How to Identify and Control Common Bergenia Pests

Is this a familiar scenario? You get up after a good night’s sleep and check your garden. It looks like there are notches on your bergenia leaves that weren’t there yesterday. Could that be…?

While bergenia is generally resistant to pests, there are two exceptions: weevils, especially black vine weevils, and gastropods.

A close up vertical image of bright pink bergenia flowers growing in a sunny garden. To the center and bottom of the frame is green and white printed text.

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Black vine weevils emerge at night and feed on the outside of the leaves, resulting in a notched appearance around the edges.

Slugs and snails are also nocturnal creatures that can cause damage.

In this article, we will cover what you what to look for and how to protect your bergenia plants from these pests.

Black Vine Weevils

It figures that, out of a genus of more than 1,500 species of weevils, the one that feeds on bergenia (Otiorhynchus sulcatus) is known for being the most destructive.

A close up horizontal image of a black weevil feeding on a leaf pictured on a black background.

This type of weevil also favors rhododendrons, camellias, primroses, and euonymus, and it may opt to feast on almost 100 other kinds of plants as well!

These insects are native to Europe, but they have had no problem colonizing the US and southern Canada.

Symptoms

Your first clue that these pests are active in your garden is typically going to be visible notches on your bergenia leaves.

A close up vertical image of bergenia foliage showing the damage done by chewing insects.
Photo via Alamy.

Most gardeners like to trim back the damaged foliage in the spring.

While this damage is often minor, the populations of these insects can build up over time.

Particularly true since the weevils cannot fly, they typically stay in the same place and reproduce. (Asexually!)

Bergenia’s leaves are evergreen, so any damage to them becomes magnified as infestations increase.

Although the notches on the leaves are the most easily observable symptom, the larvae that feed on the roots can also damage the plants.

This usually manifests as a general decline in plant health, and is more difficult to diagnose.

If you examine the soil around infested plants in the spring or fall, you will find larvae that are about half an inch long, golden colored, and shaped like a C.

A close up vertical image of the C-shaped larvae of a black weevil, pictured on the surface of the soil.

Though this is usually not a problem with bergenia, severe infestations can completely destroy the roots, and ultimately kill the plants.

How to Control the Adults

The adult weevils, all of which are female, hide in the soil or debris at the base of the plants during the day, and come out at night to feed on the leaves.

A close up horizontal image of a snout-nosed weevil on the leaf of a plant pictured on a soft focus background.

You can find them after dark just by shining a flashlight on your plants.

The 3/8-inch-long black weevils have pronounced snouts and black bodies. This makes it easy to find them, so you can pluck them off the plants and put them in a bucket of soapy water.

Another way to catch them is to place a pizza box or some other kind of corrugated cardboard around the plants that are infested. Leave it overnight, then just throw the cardboard with the weevils out in the morning.

If your plants are inundated with these weevils, there are several biological and chemical controls that you can use.

You have several options to kill the adult black vine weevils by using organic treatments as well. 

Mycoinsecticides

In case you are not familiar with the term mycoinsecticide, it is used to describe fungi that control insects. Myco is Greek for fungus, and you know the rest.

A close up vertical image of a plastic bottle of BotaniGard ES insecticide isolated on a white background.

BotaniGard ES

The primary insecticidal fungus used commercially is Beauveria bassiana, which is available from Arbico Organics as BotanicGard® ES, along with other formulations.

The fungus comes in a solution that you can spray on your plants weekly.

Pyrethrins

These chemicals are derived from chrysanthemums, and many formulations of them are labeled as organic.

You will have to apply them more frequently, because they don’t persist on the plants as effectively as conventional chemical insecticides.

A close up square image of three different sized bottles of PyGanic Gardening Insecticide isolated on a white background.

PyGanic Gardening

PyGanic Gardening, available from Arbico Organics, is effective against weevils.

Follow the instructions on the label to dilute the solution, and spray it on affected plants.

