Small holes in the shell of hazelnuts raise alarm bells. The hazelnut borer was at work. You can find out what the term means and how you can recognize the pest and combat it biologically here.
How do you combat hazelnut borers organically?
The hazelnut borer is a pest that attacks the shell of hazelnuts. For biological control, tree shaking, selective harvesting, lime rings, nematodes, as well as chickens and ducks that eat hazelnut borers and larvae are suitable. Early ripening hazelnut varieties are more resistant to the pest.
- Hazelnut borer is a 6-9 mm large, black-brown-white weevil whose reproduction and feeding is dangerous for hazelnuts as well as the buds, flowers and fruits of other fruit trees.
- Females drill a hole in the shell to lay their eggs. Egg and larva development takes place inside a hazelnut from June onwards.
- Effective biological control agents are: shaking off, crop selection, glue rings, nematodes as well as pecking chickens and ducks.
What is a hazelnut borer?
A hazelnut borer is a beetle with a very long proboscis
Hazelnut borer is a beetle from the large family of weevils. Mated females lay their eggs in unripe hazelnuts so that voracious maggots can develop undisturbed in the protection of the shell. After a month, an adult larva leaves the empty shelter, leaving a distinctive hole in the shell. The combination of ruthless reproduction and destructive nutrition has earned the hazelnut borer its reputation as a pest. The following profile provides compact information about beetles and larvae:
| Profile | Hazelnut drill | Larva |
|---|---|---|
| Size | 6-8, 5mm | 12-15mm |
| color | black-white-brown scales | yellowish-white |
| Body shape | oblong-oval | worm-like |
| Special feature | long, dark brown trunk | brown head |
| Nutrition | Fruits, leaves, hazel | Hazelnut |
| Botanical name | Curculio nucum | |
| Family | Weevils |
In-depth information about the profile is provided in the following sections with more detailed explanations of appearance and lifestyle.
Identifying hazelnut borers
Hazelnut borers have a black body, which of course remains hidden from the viewer. A patchy pattern of brown, yellowish and white scales covers the body. It is characterized by a bristly ridge of hair that extends over the elytra suture. The square, whitish scaled label has a bare edge on the side. Red-brown antennae and legs complete the appearance. It is obvious that the hazelnut borer has a trunk that is body-long in females and significantly shorter in males.
The larva, which is up to 1.5 centimeters long, has the typical creamy white maggot look. A strong mouthpart with sharp teeth sits on the brown head capsule. This allows the worms to bite through the hard nut shell on their way to freedom.
Destructive lifestyle of beetles and larvae
The larvae of the hazelnut borer feed on unripe hazelnuts
The following foray through a hazelnut borer year reveals why the beetles are classified as pests:
- Start of activity: from March/April, adult beetles leave their winter quarters in the ground
- Nutrition: Ripening damage to buds, flowers and leaves of cherries, pears, apples, peaches and other fruit trees
- Reproduction: from June onwards, mated females arrive to ripen hazelnuts with a soft shell and 8-12 mm diameter
- Egg laying: Female drills hole in the shell to place an egg
- Egg hatching: within a week
- Nutrition: Larva feeds on the pulp under the shell for three to four weeks
The adult larva enlarges the existing hole in the shell and squeezes itself through. As a rule, the infected hazelnut has already fallen from the tree. This means that the maggot can easily leave its nursery and burrows 10 centimeters deep into the ground, where it pupates and hibernates.
Excursus
Trump card early hazel varieties
Early maturing varieties are the ace up the sleeve of nature-oriented hobby gardeners in the fight against hazelnut borers. In fact, early hazelnut varieties (Corylus avellana) with hard, heavily woody shells are armed against female beetles with eggs in their luggage. Hazelnut borer ladies bite their teeth into premium varieties such as 'Nottinghams Earliest', 'Bergers Zellernuss' and 'Lange Zellernuss', so that egg laying is doomed to failure. Positive side effect: early varieties shine with their distinctive flower catkins as early as February, which the first bees, bumblebees and butterflies really appreciate.
Fighting hazelnut borers – biological remedies at a glance
Once hazelnut borer larvae have taken up residence under the hard nut shell, it is difficult to get rid of the beasts. Effective control must begin where mated females are on their way to lay their eggs or where cunning maggots and beetles lurk deep in the ground. The following table provides an overview of effective pesticides without poison:
| Manual means | Biological agents | Beneficial insects |
|---|---|---|
| Shake it off | Glue rings | Chickens |
| Select crop | Nematodes | Running Ducks |
The competent application of the recommended control methods is explained in a practical and comprehensible manner in the following instructions.
