If a brown-beige butterfly flutters around the garden at the first frost, hobby gardeners are not happy. This late in the year it can only be the frost moth that will cause the trees to be bare by the next spring. You can find out here what a frost moth is, how it lives and what damage it causes. How to combat the pest with natural remedies.
How can frost moths be controlled naturally?
Frost moths are butterflies whose caterpillars can eat bare trees in spring. To combat them, natural means such as glue rings, caterpillar glue, parasitic wasp settlement, predator attraction or an organic plant protection product with neem can be used.
- Frost moths are butterflies whose caterpillars can eat entire trees bare in spring.
- Flying males are beige brown to ocher yellow with a wingspan of 20-46 mm. Flightless females are 5-14 mm long, brownish-grey in color with short wing stubs.
- Venuous caterpillars are 25-40 mm long, green or rusty brown with stripes that move in a cat-humping manner.
What is a frost moth? – Briefly explained
Frost moth is a butterfly and a feared pest on fruit trees as well as wild and ornamental trees. In spring, the caterpillars feed on leaves, flower buds, young shoots and fruits. If the infestation is severe, baldness occurs. Often only leaf veins, remains of droppings and inedible fruits remain on the affected tree.
Frost worm profile
In Germany the frost moth is represented by two species. Small frost moth and large frost moth differ in size and color. This applies equally to butterflies and caterpillars. A pronounced difference between sexually mature males and females (sexual dimophism) is characteristic of both species. The following profile has the details:
| Profile | Small frost moth | Large frost moth |
|---|---|---|
| color | beige brown to grey-yellow speckled | ochre yellow, black patterned |
| Body length | 5-7mm | 10-14 mm |
| Male Wings | 20-25 mm span | 40-46 mm wingspan |
| Female Wings | Stub (flightless) | Stub (flightless) |
| Caterpillar Color | greenish with stripes | yellowish-red-brown with stripes |
| Caterpillar length | 20-25 mm | 35-40mm |
| Special feature | pushing, humping locomotion | pushing, humping locomotion |
| Egg Size/Shape | 0, 3-0, 4 mm small, oval | 0, 4-0, 5 mm small, oval |
| Egg Color | pale green, later orange-red | pale yellow, later orange-red |
| Status | Fruit tree pest | Forest pest |
| Botanical name | Operophtera brumata | Erannis defoliaria |
Small frost moth causes significantly greater damage than large frost moth. Both species are dangerous for a tree. Please read the following sections for more detailed explanations of the appearance, lifestyle and damage pattern in order to recognize an infestation in good time and take effective countermeasures.
Appearance of butterfly and caterpillar (lesser frost moth)
The small frost moth only grows up to 0.7cm
The forewings of the male butterfly are rounded, gray-brown to beige-brown with dark, wavy transverse lines. Yellowish fringes along the edges of the wings are noticeable. In contrast, the hindwings are pale yellow in color. In the flightless female, only short, brown wing stubs with gray-yellow mottling can be seen. The mouthparts are atrophied because a frostbite butterfly does not eat during its short lifespan.
The voracious caterpillar is light green with three light longitudinal stripes and a dark central stripe on the back. Typical for the peeping tom larva is a cat's hump when moving.
Appearance of butterfly and caterpillar (great frost moth)
With pale ocher-yellow, black-patterned and rust-brown-lined forewings, a male frostbitten moth flutters around in the twilight. The wingless, yellowish-brown, black spotted female looks more like a beetle.
Caterpillars can be admired in different color variations. A reddish-brown back with yellowish side stripes is just as common as a black-brown color with light spots and other varieties.
Excursus
Frost moth caterpillar surprises with clever gliding
The frost moth caterpillar is an amazing climber
Missing wings and humped locomotion do not prevent a frost moth caterpillar from flying high. In fact, every year high-rise balcony gardeners rub their eyes in amazement at frostbite infestations on their container plants at lofty heights. The butterfly caterpillars copied their stroke of genius from young spiders in Indian summer. If an apple tree is crowded, the newly hatched larva spins a long thread and drifts with the wind to new pastures with juicy leaves.
