Spider mites: Proven tips to protect your crop

Spider mites are one of the most dangerous pests a grower can encounter. These tiny, almost invisible arachnids can cause enormous damage and, if you don't stop them, can destroy an entire crop within weeks. In this article we will look at how to recognize spider mites, why they thrive on your plants and how to tackle them effectively.

What are spider mites and why are they so dangerous?

Spider mites are small arachnids from the Tetranychidae family, whose most common representative in indoor grow rooms and gardens is the two‑spotted spider mite (Tetranychus urticae). These microscopic pests reach only about 0.4 mm, have four pairs of legs and vary in color depending on species and environment – from green and yellow to red.

Spider mites reproduce incredibly quickly and under ideal conditions (heat, dryness) can literally cover an entire plant within a few weeks. Besides their rapid reproduction, spider mites are tricky because they easily hide in the folds between leaves. Females create shelters in the plant tops or between leaves where they lay eggs. The eggs hatch into larvae after 3–15 days, which mature over the next few days and continue the colonization. At high temperatures and low humidity this cycle speeds up dramatically. That is why spider mites are a common problem especially in enclosed indoor spaces or greenhouses.

How to tell if you're dealing with spider mites

Spotting spider mites on plants is difficult, as they are often invisible to the naked eye. What you should not overlook, however, are the warning signs that accompany a spider mite infestation:

• Small yellow‑white speckles on the leaves, mainly on the underside where spider mites prefer to suck sap.
• Fine webbing between leaves, on stems and at the plant tops. A typical sign of heavy spider mite infestation.
• Wilting and premature leaf drying, even when the plants have enough water.

Natural methods to fight spider mites

If you have noticed spider mites on your plants, try proven natural methods before reaching for chemicals. They are gentle on the environment and often very effective:

• Adjusting the climate: Spider mites like heat and dryness. If you cultivate indoors, lower the temperature below 25 °C and increase relative humidity to 60–70 %, which will slow their reproduction. Better air circulation also helps by making it harder for the pests to move around the plants.
• Mechanical cleaning: Spider mites can be removed mechanically from leaves, most easily with a damp cloth or a vacuum set to low power. If possible, try showering the plants.
• Biological control: Predatory mites such as persimilis, californicus, A. andersonii, N. fallacis and G. occidentalis are also effective against spider mites, as well as the predatory midge Feltiella acarisuga, and predators like Stethorus punctillium and Oius insidiosus.

Products against spider mites

In cases of heavy spider mite infestation it is necessary to use sprays – even here you can choose between gentler and more radical solutions.

Natural sprays and soaps against spider mites

These products are gentle on the environment and, besides spider mites, also protect plants from pathogens and other insects. Proven natural products against spider mites include:

• Neem oil: Biocont NeemAzal
• Oil emulsions: Rock Effect
• Biological sprays: BioBizz Leaf Coat, Canna Cure, NATURA, BHB MM, Spider Plant

Chemical sprays against spider mites – acaricides

Products intended specifically for sap‑sucking pests like spider mites are called acaricides. Exercise caution when using them on plants intended for consumption. These products require safety intervals and can be harmful to your health.

• Biocont PREV-GUARD
• AgroBio Karate
• SmC Spidermite Control
• Agro Sviluška STOP
• Spruzit Pest Free
• Nissorun

You might be interested in: How to get rid of slugs

For more advice on fighting pests and other tips and tricks for indoor and outdoor growers visit our Higarden blog.