Fighting hazelnut borers manually
Manual control methods stay on the trail of hazelnut borers throughout the season. This procedure does not cost any money, but in return it requires your time and special attention. How to do it right:
Shake it off
- Spread the film under fruit trees (hazel, cherry, apple, peach, pear and others)
- Shake beetles out of the crown from March/April (ideally daily)
- Destroy and dispose of fallen hazelnut borers
The more consistently and regularly you shake affected trees, the higher the success rate. In the early morning hours, most pests fall to the ground because the insects are still frozen from the cold.
Select hazelnuts
Infested hazelnuts should be picked up and disposed of daily
Early in the summer, the first half-ripe and hollowed hazelnuts fall to the ground. If you collect the infected fruits every day, there is a good chance that you will catch the larvae inside. Please dispose of the yield in household waste and not in the compost. Follow this pattern until harvest time. In particular, nuts with a tell-tale drilled hole in the shell are not suitable for consumption and are discarded.
Tip
With a garden close to nature, hazelnut gardeners compete to avoid visiting natural enemies of the hazelnut borer. When no pesticides turn the ground into a toxic minefield, piles of leaves and dead wood remain lying around, and wild fruit hedges invite you to linger, the hedgehog feels warmly welcome. If the cute prickly bear finds a cozy hedgehog house, he will happily settle down and hunt diligently for hazelnut borers and voracious larvae as well as many other pests.
Fighting hazelnut borers biologically
The recommended biological control agents in the table above have a double impact on hazelnut borers. Glue rings target lady beetles as they approach. Nematodes parasitize burrowed larvae in their winter quarters. How to combat hazelnut borers in harmony with nature:
Glue rings
Glue rings are a non-toxic pesticide on tree trunks. A tape coated with glue is placed around the trunk. If hazelnut borers crawl on the bark towards the crown, they stick to the glue ring and die. Equip not only hazelnut trees with the sticky bulwark against pests, but all fruit trees. This is how glue rings achieve the best control success against frost moths, codling moths and other rabble.
You can find out how to attach a glue ring correctly in the following video:
Leimringe an Obstbäumen anbringen - Der Grüne Tipp kompakt
Nematodes
Nematodes are microscopic roundworms that lay their eggs in larvae. This process doesn't end well for the larva. Primarily the nematodes of the genus Heterorhabditis bacteriophoba (HM nematodes) decimate the hazelnut borer population in your garden by up to 50 percent. You can purchase the beneficial insects from specialist retailers. The tiny roundworms are delivered in clay granules (€18.00 at Amazon), which you dissolve in water and apply with a watering can. The best time for combating them is from August, when the fat maggots hide in the ground to overwinter.
Feathered enemies destroy hazelnut borers
Chickens love to eat hazelnut borers and other pests
Hobby gardeners who keep chickens have a clear advantage when it comes to sustainably combating hazelnut borers. Pecking chickens are the declared enemies of beetles and larvae. If you set up a temporary outdoor enclosure around hazelnut trees from March to May, no pest will escape the busy chicken beaks.
The feathered enemies of hazelnut borers and larvae include runner ducks. The cute, flightless ducks are usually hired to fight snails in the garden. Penguin ducks also have beetles of all kinds and their larvae on their menu.
Frequently asked questions
What damage does a hazelnut borer cause?
In June, females drill a tiny hole in the still soft shell of young hazelnuts and lay a single egg. After four to five weeks of development inside the nut, a larva eats its way through the shell. The original, barely noticeable round opening is enlarged to a diameter of up to 2 millimeters. The unmistakable damage caused by an infected hazelnut is this drilling and removal hole.
Can hazelnut borers fly?
Yes, adult hazelnut borers can fly. Like most weevils, hazelnut borers are also equipped with a functional flying apparatus. However, the beetles prefer to walk around on foot in search of hazelnut trees and other fruit trees.
How can you prevent hazelnut borer infestation?
Regular tillage in the area of the tree crown from early spring destroys overwintering larvae before they fly out as finished beetles. Rake the soil of the root disc vigorously. Ideally, you should then cover the tree disc with a weed or garden fleece that catches hatched beetles. Beforehand, we recommend fertilizing with lime nitrogen, which has proven effective in the biological control of all kinds of larvae.
Where can you buy nematodes against hazelnut borers?
There are numerous purchasing sources in specialist retailers and online, such as hardware stores or garden centers. Not all of them take into account the fact that they are living beneficial insects. We therefore recommend purchasing nematodes directly from competent breeding farms. Animal-friendly delivery of the valuable cargo is guaranteed here.
Tip
Deep in the ground, hazelnut borer larvae cannot feel safe when Mr. Mole is there. What chicken beaks and nematodes don't catch is just right for the underground beneficial insect. Fat larvae do not remain hidden from the sensitive mole nose for long in their winter quarters. For this reason, natural gardeners do not prey on the helpful insect eater and generously tolerate the occasional molehill in the bed.
