June 3, 2021 Ontario Hazelnut Crop Update

Welcome to the first instalment of the 2021 Ontario Hazelnut Crop Report from your OMAFRA tree nut team: Jenny Liu, Maple, Tree Nut and Agroforestry Specialist and Melanie Filotas, Horticulture IPM Specialist! We aim to post every few weeks during the season with status updates of hazelnut production and pests around the province.

New Tree Nut Production Specialist

I’d like to take a moment to introduce myself. My name is Jenny Liu and I started in January as the new Maple, Tree Nut, and Agroforestry Specialist at OMAFRA. As many of you know, Todd Leuty, the previous specialist in this position, retired last September after over two decades of dedicated public service. His contribution to the maple and tree nut sectors cannot be understated, and he certainly left behind some enormous shoes to fill!

A bit about me – I completed my forestry undergraduate degree at the University of British Columbia, where I worked in forest management, dendroecology, and forest pest research. I then set my sights on agriculture, earning my Master’s in agricultural entomology at the University of Guelph. I am also a Certified Crop Advisor Candidate with agronomy experience in both Ontario’s field and horticultural crop sectors. My hobbies include hiking, mooning over houseplants, and designing ambitious crochet/knitting projects that I slowly follow through with. It is really a dream role for me to learn about how trees grow and to share that knowledge.

Please feel free to get in touch –

Phone: 519-835-5872

Email: jenny.liu2@ontario.ca

Under non-COVID circumstances: Guelph OMAFRA Office

Hazelnut Development Update

As of June 1, hazelnuts are all leafed out, and nut clusters are just beginning to develop on early varieties. Growers in the south are reporting much drier conditions than usual, with May rainfalls at low levels not usually seen until July and August. Some growers in the region south of Kitchener to Simcoe got their first rains of May on May 31st. Irrigation systems are working overtime.

There were very few visible signs of frost damage from the cold weather last week, apart from some leaf lightening. Some growers noticed general mortaility in their first year plantings after the frost events in April. Time will tell if the frost events of the past two months will have an effect on yield in older orchards.

Hazelnut Pest Update

Hazelnut Pest Control Products – Crop Protection Guide Now Available

For an current list of pest control products registered on hazelnuts in Ontario, OMAFRA Publication 360E, Crop Protection Guide for Tree Nuts is now available for download or purchase through Service Ontario. This is part of a series of 5 stand-alone crop protection guides:

  • Publication 360A, Crop Protection Guide for Apples
  • Publication 360B, Crop Protection Guide for Berries
  • Publication 360C, Crop Protection Guide for Grapes
  • Publication 360D, Crop Protection Guide for Tender Fruit
  • Publication 360E, Crop Protection Guide for Tree Nuts 

Download your copies free here.

Print copies are also available to order from ServiceOntario Publications for $10 each or $35 for kit of all 5 plus shipping and handling.  Order online at Ontario.ca/publications or by phone 1-800-668-9938 Toll-free across Canada.

Gypsy Moth

This certainly appears to be the year of the insect in hazelnuts.  Gypsy moths are now dispersed and feeding on a wide variety of tree species across the province. According to the Ontario Ministry of Natural Resources and Forestry last year was a record-breaking year for gypsy moth defoliation in Ontario, with over 600,000 ha defoliated in 2020, well over the previous record of 350,000 hectares in 1991. OMNRF has predicted moderate to severe defoliation for 2021 in gypsy moth hot spots.  Hazelnut growers in many areas across the province have reported significant gypsy moth infestations. 

Gypsy moth feeding initially resembles small holes but the area consumed increases as they mature. The larval host range is large, but hazelnuts are one of their preferred host species and based on previous years, growers can expect significant defoliation without intervention. Mature hazelnuts with significant leaf area may be able to tolerate some level of defoliation, however young orchards can be completely defoliated as gypsy moth caterpillars mature, which can lead to reduced growth and increased stress of developing trees.  Based on current levels of infestation, it is likely that most orchards with gypsy moth present will require some level of control.

Gypsy moth caterpillars at the Simcoe Research Station hazelnut orchard on June 1, 2021. These larvae are developing rapidly and will soon develop their yellow head. Larval feeding also removes more and more leaf area as larvae increase in size.

In very small orchards with small trees, larvae can be handpicked and crushed. It is also possible to install a burlap skirt at the base of trees to create a shady, protected area for larvae to hide under during the day. These skirts need to be inspected daily, when larvae are hiding, and the caterpillars removed and destroyed. However, these cultural practices are likely to be impractical in larger orchards.

There are no pest control products specifically registered for gypsy moth on hazelnuts in Ontario, however products registered and applied for leafrollers (see below) should also provide control of gypsy moth. Products based on the biological insecticide Bacillus thuringiensis (BT) (Dipel, Bioprotec, Xentari) can be quite effective if applied when larvae are small. These products must be consumed by the larvae to be effective, so should be applied close to the time that larvae are actively feeding, and good coverage of all leaf surfaces are required.

Once larvae have developed yellow heads and are longer than 2.5 cm Bt-based products are much less effective and alternate controls will be required. At the Simcoe research station, larvae are approximately at the third instar stage (see below), and likely have only a few days before they reach this less susceptible stage.

Further complicating control is that gypsy moth larvae do not all hatch at once, so they may arrive in orchards multiple times, prolonging the period over which control is required.


