03/04/2025
Plant protection without chemicals: What helps against pests?
Whether in your own garden or on the supermarket shelves: residues of chemical pesticides accompany us - often unnoticed - all the way to our plates. But there are effective alternatives - even for the home garden. Dr Hermann Kruse, environmental toxicologist at Kiel University, shows how natural plant protection works, which methods really help and why fewer chemicals mean better health - for humans, animals and the environment.
When pesticides end up on your plate - Why healthy eating starts with cultivation
Chemical pesticides are an integral part of conventional agriculture. Around 300 different active ingredients are authorised in our country. Some of them are suspected of being endocrine disruptors or even carcinogenic. Even if legal maximum quantities are adhered to, this can pose a health risk for sensitive groups such as children or people with pre-existing conditions. Dr Kruse therefore emphasises that the fewer chemical residues that end up in our food, the better it is for our health.
How contaminated are fruit and vegetables?
Although the residues in most foods are below the official limits, this does not automatically mean the all-clear. In a study, pesticide residues were found in many samples from conventional cultivation - including some that are no longer authorised in the EU. White wine (89.4%), pineapple (88.6%) and strawberries (88.0%) were the most frequently contaminated. The figures for fruit and vegetable products for infants and young children are particularly alarming: almost one in ten samples exceeded the permitted limits and should therefore not be sold at all. Organic products fare much better; here, exceeding the limits is the exception. Particularly strict standards apply to Demeter products.
When limit values reach their limits
Limit values for pesticide residues are intended to provide safety - but their significance is limited because they are not based solely on toxicological criteria, but also take into account the importance of an active substance for agriculture, for example. In the case of a pesticide that is considered very important for agricultural practice, the limit value can therefore be somewhat more generous. In addition, for substances without a specific maximum value, a general maximum value of 0.01 mg/kg applies - regardless of their hazardousness. Therefore, health risks cannot be ruled out in individual cases even if the limit values are adhered to. One example of this is glyphosate, which is still authorised in the EU until at least the end of 2033 despite indications of possible embryonic malformations and cancer risks.Protecting plants without chemicals - prevention instead of pesticides
If you want to protect your plants in your home garden naturally and effectively, you should start early - even before pests appear. Healthy soil and robust plants are the most important basis for successful plant protection without chemicals.
Proven measures include:
- Choose resistant plant species: When selecting plants, choose varieties that are naturally more resistant to fungal infestation and other pests.
- Healthy plants through humus and compost: A healthy soil, for example through targeted humus build-up and the use of compost, promotes the vitality and resistance of plants.
- Mechanical weed control: Regular hoeing helps to keep weeds in check.
- Crop rotation: Regularly alternating between green plants and stalk plants naturally reduces unwanted weeds.
- Maintain green strips and hedges: Natural hedges and grass verges provide a valuable habitat for beneficial insects and birds.
- Hang up nesting boxes: Nesting boxes attract songbirds that feed on butterfly caterpillars and other insect pests.
- Insect hotels: They provide a habitat for insects that are known as antagonists to aphids, spider mites, etc. Important: Always protect the entrance to the insect hotel with a wire mesh so that the beneficial insects do not fall victim to a hungry woodpecker.
Naturally against pests - biological plant protection as an alternative
- A single ladybird destroys up to 3,000 aphids in its lifetime.
- Ichneumon wasps help reliably against food moths. They lay their own eggs in the moths' eggs, destroy them and automatically disappear once the moths have been eliminated.
- Predatory mites are an effective remedy against spider mites in apple orchards.
- Nematodes, microscopically small threadworms that are adapted to the respective pests, effectively combat the larvae of the weevil, fungus gnat, meadow snake (Tipula), codling moth and cockchafer, as well as slugs and snails. However, nematodes are currently still quite expensive.
- A hedgehog- and lizard-friendly environment has proven effective against snails. Hedgehogs like to eat slugs and snails, while lizards prefer slugs and snails.
- Collecting potato beetles by hand is labour-intensive but highly effective.
- Oak processionary moths can be easily vacuumed up (with appropriate protective clothing).
- Regular hoeing or weeding keeps weeds at bay in the long term.
- Yellow glue traps reduce the infestation of cherry fruit flies.
- Light traps attract nocturnal pests such as moths and keep them away from crops.
- Cleverly chosen acoustic signals can also act as a deterrent. One successful example is recordings of scolding starlings in cherry trees, which - unlike rattling noises or gunshots - really help.
