge beetles, adults can be 3.5 inches long. While we occasionally dig one up when investigating hazelnut root problems, we had not really had growers complain.

That changed in 2022 when reports of these root borers causing severe tree decline and death started coming in. This year, the problem seems to have exploded with many growers losing production age trees to the borer. Not just a few. Significant numbers of trees and it is clear from these sites that the problem is spreading and getting worse.

Severely affected trees had difficulty leafing out and are now showing signs of die back. Some trees were nearly dead. On all of these trees, there was a lot of sign of borers right at the soil line. Stripping some bark at the base of the tree may show larval galleries packed with sawdust and this is a good indicator that the root system of the tree may also be infested. Some of these same trees also had flatheaded borer damage up higher in the tree. Usually, flatheaded borers are more of a problem on young trees, but in this situation they are attacking major scaffold branches and the trunks of 5-7 year old trees.

A horizontal slice of the root crown shows numerous sawdust-packed galleries (the light colored spots). No wonder this tree was having issues (NGW).
As the larvae mature, larger roots are girdled (NGW).
Larvae are well above ground in this hazelnut stem (NGW photo)
Steven Valley, Oregon Department of Agriculture,
Creative Commons License   licensed under a Creative Commons Attribution-Noncommercial 3.0 License.
Steven Valley, Oregon Department of Agriculture,, licensed under a Creative Commons Attribution-Noncommercial 3.0 License.
Good sized larva (grub) excavated from root mass. N Wiman.
Mature larva (grub) of Prionus californicus pulled from an old walnut root crown in the author’s hand. Besides being much larger, California prionus is a roundheaded borer and lacks the flattened thorax of flatheaded borers.
Decline symptoms on a tree that has been attacked by root borer larvae (NGW photo).
Stripping bark at the base of the tree showed many galleries from very young larvae and this may be a good indicator of infestation (NGW photo).
Tearing out a tree. This tree was riddled with both flatheaded and root borers (NGW photo).
Young Prionus larvae pulled from this hazelnut trunk base (NGW photo).

Management of this pest is challenging. The lifecycle is long, lasting 3-4 years for the larvae below ground. It is thought that young larvae may affect more of the peripheral feeder roots with convergence on the crown as they mature. We are also seeing a lot of larvae above the root crown around the base of the tree. Insecticides are not incredibly effective, but there is a consensus that imidacloprid (Admire Pro, Generics) applied to the soil or through injection may help if applied over multiple years. Insecticide residues on trunks may also deter ovipositing female borers or may kill eggs and newly emerged larvae. The adults are short lived, and are thought to be active from July to August. They have non-functional mouth parts (they don’t feed) and their singular mission is to mate an lay eggs. Females call males using a sex pheromone, which has been commercialized. This allows a mass trapping approach for management. If used consistently over multiple years, mass trapping can remove a significant number of males from the local population, which can reduce female mating success and pest pressure. We have had good luck with baited panel traps hung low from trees (see suppliers). Males are good fliers and are super sensitive to the pheromone. A low density of traps will effectively trap a large area.

Cherries, pecans, hops are other specialty crops that are also affected by this pest. So we are not alone. Pest management experts from those industries may have additional insights.

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Heat and sulfur burn in hazelnuts

A few years ago, the Oregon hazelnut industry added a new tool to use against big bud mite: micronated dry flowable sulfur. There are several special local needs labels for different brands that you can find in the Hazelnut Pest Management Guide. There are at least two bud mite species that affect Oregon hazelnuts; Phytocoptella avellanae and Cecidophyopsis vermiformis. These mites originated from Europe/Eurasia and probably arrived in Oregon on the first nursery stock of European hazelnut that was imported. They cause galls to form in buds, which are highly apparent in spring. The galls often kill the buds and they fall from the tree, leaving blind wood. Sometimes the infested buds are able to successfully develop, but growth may be abnormal. Some hazelnut varieties are resistant and never have any issue, but others that are widely planted are highly susceptible.

The use of sulfur replaced some of the older, more broadly toxic chemistries, and the dry flowable (DF) formulation can be easier to use than lime sulfur products and is cheaper than some of the other miticides. We used it successfully in multiple trials with no problems and we got decent control. The residues can be long-lived on the foliage, which helps with timing the applications to coincide with the spring mite migration, which is the hard-to-predict vulnerable period when the mites leave the galls and migrate to new axillary buds on developing shoots.

