The red spider mite, scientifically known as Tetranychus urticae, is one of the most common plant mites. With the arrival of warm weather, it promptly appears in our gardens, causing serious damage to various crops. It is a tiny mite that positions itself on the lower side of the leaves. To recognize it, careful observation is necessary. If you notice abnormal, tiny, red dots moving on your plants, it is most likely the red spider mite.
In this article, we will teach you how to identify its presence. Timely action to counter it is of fundamental importance to avoid the harmful effects this mite can cause. There are several biological defenses to counter its infestations without using pesticides, and some of them are straightforward to implement.
So let’s find out together what these defenses are and how to prevent red spider mite infestations.
Identification of Red Spider Mite
The red spider mite is an insect belonging to the family of Acari. It is a mite of very small dimensions, clearly visible only under an electron microscope. Adult females, from spring and summer generations, have an oval shape and a size of about 500 microns. The color is initially pinkish-yellow, then greenish, and finally red, with microscopic brown spots on the sides of the body. Males are even smaller, around 300 microns, more elongated, and mostly red in color. With the naked eye, what we see are very tiny red dots, stationary or moving, on the lower side of the leaves. When the red spider mite is dead, the dots seen are black and immobile.
The red spider mite is a phytophagous mite, meaning it feeds on plant sap. It is also polyphagous, attacking an indefinite number of plant species, both herbaceous and shrubby. Regarding the scope of our discussion, the vegetable plant species most at risk are: beans, zucchini, cucumber, pumpkin, watermelon, tomatoes, eggplants, and peppers. The polyphagous action of the red spider mite consists first of feeding on the plants, particularly on the cytoplasm.
Secondly, this mite weaves a very dense and thin web, which suffocates the plants. The resulting damage includes initial leaf yellowing, severe vegetative desiccation, and ultimately, if the attack is extensive, the death of the cultivation. The damage to fruits is also severe, causing them to harden and become very bitter, rendering them inedible.
The red spider mite has a very rapid biological cycle. Under favorable conditions (greenhouses or warm climate), it can complete up to 8-10 generations per year. Adult females of the last generation, with the onset of the first cold weather, take refuge in dry plant residues, where they overwinter. In spring, they ascend from their winter hideouts, disperse on host plants, and begin their egg-laying activity. An adult female produces between 10 and 20 eggs per day, laying a total of 90-120 eggs during her lifetime. The eggs are not visible to the naked eye and are deposited in the dense web covering the vegetation. While, the larvae become adult mites, going through two nymphal stages.
The best period of development, and thus the damage, occurs in the presence of high temperatures, above 30-35 °C, and low humidity levels, meaning the absence of rain. In these conditions, a cycle can be completed in just 8-10 days.
Biological Defense with Water
Given the characteristics of its biological cycle, the red spider mite becomes noticeable on our crops at the beginning of the hottest period. It usually appears between late May and early June and persists throughout the summer until the arrival of rain. Precisely this characteristic, its preference for torrid heat and low humidity, leads us to talk about the first biological defense technique against this formidable pest, namely water. Yes, we are talking about pure and simple fresh water.
The red spider mite cannot tolerate water and humidity in general. These elements disrupt its rapid reproductive cycle, destroying the eggs. Therefore, if we are in a lucky season with frequent rain showers in open fields, they can naturally reduce the presence of the parasite. Unfortunately, in the summer months, rain is less frequent, so to protect the plants, we need to take action with abundant artificial watering.
Using a classic shoulder pump (available online at this link) filled with preferably cold water (ice can be put into the pump container), it is possible to thoroughly and uniformly wet the vegetation affected by the red spider mite. However, be careful to spray the lower side of the leaves well, where the mite hides and weaves its web.
With this simple, inexpensive, and natural remedy, we can effectively counter the development of the pest. Another recommendation is to carry out watering in the cool evening hours. This is important both to avoid subjecting our plants to excessive temperature stress and to make the action of water more effective and prolonged, creating a situation of higher humidity.
As a preventive measure, we can act with macerates, particularly those of nettle and garlic. In this way, we can discourage the red spider mite from attacking our organic crops.
Another biological technique to counter the red spider mite is to introduce some natural predator insects into the ecosystem. In particular, the use of the phytoseiid mite called Phytoseiulus persimilis has proven to be very effective, and it does not have negative effects on our crops. Other effective phytoseiid mites in this type of fight belong to the Amblyseius and Neoseius genera.
The action of a particular species of ladybug, Stethorus punctillum, of which we have spoken in a previous article, is also very effective.
For an even more decisive action against the red spider mite, it is possible to use sulfur powder alone or in conjunction with other remedies. Sulfur effectively repels the mite, and it is sufficient to spray it in the evening hours with a special sulfur sprayer (available here).
This remedy is particularly useful since, in addition to keeping the red spider mite at bay, sulfur powder is an effective remedy against powdery mildew. However, the downside is that its continuous use, especially if close in time, can cause leaf burn.
- MDPI: “Transcriptomic Responses of Salvia hispanica to the Infestation of Red Spider Mites (Tetranychus neocaledonicus)” – Salvia hispanica, commonly known as chia, is a nutritious food source known for its high omega-3 fatty acid content. This study examines the impact of Red spider mites on the production of S. hispanica.
- MDPI: “Acaricidal Activity and Field Efficacy Analysis of the Potential Biocontrol Agent Bacillus vallismortis NBIF-001 against Spider Mites” – The research evaluates the acaricidal activity of Bacillus vallismortis NBIF-001, which has shown promise in controlling spider mites.
- MDPI: “Evaluation of Resistance of Eleven Maize Races (Zea mays L.) to the Red Spider Mite (Tetranychus merganser, Boudreaux)” – The study assesses the resistance of various maize races to the red spider mite, Tetranychus merganser.
- MDPI: “Acaricidal and Antioxidant Activities of Anise Oil (Pimpinella anisum) and the Oil’s Effect on Protease and Acetylcholinesterase in the Two-Spotted Spider Mite (Tetranychus urticae Koch)” – The study explores the potential of anise oil as a bioacaricide against the two-spotted spider mite.
- MDPI: “The Fungus Metarhizium sp. BCC 4849 Is an Effective and Safe Mycoinsecticide for the Management of Spider Mites and Other Insect Pests” – The research evaluates the efficacy of the fungus Metarhizium sp. BCC 4849 as a mycoinsecticide against spider mites.
- MDPI: “Effects of Clonostachys rosea f. catenula Inoculum on the Composting of Cabbage Wastes and the Endophytic Activities of the Composted Material on Tomatoes and Red Spider Mite Infestation” – The study examines the effects of inoculating organic vegetable heaps with the fungus Clonostachys rosea f. catenula on composting processes.