As if gypsy moth were not enough, other caterpillars are also feeding on hazelnut leaves at this time. Leafrollers, in particular the obliquebanded leafroller (OBLR – Choristaneura rosaceana)and the fruit tree leafroller (Archips argyrospila), are present in higher than normal numbers in some hazelnut orchards. Leafrollers feed on many fruit tree species and can be distinguished by their habit of rolling leaves over themselves with webbing to create a shelter. Larvae feed on leaves, and typically defoliation is not as significant as from gypsy moth. However when leafroller feeding occurs adjacent to developing fruit, they can move onto fruit, causing indentations and scars. Scarring and staining of shells under husks has been reported for OBLR in Oregon hazelnuts. Many leafroller species will be nearing pupation, however some (including OBLR) will have a second generation later in the summer.

Look for rolled leaves especially at the terminals of hazelnut branches. These can be unrolled to reveal webbing, frass (excrement) and often the larvae themselves. Leafrollers have light to dark green bodies with a dark brown to black head, and may wriggle backward when disturbed.


Leafroller larvae on hazelnut leaf
Unrolled leaf showing webbing and frass.

To determine how significant an issue leafrollers are in your orchard, you can try examining 10 terminals per tree on each of ten trees and recording presence of damage, rolled leaves and larvae. There is no threshold for leafrollers on Ontario hazelnuts, however in Oregon hazelnuts, a threshold of 20-25% of terminals infested is used. This can serve as a guideline, but may not apply specifically to Ontario. Note also that if trees are also infested with gypsy moth and/or they are very small, then a lower threshold should be used.

For a full list of products registered for control of leafrollers on Ontario hazelnuts, refer to OMAFRA Publication 360E.  Note that as leafrollers become larger and approach pupation, BT-based products may be less effective.

Aphids and Scale

Aphids and scale are also present in larger than normal numbers in some hazelnut orchards. Aphids are soft-bodied sucking insects found in colonies on the undersides of hazelnut leaves, particularly young leaves and succulent shoots. They are often yellowish, and can be distinguished by the presences of 2 “exhaust pipes”  called cornicles at the rear of their abdomen.  Aphids move into orchards as temperatures warm in the spring and settle on leaf undersides, where they feed and produce nymphs. There are multiple generations throughout the season.

Lady beetle larvae feeding on aphids. Larvae are sometimes mistaken for gypsy moths, but have distinct legs and different colouring.

Scales on hazelnuts are typically the European Fruit Lecanium, and are also sucking insects, which form a shell-like, waxy coating to cover their bodies and eggs. Scales overewinter as nymphs under the protective hump-like covering on twigs and branches of hazelnut trees. In spring they become adults and lay eggs under the covering after which the adults die.  At this time in Ontario hazelnuts, scales are at the egg stage, under protective covers.  These eggs will hatch in the next few weeks, producing tiny crawlers that will move to leaves to feed.

Lecanium scales settle on hazelnut twigs and shoots and from protective coverings that look like brown bumps.
Lecanium scale eggs laid under the shell of the female scale
Eggs under the shell of the female lecanium scale (Source: University of Minnesota)

Both aphids and scales drain fluids and nutrients from hazelnut leaves and buds. While they are often kept in check by natural enemies, if aphid populations get high enough, they can cause distortion and wilting of leaf tissue, and even reduce nut fill and size. Heavy feeding by scale can also kill twigs, reduce growth and fruit size and weaken trees.   Both insects also excrete large amounts of a sticky, sugary fluid, which can cover leaves and promote growth of sooty mold fungus.

As with most insects, there are no established thresholds for aphids on Ontario hazelnuts. In Oregon hazelnuts, a threshold of 30 aphids/leaf in May and 40/leaf in June after checking 3 leaves/terminal on 3 terminals/tree on 20 trees would warrant control. This should only be used as a guideline, and you may want to adjust this based on your experience with aphids, the number of beneficial insects (e.g. ladybeetles, signs of aphid parasitism) and other stresses to your trees. Increasing populations of aphids from week to week, particularly without an increase in beneficial insect activity, might also indicate control is warranted. There are a variety of products registered for control of aphids on hazelnuts – refer to the Hazelnut Calendar of Publication 360E for options.  However, some products are more harmful to beneficial insects than others. Growers can refer to Table 3-11, Toxicity of Pesticides to Honeybees and Mite/Aphid Predators of Publication 360E to help select products that can preserve beneficials which will help keep pests under control in the orchard.

For scale, hazelnut trees appear to be able to tolerate a few scales with no issues, particularly with lots of natural enemies present. With very heavy infestations, particularly if trees are stressed by other pests, control may be required.

It is important to be aware that scale controls will be ineffective if applied at this stage, when unhatched eggs remain under the shell, because pest control products cannot penetrate the protective covering. If an insecticide is required, this needs to be applied once eggs have hatched and crawlers have left the shell to feed on the leaves. This will likely occur within the next few weeks in most southern orchards.

That concludes this edition of the Hazelnut Update. If you wish to provide information for future updates, contact jenny.liu2@ontario.ca (production), melanie.filotas@ontario.ca (pests) or comment on this post. 

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1 Response to June 3, 2021 Ontario Hazelnut Crop Update

  1. Les High says:

    Well covered. I’ll look a little harder on my next walk. Jenny made the rounds with me a couple of days back and didn’t point out ant impending disaster. Hope that continues. I expect Japanese beetle won’t bypass me though.
    Nutlets starting to appear but expect others to show within 2 weeks.
    Les at Jordan Station, Ontario

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