The downside of sulfur is that it can burn in hot weather (read your labels!). We found this out big time in the heat dome of 2021 (June 24-29) when it reached 116 F for three consecutive days in the North Willamette Valley. Trees that had not been treated in weeks had severe burn and defoliation. Luckily we caught this in our trial and we saw no burn from single applications of up to 15 lbs, but severe burn from two applications of the 10lb rate. We noted from growers that high rates of sulfur DF and multiple applications caused severe burn in some orchards. There may have been some interaction with adjuvants as well.

With hot weather up ahead and bud mite management season upon us, I just wanted to throw this reminder out there, use caution! If there was a silver lining, the heat (and perhaps the burn) definitely set the mites back. We had not a single blasted bud in our trial orchard the following spring of 2022 and it has taken until 2023 for the mite populations to recover.

Bud mites in hazelnut, at left a galled “blasted” bud, center close up of the gall, and at right bud adults under magnification in the gall. All photos N Wiman.
Foliage from untreated control trees, sprayed with water only on April 21, 2021. Photo taken after the heat dome event on July 1.
Foliage from trees sprayed with 15 lb micronated sulfur DF on April 21, 2021. Photo taken after the heat dome event on July 1. Note some burn but this was the worst of it.
Foliage from trees sprayed with 10 lb micronated sulfur DF on April 21 and May 5, 2021. Photo taken after the heat dome event on July 1. Severe burn resulted.
Foliage from trees sprayed with 10 lb micronated sulfur DF on April 21 and May 5, 2021. Photo taken after the heat dome event on July 1.
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Low heat units indicate late start to 2023 season

Winter is holding us tight this year in the Willamette Valley, but it may be finally losing its grip. A break in the rain and warmer temperatures in the forecast will be a relief for hazelnut growers with orchards susceptible to eastern filbert blight (EFB). Rain spreads the spores of the fungal pathogen Anisogramma anomala to the susceptible meristem tissue as the trees break bud an enter the shoot elongation phase. It has been difficult to find a break in the rain to get the necessary fungicides applied. More than 5 inches of rain have fallen since April 1 at the North Willamette Research and Extension Center in Aurora.

Its not just the rain, it has also been very cool in the Willamette Valley with low elevation snow levels and late freeze events. So how far behind are we on heat unit accumulation? The table below indicates that growing degree days (lower threshold 50o F) accumulated since January 1 are running roughly a month behind last season, and 3 weeks behind the 30-year normal on average across 4 sites in the Valley. Expect pests like budmite and filbertworm to be later (but not aphids) and it could be another late hazelnut harvest. Time will tell if we can catch up, but right now it looks like another late year.

Late blooming almonds in a research trial at the North Willamette Research and Extension Center typically bloom at the end of March, but didn’t bloom until mid-April in 2023.
Hazelnuts in the Willamette Valley are still pushing leaves from buds and leaves are expanding. Orchards have been very wet, and orchard access has been difficult this spring. Some growers have been waiting for a weather break to plant new orchards so there will be some late plantings.
Accumulated growing degree days (GDD; base 50 F) at Willamette Valley weather stations. Degree day heat units drive development in plants, insects, and other organisms that depend on heat from the environment to drive metababolic processes. The degree day calculator at can be used to calculate GDD.
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Hazelnut aphids are out

We have been noting aphid emergence over the last two weeks, but there remain a lot of unhatched eggs around the buds and on the bark.

The unhatched eggs remaining may be primarily filbert aphid, Myzocallis coryli, as most of the aphid nymphs seen so far are hazelnut aphid, Corylobium avellanae. Hazelnut aphid in these images is easily distinguished by the presence of well-developed cornicles, which are the tubes emerging from the back of the abdomen. So far, we have not come up with a reliable method to differentiate the eggs of the two species either by location on the tree or by egg morphology.

We are somewhat mystified that we are seeing such a predominance of hazelnut rather than filbert aphid this year. Our research will provide some clues as to whether there is a biological or environmental factor that is leading to more hazelnut aphids.

Accompanying the emergence of the aphids is the parasitoid wasp Trioxys pallidus. This wasp was imported from Europe to control filbert aphid in the 1980s. The wasp overwinters inside aphid hosts on the tree. These large aphid mummies can currently be found on branches and catkin peduncles. The wasps are already looking for mates and foraging for aphids along branches. While they do fly, they are most commonly seen walking along the surface of the tree.