- Simple heating without any chemicals helps against house longhorn beetles, a type of beetle that damages the wood in roof trusses and timber-framed houses. Short-term heating (e.g. in a sauna) or freezing at very low temperatures is also effective against bedbugs and house dust mites.
- Wood can be well protected against fungal infestation by careful drying. Mould has no chance if the moisture content is below 18 percent.
- Hulls can be protected from mussels and algae with a weak current that alternates between plus and minus.
- Slurry: With the right herbs and water, you can easily make slurry to ward off unwanted guests in the garden: Examples include clary sage and lavender against various pests, elderberry against voles (undiluted) or cabbage whitefly caterpillars (diluted 1:5 for spraying) and bracken against slugs.
- Lavender can also be used as a tea or as a distraction plant to protect against pests.
- Tagetes (marigold) as an interplanting protects against nematodes, which damage the roots of crops, and attracts slugs. This increases the chance that lettuce and other crops in the neighbourhood will be spared.
- Tansy as an interplanting keeps potato beetles and caterpillars away.
- Leeks between other plants reduce fungal infestation.
- Onions act as a deterrent to various pests when planted between crops.
- Black aphids love nasturtiums. Nasturtiums are therefore an excellent deterrent plant. It can also be used as a tea.
Active ingredients from nature - from neem extract to pheromones
In addition to beneficial organisms and mechanical measures, nature offers plant-based and biological active ingredients that have a very specific effect and are much less harmful to the environment than chemical pesticides.
- Neem extract: The extract from the Indian neem tree effectively protects plants from pests such as the Colorado potato beetle and phylloxera. Neem not only acts as a feeding poison, but also as a deterrent - and is harmless to bees.
- Chrysanthemum extract (pyrethrin): This plant-based active ingredient reliably combats aphids, whiteflies and spider mites. Unlike synthetic pyrethroids, natural pyrethrin breaks down quickly and has no long-term impact on the environment.
- Bacterial preparations: Bacillus thuringiensis (Bt) is used to protect against feeding pest caterpillars. It is particularly effective against the box tree moth, but also the oak processionary moth.
- Viruses: Products containing the granulosis virus are a good remedy against codling moth larvae.
- Fungi: The fungus Beauveria bassiana can be used against the bark beetle, the related fungus Beauveria brongiartii against cockchafer.
- Pheromones: These natural scents or messenger substances are used by insects to communicate and can be used specifically to attract or repel pests such as the bark beetle or the grape berry moth, which is feared in viticulture. Pheromones can also be used to control cherry fruit flies and aphids without any risk to other organisms.
Advantages and challenges
When used correctly, biological plant protection offers effective alternatives to chemical agents. Depending on the method, a certain amount of planning and patience is required, as:
- Beneficial organisms can usually only be stored for 1-3 days at 8-12 °C.
- Beneficial organisms can usually only be applied from March to October under certain conditions.
- The use of beneficial insects is usually more labour-intensive and time-consuming than chemical measures.
- Regular checks are essential.
- Biological measures often work more slowly than chemicals.
The most important point of criticism from the point of view of agriculture is the higher cost of biological preparations compared to chemical agents.
On the other hand, however, there are decisive advantages:
- Low risk of pests developing resistance.
- Targeted effect that protects other living organisms and beneficial organisms.
- Particularly important for farmers: no certificate of competence is required - so even temporary staff can carry out the measures. In addition, there are no restrictive requirements for groundwater, water or bee protection, no re-entry periods and no waiting periods after application.
- For consumers, the biggest advantage is the sustainable protection of their own health and the environment: the fewer chemical agents are used, the lower the impact on humans, animals and ecosystems.
Conclusion: Less chemicals, more health
Organic plant protection is not just an alternative, but a real benefit - for our health, our environment and the quality of our food. Many methods have already proved successful, even if they are still somewhat more expensive than the health-threatening chemicals. However, they save on the rising health costs that are now visible everywhere! - And the more frequently and consistently biological plant protection is used, the better and more cost-effective it will be in the future.
Dr Hermann Kruse sees biological methods as a forward-looking solution: "The more consciously we avoid pesticides and promote natural alternatives, the more we protect the environment, soil and drinking water - and not least our own health.
His clear appeal is that anyone who favours organic plant protection is acting in a forward-looking, sustainable and responsible manner - for themselves and for future generations.
Our tip for anyone interested in natural plant protection
The article (in German only) is based on a lecture given by Dr Kruse at the 24th Lübeck hoT workshop. You can find the full lecture and subsequent discussion on the VBN-Verlag YouTube channel.