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.
Production levels with no sucker controls compared to single trunk
Grafting to reduce suckering
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.
1.A.ii. Aphid biological control Growers should be aware that filbert aphid used to be far more problematic before the parasitoid wasp Trioxyspallidus 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.
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 Accumulation
Appropriate organic materials
Products 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)
Products with larvicidal activity (kills larvae/worms) should be applied just prior to first egg hatch (955 DD)
Peak moth emergence should be reflected in peak trap captures.
Reapply ovicidal/larvicidal products
Some larvae will already be in nuts and cannot be managed by this time.
Appropriate timings for organic filbertworm sprays.
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 USPest.org.
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.
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.
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.
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.
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.
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.
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.
Fully developed filbertworm egg with neonate larva ready to hatch. Photo: Erica Rudolph
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.
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.
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.