Destructive lifestyle
The name frost moth refers to a rather unusual mating season in late autumn after the first frost. A development is taking place that could destroy all hopes of a rich harvest on pome fruit trees next spring. In home and allotment gardens, apple trees, sweet cherries and plums are primarily affected by the small frost moth. The large frost moth sets its sights on maple, oak, beech and hornbeam hedges, which it leaves behind as bare skeletons. The following overview will give you a quick look at the fatal way of life:
- Mid/end of October, the butterflies emerge from the pupae in the ground and the flight period for males begins
- Mated females climb up the tree trunk or wait for a male visit in the crown
- Egg laying in bark depressions or winter buds
- Overwintering the frost-hardy eggs in a dormant state
- The caterpillars hatch parallel to budding and the beginning of the flowering period
- Maturation feeding by the larvae on leaves, shoots and buds
To protect themselves from predators, frost moth caterpillars weave a small nest made of fine threads between the leaves. From June, at the end of development, the adult larvae descend into the ground to pupate. The picture below illustrates the timeline of development:
malicious image
Caterpillars of both species of frost moth feed on buds and young leaves. As early as May, the first damage and cat-humping green or reddish-brown larvae can be seen in the treetops. As the process progresses, nest-like webs form between the leaves. What's bad to look at are eaten tufts of leaves stuck together by spider threads. The damage threshold on the way to clearing is 4 caterpillars per 100 flower or leaf clusters. It starts with pitting and ends with sad leaf skeletons.
If caterpillars are still present in the fruit tree at the time of fruit formation, they attack apples, cherries and plums. A typical damage pattern is so-called spoon-feeding, which occurs on one side of a fruit that falls off prematurely or is corked in an unappetizing manner.
Fighting frostbite naturally – overview
Glue rings protect trees from frostbite infestation
Avoiding chemical insecticides in the natural garden does not mean that you are defenseless against frost moth infestation. In fact, you can effectively combat the pests using natural remedies. The following table provides an overview:
| Combat | Medium | Application | When? |
|---|---|---|---|
| Mechanical | glue ring | lay around the tree trunk | September to May |
| Home remedies | Caterpillar glue | paint on trunk bark | September to April |
| Natural enemies | Parasitic wasps | settling outside in spring | from 15° Celsius |
| Predators | Birds, chickens | attract, let run free | in spring |
| Plant protection products | Neem as a spray | Spray tree | 10 days before flowering begins |
The correct application procedure is explained in more detail in the following sections:
Glue ring protects apple tree – this is how it works
The glue ring is a band made of paper or plastic, coated with a tough adhesive that does not dry. Properly attached, a glue ring prevents female frost moths from crawling up the trunk and laying their eggs. How to use the control agent:
- Best time is the end of September
- Select as smooth a spot as possible at a height of 50 cm on the trunk
- Cut the glue ring (trunk diameter plus 3-5 cm overlap)
- Place strips with the non-glued side around the tree trunk
- Remove the protective film, stick it on and press it on
- Fix additionally with covered wire at the top and bottom
- Important: Remove the glue ring in May at the latest when the trunk begins to grow thicker
If there is a support post on the side of the tree, attach a glue ring to it as well. Regularly remove clinging leaves that cunning female frost moths use as a bridge. Please take this opportunity to check that it is firmly seated so that you can replace the glue ring if necessary.
You can find out how a glue ring works as a natural protection against frost moths on apple trees in the following video:
Leimringe gegen Frostspanner
Make and apply caterpillar glue yourself
Caterpillar glue has proven to be a good home remedy for frostbite in the home garden. If the adhesive is applied directly to the bark, it is guaranteed that no loopholes can form under which females lay their eggs. Furthermore, caterpillar glue can remain on the tree all year round because no fastening material can constrict the trunk. The following recipe is suitable for making caterpillar glue for 10 trees:
- Heat 700 g of wood tar and 500 g of tree resin (rosin) in a water bath while stirring constantly
- Stir in 300 g fish oil or vegetable oil
- Stir the mixture until it has cooled
- Use at the end of September/beginning of October
- Apply caterpillar glue at a height of 50-80 cm as a 20 cm wide and 2 mm thick ring
Dose the fish or vegetable oil when making it so that a tough, sticky mass is created that does not drip.