Immature hazelnut aphids on a floral bud of ‘Jefferson’. Photo: Heather Andrews.
Overwintered mummies of the parasitod wasp Trioxys pallidus. Photo: Heather Andrews.
The parasitoid wasp Trioxys pallidus is an excellent biological control agent against filbert aphid, Myzocallis coryli. Wasps have begun emerging from overwintered mummies. Photo: Heather Andrews.
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Digging trees to determine nitrogen content

Last week the digging and removal of these ‘Jefferson’ trees marked the beginning of the end of a long experiment. Back in April of 2019, we applied some very expensive urea fertilizer around the drip line of theses trees. The cost at that time was not due to supply chain issues, but because we applied 10% 15N urea, a special urea containing the stable isotopic form of nitrogen.

Isotopic 15N is rare in nature and has a higher atomic mass (due to an extra neutron) from the more abundant form of N. Isotopic 15N can act just like regular N as a nutrient in plants and animals, but it can be detected in laboratories that specialize in isotopic analyses. This allows researchers to use the 15N as a tracer. When applied as fertilizer, we can follow to movement of 15N into the plant. This can be used to better understand uptake of N and subsequent partitioning of N to different parts of the tree over time because we know when and where and how much 15N was applied.

In our research, we wanted to determine how the uptake of the isotopic 15N urea would be affected by irrigation, and where the N would move once it was in the trees. Irrigation did have a major influence on uptake and we were surprised to find that the soil-applied isotopic N made it into tissues such as leaves, shoots, nuts and catkins within a year. We are currently working on final analysis and publication of the study results. One major task remains- destructively harvesting the trees.

Destructive harvest is necessary because for most tissues we only know the percentage of N and percentage of isotopic 15N. Now, in order to determine how much N is stored in the trunk for example, we need to determine how much biomass different tree structures contain. So now we need to break down the trees into different parts such as trunk, roots, young branches, scaffold branches etc.

Did you know a 6-year-old tree can more than 3 lbs of catkins?

Thanks to the Oregon Department of Agriculture Fertilizer Program for supporting our study.

The Orchards Team starting to dig out the trees.
Adding some machine muscle with the backhoe.
Mostly intact root systems, but we will never know how much fine root structure we lost.
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Aphid oviposition (egg-laying)

In recent days you may have noticed that there are suddenly a lot of aphids in the orchard. Aphid populations typically enjoy the period after nut drop. The weather cools down, and aphid populations spike. One last hurrah before winter. However you might have noted something odd about where the aphids are within the trees right now. Not only are they crawling all over the leaves, but they are all over the wood, particularly the older wood. Normally aphids are found on leaves and husks and shoots, the green plant tissue where they can access and feed on the phloem, not on the bark of the scaffold branches. So what is going on here?

It turns out we have reached an interesting point in the life cycle of the two aphid species that are important on hazelnuts, filbert aphid (Myzocallis coryli) and hazelnut aphid (Corylobium avellanae). This is the one and only sexual stage. Both of these aphids overwinter in the egg stage. In the spring the eggs hatch and the tiny aphid nymphs begin feeding on the buds as they swell. But in the fall, the vegetative tissues that aphids feed from all growing season such as leaves and husks, fall from the tree and they compost on the orchard floor. Thus, these green tissues are not suitable for egg laying and the aphids have adapted to laying their eggs in the rough bark of the 2+ year old wood. The eggs are green at first but then ripen to a shiny black color.

For most of the growing season, adult aphids reproduce asexually by giving birth to live young. This sexual stage that produces the eggs is unique. For the sexual females to produce the eggs, they must first mate with the winged sexual males. You may see some of this going now on if you inspect leaves.

Female filbert aphids laying their eggs. Photo: NGW
Aphid eggs are pale green ovals and they ripen to become shiny and black. Photo: NGW
Winged male filbert aphids mating with the apterous (wingless) sexual females on leaves. Photo: NGW

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Organic production research – Orchard Crops Research and Extension Program

Organic Hazelnut Farm Tour E-Handout, Aug. 19, 2022

Nik G. Wiman (+ Team), Orchard Specialist & Associate Professor


  1. Organic Pest Management
    1. Aphids
      1. Aphid management tactics
      2. Aphid biological control
    2. Filbertworm
      1. Organic sprays
    3. BMSB
      1. Organic sprays
      2. Biological Control
  2. Cultural Practices
    1. Production levels with no sucker controls compared to single trunk
    2. Grafting to reduce suckering
    3. Cover crops – new soil health project

1.A.i. Aphid managment tactics. Aphids may not normally be a problem in organic hazelnuts. In an older study that took place in unsprayed hazelnut blocks, aphids were not a pest, the populations were kept at low levels by the natural enemy community. However, certain organic insecticides that are used to control pests such as filbertworm (such as spinosad) can be disruptive to the natural enemy community and can increase risk that aphids will become problematic. Aphids can impact yields (reduced fill) and impact tree health and vigor. There are two species that affect hazelnuts; filbert aphid (Myzocalis coryli) and hazelnut aphid (Corylobium avellanae).