How to Control the Larvae

These weevils overwinter as partially developed larvae in the ground and feed on roots – the fine ones in the fall, and larger roots in the spring.

They can be a particular problem in container plantings, since the growth of the roots is restricted.

However, this time spent underground provides a golden opportunity for the gardener to control them with beneficial nematodes.

Beneficial Nematodes

You can find these organisms in some garden centers or online from Arbico Organics, which sells NemaSeek™ SK Beneficial Nematodes.

A close up square image of the packaging of NemaSeek SK beneficial nematodes isolated on a white background.

NemaSeek SK Beneficial Nematodes

This product is composed of Steinernema kraussei, a species of nematode that is particularly effective at cooler temperatures.

Treat the plants in early fall, before the grubs become too large.

Add the nematodes to water as indicated in the directions, and then pour over the soil. The nematodes will seek out and kill the grubs.

This treatment will be the most effective if the soil is moist at the time of application, and then kept that way for four to five days.

You can learn more about how to use beneficial nematodes in our guide.

Insecticides

You can also apply a systemic insecticide, such as imidacloprid, to kill the larvae.

You can buy this compound from the Home Depot in the form of Bonide Systemic Insect Control Granules.

A close up square image of the packaging of Bonide Systemic Granules Insect Control showing a plastic bottle on the left of the frame and text to the right.

Bonide Systemic Insect Control Granules

Follow the instructions on the label, and add the granules to the soil. Then dig them into the surface of the soil, and add water to move the insecticide into the soil.

The roots will absorb the chemical, and transport it throughout the plant. When the larvae feed on the plants, they will ingest the imidacloprid.

Reapply every eight weeks.

Slugs and Snails

If you thought the black vine weevil larvae were slimy, things are about to get even slimier with the dreaded slugs and snails that may be paying a visit to your garden.

A close up horizontal image of a slug moving around the garden looking for food.

While slugs and snails don’t tend to mow bergenia to the ground like they do with so many other plants, they can cause occasional problems for these beauties.

Damage is most likely to occur on older leaves. Watch for jagged holes in the leaves and trails of slime.

Removing any decaying foliage will greatly limit the appeal of the plants to slugs and snails, while improving the look of plants for human visitors to your garden.

If your bergenia is plagued by one or both of these slime-mongers, we have a whole guide devoted to banishing slugs and snails.

In this case, you can prevent an infestation by removing the older leaves in the spring. If you do have slugs or snails in your bergenia plants, you can hand pick them or apply diatomaceous earth around the plants.

Bergenia Plants Are Highly Resistant to Most Pests

Now that I’ve gone through all of the common worst case pest scenarios that can happen with bergenia, it is a good time to reiterate that these plants are usually safe from insects and larger herbivores, like rabbits or deer.

A close up horizontal image of the bright pink flowers of a bergenia plant growing in the garden pictured in bright sunshine.

Even if your plants are infested with black vine weevils, it can take years for the populations to build up to the point where they cause severe damage.

And you can easily avoid slugs and snails with routine garden cleanup.

All in all, bergenia really is a low maintenance plant that is resistant to most pests.

Have you managed a black vine weevil or slug infestation in your bergenia plants? Or have yours been pest free so far? Let us know in the comments section below!

And for more information on growing bergenia in your garden, check out these guides next:

About Helga George, PhD

One of Helga George’s greatest childhood joys was reading about rare and greenhouse plants that would not grow in Delaware. Now that she lives near Santa Barbara, California, she is delighted that many of these grow right outside! Fascinated by the childhood discovery that plants make chemicals to defend themselves, Helga embarked on further academic study and obtained two degrees, studying plant diseases as a plant pathology major. She holds a BS in agriculture from Cornell University, and an MS from the University of Massachusetts Amherst. Helga then returned to Cornell to obtain a PhD, studying one of the model systems of plant defense. She transitioned to full-time writing in 2009.

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