Settling parasitic wasps
Parasitic wasps should be provided with living space so that they stay long-term and keep frost moths away
Natural enemies of the frost moth are parasitic wasps, spiders and ground beetles, which like to find themselves in natural gardens. If the number of pests becomes excessive, the population of beneficial insects is not sufficient to stop the voracious caterpillars. Smart hobby gardeners settle additional parasitic wasps in the garden because the delicate insects achieve considerable success in combating them. Parasitic wasps parasitize frost moth caterpillars, which die within a short time. The hard-working little helpers are bred in special farms that deliver the squadron to your home.
- Order parasitic wasps in spring when outside temperatures exceed 15° Celsius
- On the day of delivery, hang tubes with live parasitic wasp larvae in the plant
- Let the tube hang for at least 10 days so that all beneficial insects hatch and fly out
Offer the helpful insects living space in the garden so that they don't wander off again after their work is done. A thick branch with small holes serves as a parasitic wasp hotel. Wildflowers and mixed flower hedges invite parasitic wasps to feast on nectar and linger.
Tip
Parasitic wasps are masters of multi-tasking. First, all frost moth caterpillars and codling moth larvae are parasitized. The beneficial insects then turn to other pests in the garden. The genus Aphidius colemani prefers to target aphids. A single parasitic wasp kills up to 200 lice in her short life.
Predators versus frost moths
For birds, the late flight and mating season of frostbitten moths is a welcome opportunity to fill their bellies before the harsh winter. Flying males and crawling females spice up the meager diet of numerous garden birds. If there are chickens pecking in the garden, the hatched butterflies have a bad chance when they crawl out of the ground.
Use organic plant protection product Neem correctly
Neem does not kill the caterpillars, but prevents them from breeding
The Indian neem tree (Azadirachta indica) serves as a global role model in the production of plants' own defense substances. Its main ingredient, azadirachtin, provides excellent services as a biological plant protection agent against frostbite, aphids, boxwood borers, lily beetles and the dreaded Colorado potato beetle larvae. However, there is no effect against codling moth.
The active ingredient in neem is distributed as a spray over the entire plant. A frostbite caterpillar absorbs the agent through its body and food. Within a few days, azadirachtin interrupts the development of the larva and stops feeding. No pupation takes place and the vicious circle of reproduction is stopped. This is what you need to pay attention to when using:
- No immediate effect: Apply the product in good time, ideally 10 to 14 days before the flowering period begins
- Complete wetting: Spray the tree all over, especially the top and bottom of the leaves
- Observe temperature: Use neem remedies at temperatures below 25° C
- Overcast weather: Only apply organic products in direct sunlight
Organic plant protection products with neem achieve maximum control success when the early stage of a frost moth caterpillar is affected. The impact power against an adult butterfly is only small. The product is available from specialist retailers under various trade names, such as organic pest-free neem from Bayer, Naturen organic pest-free neem or insect-free neem from Compo.
Frequently asked questions
It is not possible to attach a glue ring to our apple tree because the bark is particularly cracked. What to do?
We recommend coating the trunk with caterpillar glue to protect against female frostbite moths. You can make the glue yourself or buy it ready-made. A tried and tested product is caterpillar glue green (€23.00 on Amazon) from Schacht. Apply the glue as a 20 centimeter wide and 2 millimeter thick ring at a trunk height of around 50 centimeters.
Are frost moths always harmful to a tree?
No. Serious damage to trees only occurs when there are numerous infestations. In fruit growing, the damage threshold is when there are 3 to 4 caterpillars on the tree for every 100 leaf or flower clusters. On plum and apple trees, the damage threshold increases to 10 to 15 caterpillars. A lower number of caterpillars also causes leaf loss, which a he althy tree can cope with without any problems.
What damage do frost moths cause on apple trees?
In spring, the caterpillars eat the pistils and stamens of flowers, which then cannot develop. The leaves are partially glued together and spun into a nest. Initial pitting worsens over time to pitting down to the leaf veins. Young apple fruits are also damaged because the caterpillars eat the pulp.
Tip
Biological pest control takes time to be fully effective. What to do when it's too late for glue rings, natural enemies or neem sprays? Under these circumstances, hobby gardeners who are close to nature turn to a biocide based on the bacterium Bacillus thuringiensis. The spray is non-chemical, gentle on beneficial insects and destroys frost moth caterpillars within a few days.