Both species spend the winter as eggs on twigs and branches and begin hatching around budswell. As they hatch they begin feeding on the buds, before moving to the underside of the leaves. At that point, the two species begin to occupy separate niches, with the filbert aphids staying on the leaves, and the hazelnut aphids start moving on to the leaf petioles and shoots and eventually hazelnut aphid move to the husks. As soon as these overwintered aphids make oit to the adult stage, they start giving live birth to nymphs and populations increase rapidly.

While OSU has developed thresholds for treating aphids based on the number of aphids per leaf, we wanted to try some other tactics. Instead of waiting for aphids to increase, could we spray organic crop oils to knock back the aphid populations early in the season before the natural enemy community becomes active? We have had good success with this tactic. Oils smother aphid eggs and early nymphs. We hope to see superior spray oil be registered for hazelnuts as it will be very useful for organic growers. Meanwhile botanical oils (such as neem) can be used for organic and there are a number of these registered for use in organic hazelnuts. A big question for this research was regarding the safety of using oils on hazelnuts because they are not widely used, but we have not seen any phytotoxicity issues.

Initial egg hatch occurs at budswell. Photo: Heather Andrews
Hazelnut aphids are segregated along the stems whereas filbert aphid is more concentrated along the lateral and mid leaf veins.
Extreme infestation of hazelnut aphid on husks. Photo: Heather Andrews
Botanical oils (Rango and AzaDirect are registered for organic use and are neem products) did a good job in reducing initial aphid problems without impacting biological controls (data not shown) up to at least 14 days after treatment (DAT) when applied at budswell on ‘Jefferson’. Superior mineral oil is also effective but is not yet registered for use in hazelnuts although it is an organically acceptable oil in other orchard crops. Results from new trials are evaluating entomopathogenic fungi and some other organic materials for aphid control coming in 2023. Thanks to Oregon Hazelnut Commission for support of this work.
Trioxys wasp attacking filbet aphid on a leaf. Video: Erica Rudolph.
Filbert and hazelnut aphid abundances over 2020 season.
Lacewing activity was highest mid-season in 2021 and 2022.
Spiders were surprisingly consistently abundant across the season.

1.A.ii. Aphid biological control Growers should be aware that filbert aphid used to be far more problematic before the parasitoid wasp Trioxys pallidus was imported from Europe and released in the 1980’s. As a parasitoid, this tiny wasp stings the aphids and lays its own egg inside. Once the larva completes development in the aphid, turning it into a “mummy”, a new adult wasp emerges. Mummies are swollen brown aphids and are a sure sign the wasp is at work.This wasp resulted in a major decline in insecticide use against filbert aphid after its introduction.

Since the introduction of the wasp, the hazelnut aphid was also introduced and aphid problems seemed to worsen. While the natural enemy community of filbert aphid was thoroughly studied in the 1980’s, little work has been conducted since and very little information exists about hazelnut aphid natural enemies. We are now in the third year of an intensive study of the phenology of both aphid species and the natural enemies of these species. This will help us understand how best to enhance biological control and understand any shifting dynamics in the natural enemy community. We have made some exciting discoveries along the way including some important new natural enemies. Thanks to the OHC for supporting this research.

These brown swollen aphid mummies on twigs and catkins are how Trioxys overwinter. Photo: Heather Andrews.

1.B.i. Filbertworm organic sprays. Filbertworm can be a challenging pest for the organic grower. There are few organic options that are truly effective, and the materials can be be expensive. A diverse approach will be most successful. Mating disruption with meso dispensers can be helpful. Apply dispensers before moths begin flying in the upper canopy. Disruption will be most effective on larger orchard blocks that have a high ratio of core to edge and a low to moderate population of filbertworm.

There are relatively few spray treatments that are effective. To make these work as hard as possible, you will need to have good timing, so proper use of the phenology model and trap threshold methods is very important. Organic materials target eggs and the freshly hatched larvae, but may cause some moth mortalilty.

Some good treatment options are:

Entrust (spinosad) – Probably the most relied upon material for organic growers. It has many desirable qualities and it is relatively safe for the environment and the applicator. It does have some broad-spectrum activity and can harm beneficial insects. It can act on moths and larvae. Apply at first egg hatch.

