Spider mites are the worst nightmare for any gardener. In this article, we explain how to recognise an infestation, and the best course of action to fight off a swarm of these pests, all with natural household remedies.
Every hobby gardener who has dealt with spider mites knows how persistent they are. Spider mites are not picky and will infest whatever plant comes their way, be that outside on the wall or the windowsill. Tomatoes (Solanum lycopersicum), cucumbers (Cucumis sativus) and other vegetables cultivated in greenhouses are especially prone to spider mites. If the infestation is on the smaller side, it can go completely unnoticed. In dry and warm or hot weather, however, spider mites reproduce rapidly and become a serious problem.
Identifying spider mites
These small red spiders on their own are small enough on their own that they can be difficult to recognise. Spider mites are well under a millimetre, so unfortunately for our lovely gardens, they only become apparent when plants are heavily affected. You will find small webs on the leaf stalks and branches. With the help of a magnifying glass, you will also be able to detect the individual spiders. Spider mites (Tetranychidae) are tiny arachnids. Their eight legs aren’t always the easiest to count, the rear two pairs being rather inconspicuous. Depending on the species the little spiders can differ in appearance. The colour spectrum of the adult animals ranges from yellow to green and even fiery red. In Europe, the red spider mite (Tetranychus urticae) – also known as two-spotted spider mite – and the European red mite (Panonychus ulmi) are the most common types of spider mites.
In a nutshell, spider mite infestation is most easily identifiable by the webs and spider mite specific damage caused on the plants.
Tip: Try spraying the suspected plant with water using an atomiser, the small droplets of water will stick to the webs making them more visible.
In contrast to aphids, which feed on the plant sap from leaf veins, spider mites draw their sap supply from individual leaf cells, causing blotchy patterns. The fading colour on leaves or flowers spreads continuously as the infestation progresses. It may lead to deformed shoot tips or dehydration of the infested plant parts. The discolouration of the leaves is accompanied by the formation of webs and a large number of small spiders inhabiting the web.
How to get rid of spider mites
Beware to not underestimate the persistence and damage of these devilish pests. Spider mites spread fast, easily infesting a large number of plants. On top of that, they do not only weaken the plant and make it look unattractive, they can also transmit plant viruses. It is therefore essential to detect an infestation as early as possible and immediately take action.
The first step to gain control of an infestation is to isolate the plant as much as possible. That way, you avoid the spider mites from spreading to neighbouring plants.
How to manage spider mite infestation naturally
We highly recommend avoiding the use of synthetic pesticides, especially in your home or garden. Pesticides are harmful to various beneficial and often crucial organisms. Besides, spider mites are resistant to some chemicals. Extensive use of pesticides fosters wider resistance and is therefore counterproductive. Natural remedies are available at the market, but many of them do not have a systemic effect, meaning they require several applications, which again can be harmful to both the environment and the plant. Some pesticides contain active ingredients from the group of pyrethrins, which are of plant origin but can harm other beneficial insects in your garden. Natural products based on pure rapeseed oil are well tolerated by the environment but require thorough and regular treatment. The same goes for preparations based on potassium soap which are eco-friendly but must be applied multiple times for more effectiveness.
Recap: Natural spider mite management
- If possible isolate the infested plant to prevent the spread of the outbreak.
- Pesticides do more harm than good, they can cause damage to the entire ecosystem and will promote the chemical resistance of spider mites.
- Natural preparations based on rapeseed oil or potassium soap are effective but require repeated application.
Household remedies against spider mites
Home remedies for spider mites can only be used to a very limited extent. When treating an outdoor plant, remove severely infested shoot tips or parts of the plant if tolerant to pruning. Since spider mites do not like moisture, a slight infestation can be treated by daily spraying the entire plant with a garden hose or inside the shower. In summer you can also place infested indoor plants outside when it rains.
Another common method is to increase humidity by covering the plant with a plastic bag. Before you try this we urge you to remember that this can sometimes backfire as the stored air underneath will risk damage to the plant. We recommend leaving the plastic bag on the plant for not more than four days. After a two-day break, you can put the bag over the plant again for four days.
Finally, another simple trick is to use a water-oil mixture. Rapeseed oil can work wonders and is quite an inexpensive remedy. To combat the troublesome spider mites, mix 70 millilitres of water with 30 millilitres of oil. Shake well until it forms a white emulsion. Apply to the whole plant, including underneath the leaves. Remember to keep shaking the bottle once in a while so that the components of the mixture do begin to separate. Unfortunately, many plants do not tolerate treatment with rapeseed oil very well, as it dissolves the protective cuticle of the leaves. To reduce the harm apply the rapeseed oil emulsion only in the evening when the sun is less strong. Repeat not more than three times. If this measure does not take effect within a week, resort to using a natural plant protection product.
Summary: Homemade remedies to treat spider mites
- Isolate infested plants if possible
- Remove infected parts of the plant
- Spray the infested plant with water daily
- Cover infested plant with a plastic bag to increase the air humidity
- In summer, place indoor plants outside when it rains
- Apply a spray mixture of 70 % water and 30 % rapeseed oil, treat plants a maximum of three times
This might be surprising, but some beneficial insects can help reduce an infestation of spider mites. Predatory mites such as Phytoseiulus persimilis or gall midges such as Feltiella acarisuga will help to keep the pests under control. It makes sense to use predatory mites mainly in a greenhouse or indoors, where spider mites ultimately cause the most damage. Beneficial insects will not emigrate quickly from an enclosed area. Note that although called “predatory” the little helpers are not dangerous to humans.
Out in the garden or field, it makes sense to create a habitat that predatory mites will naturally populate in. While you are treating a spider mite infestation with beneficial insects, you should not use pesticides as these could harm the useful organisms.
Prevention is most often better than the cure with most of the nuisances that can occur in life. Why would your garden be any different? Focusing on preventative measures is the best way to manage spider mite infestation. Especially outdoors in hot temperatures and dry weather will increase the risk of a spider mite epidemic. Therefore, monitoring those conditions will enhance your chances of winning against the little creatures. Here are our top tips:
- Beneficial insects such as gall midges can help you keep spider mites at bay. Natural flower beds with flowering herbs such as chamomile (Matricaria chamomilla) will attract gall midges and other beneficial insects. You can easily create flower borders or pots with seed mixtures which are full of beneficial flowering plants. Make sure to use gentle plant protection products in general for your garden routine. By saving beneficial insects you will save yourself a lot of work.
- Boost your plants but do not use fertilisers with a high amount of nitrogen. Too much nitrogen will make your plants more susceptible to spider mites. Rather keep an eye out for how much you fertilise and try using plant-based fertilisers.
- In greenhouses, you can avoid heavy infestation by regulating the temperature and humidity. Make sure that air humidity is not too low, and the temperature is not too high. Spider mites thrive in dry conditions with temperatures at around 30 °C.
- During winter spider mites can even become indoor pests due to the dry and warm conditions. Be particularly careful when bringing potted plants into the house for the cold season. Carefully examine the plants for spider mites and other pests.