Surround (kaolin clay) – I see very little use of Surround in hazelnuts in the Willamette Valley. It does turn trees white, which will definitely attract attention (from human neighbors). However, it can be an effective deterrent for filbertworm and also BMSB. It is a particle film, not an insecticide, so you can’t expect 100% control. But it does have a significant effect, consider using it as part of your overall management strategy. It is a bit hard to keep in suspension for spraying, agitation is key. It does not harm the tree, in fact it can help trees resist drought stress. It washes off the tree and nuts with water, perfect for use against filbertworm in the dry season. Reapplication are necessary to maintain coverage, applications can begin prior to egg laying.

Grandevo (chromobacterium) – We have seen it work effectively, and we have some new trials with it. Marrone (the manufacturer) has new formulations.

Oils – Oils can be very effective for smothering eggs. There are a number of oils that are available to organic growers. These are botanical or vegetable oils. Light oils are preferable and will be least likely to damage leaves. Superior 440 mineral oil is ideal, but not yet registered for organic or conventional. Read labels carefully about applying oils in-season (as opposed to dormant). Time these for first egg hatch or max eggs.

Other organic-compatible materials:

Bacillus thuringensis Kurstaki (BtK) – BtK is a fantastic material for leafrollers but will not be effective on filbertworm.

Pyganic (pyrethrins) – although this is a great natural knockdown material it has virtually no residual activity and will not be very effective on filbertworm.

Virus (codling moth granulosisvirus, Cyd-X and others) – experimental only. We think it works and we hope to have it registered some day soon.

Filbertworm Degree-Day AccumulationApplication NotesAppropriate organic materials
815-955Products with ovicidal activity (kills eggs) are applied between first egg laid and first egg hatch (815-955 DD)Oils and Surround (reapply according to label or coverage)
955Products with larvicidal activity (kills larvae/worms) should be applied just prior to first egg hatch (955 DD)Entrust
1188Peak moth emergence should be reflected in peak trap captures.
1393Reapply ovicidal/larvicidal productsEntrust
1533Some larvae will already be in nuts and cannot be managed by this time.
Appropriate timings for organic filbertworm sprays.
‘Yamhill’ tree treated with 2 applications of Surround kaolin clay. Photo: Nik Wiman
Nut cluster coated in kaolin clay. This helps protect the nuts from pests like filbertworm and BMSB. Photo: Nik Wiman

To get the best timing out of the filbertworm model it is ideal to have your own in-orchard weather station and enter the data into a degree day calculator using max and min temperature after April 1 with a lower threshold of 50 degrees F. Some of the companies that sell weather data services can set up your weather data feed to calculate the model automatically. If you don’t have on-farm weather, try the custom CropConnect website to find the location nearest to your farm. One final option is to select a public weather station and filbertworm model from

Traps are very useful to check against the model or the trap threshold method can be used. Place traps at roughly 1 per 2.5 acres in the upper 1/3 of the canopy. If you average 2-3 moths per trap or have 5 or more in any single trap treat 8-12 days later to target the hatching eggs produced after the moths mate and lay eggs.

BMSB nymphs feeding on ‘Yamhill’ nut clusters from mid August 2022.

1.C. BMSB Management. BMSB populations are high this season. For organic management Surround may be the best option. We are currently evaluating some promising alternatives.

Trissolcus japonicus, the egg parasitoid, is becoming widely established in the Willamette Valley.

2A. Cultural Practices-Production levels with no sucker controls compared to single trunk. Organic growers are particularly challenged by suckers. One of your research questions is: Are multistem plants or hedgerows a cheaper, more productive method of production?

In a long-term study from the 1960’s, multistem hazelnut trees produced not as well as single trunk and were more challenging to harvest. Hedgerows were highly productive but were not monitored long-term. Over-the-row harvest could be a good option if hedgerow trees can be maintained at a small size.

Our study is designed evaluate production of 3, 6, and 8 ft spacing of trees, with sucker control on half of each treated block. Summer pruning is used to keep higher density trees smaller. Research is in the initial stages.

Hazelnut plot designed for evaluating high, medium, and low density hazelnut systems and multi-stem production at the North Willamette Research and Extension Center in Aurora, OR. Photo: Nik Wiman
Classic study by Harry Lagerstedt on tree spacing and training in Oregon.
Study results comparing single trunk to muti stem production levels.
High density hedgerow of ‘Jefferson’. Photo: Nik Wiman
‘McDonald’ scion was hot callus grafted to ‘Dorris’ rootstock, one of the smaller trees in the OSU lineup.
The ‘McDonald’ scion appears to be growing quite well on ‘Dorris’.

2B. Cultural Practices – Grafting to reduce suckering. One objective of this project is to evaluate potential use of OSU hazelnut varieties with genetic resistance to eastern filbert blight as rootstocks. Among the characters we are looking for in the rootstocks is reduced suckering. Of course there must also be good compatibility between the scion production variety and the rootstock. Special thanks to Bruck Nurseries, our major collaborator for this project. We are just getting to the point where we can evaluate some of the rootstock effects.

‘McDOnald’ on ‘Felix rootstock.
Lacy Phacelia can be a a good cover crop for hazelnut headlands and alleys. Photo: Nik Wiman

2C. Cultural Practices – cover crops and soil health. The Oregon Specialty Crop Block grant program recently awarded our team with a grant to study barriers to cover crop adoption and soil health benefits of cover cropping in hazelnuts. We need research sites, please contact me if you are willing to allow some research in your orchard where you are using cover crops. Blocks need not be organic.

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Field grafting hazelnuts

Cleft grafts on Jefferson where the intent is to convert the tree to a new variety conserving some of the branching structure on smaller caliper wood. Grafting and photo by Kody Transue.
All scaffolds of Jefferson grafted with two scions, with suckers left to nurture the tree (equivalent to nurse limbs). These can be removed later. Grafting compound had to be reapplied due to excessive rain. Grafting by Kody Transue.
Rind or bark grafts on main trunk. Grafting by Kody Transue.
This photo of a healing rind graft with a nice shoot is from early Aug. Photo Nik Wiman.
These scions were probably not long enough, often buds died near the tips and the buds close to the graft survived. The constant rain washing off the grafting compound didn’t help either. Photo: Nik Wiman.

Field grafting of hazelnuts has been practiced for many years in Oregon but is not a widespread or common practice. Some in the industry such as David Smith of the OSU Hazelnut Breeding Program have a wealth of knowledge on the practice. Probably the most common application for field grafting has been to correct issues with pollenizer trees in an established orchard. To compensate for lack of compatible pollen, improve spatial distribution of pollen, or to simply bring in some new sources of pollen, individual scaffold branches are grafted over to the new pollenizer variety. This technique also allows a single tree to become a source of different pollen types for the production trees.

The document EM9075 from the OSU Extension Catalog by the late Jeff Olsen and David Smith has a small section on field grafting techniques. Hazelnuts are somewhat tricky to graft compared to fruit trees like apples, and the Extension document notes that results are not always completely satisfactory. One of the issues noted in EM9075 is that hazelnuts can push a lot of sap against the graft, preventing good take. Field grafting must be performed when there are shoots with leaves on the rootstock (nurse limbs) to absorb sap pressure so that grafts are not overcome by sap. That means shoots of the rootstock must be leafed out and conserved until the scions are established enough to nurture the tree. In contrast, the scions should be in a completely dormant state at the time the graft is made. The scion is collected mid-winter and held under cold storage. Conditions at the time of grafting can’t be too hot or the scions will dry out before they have enough vascular connection with the root stock to support the leaves. Moderate warm temperatures around 70 F in mid April to mid May are ideal, but this season (2022) was very cool and we didn’t get our grafts done until mid June and we still had decent success.

As our hazelnut industry continues to expand and we produce more and more varieties, there is increasingly a need to improve field grafting knowledge. As EM9075 notes, field grafting or top-working is common practice in other orchard industries and it is well established that a field grafted tree will grow much faster and be back in production much sooner than a replant. Some growers have expressed interest in converting an orchard of one variety to another that pays more. We also need more information about how different rootstocks affect characteristics of the scion. Are there blooom timing effects? Yield effects? Nut character effects? Does the rootstock influence nut drop timing? Conversely, do some of our varieties have certain characters that make them better than others as rootstocks? Bench grafting can also be very useful to evaluate some of these effects and this is another aspect of our research. More on this in future postings.

Regardless of the desired outcomes, knowledge on field grafting needs to develop in the hazelnut industry. At the North Willamette Research and Extension Center, we have begun a series of grafting experiments including a row of Jefferson that we will likely expand on for the purpose of documenting long term success of different field grafting techniques. Kody Transue is a skilled grafter on our team that will be doing the actual grafts and some of his work from this year is highlighted at left.

Good take on a terminal scion bud with a cleft graft. Grafting by Kody Transue.

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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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