Red spider: how to prevent and eliminate this marijuana pest

Due to their resilience, high adaptability, and impressive reproductive capabilities, red spiders are one of the most common and most dreaded pests in cannabis cultivation. If these insects aren’t identified and eliminated in time, they can kill entire crops. The following article explains how to deal with this threat so that you can keep your grow healthy and red spider-free.

Red spiders are a pest that can attack both indoor and outdoor cannabis grows. Many experienced growers dread the arrival of these potential enemies, as they are one of the most aggressive infestations that can attack marijuana plants. And it doesn’t help that, if you’re unfamiliar with them, they can easily go unnoticed in their first stage of development.

These insects, which belong to the Tetranychidae family, developed in the Jurassic Period about 180 million years ago! This is prior to the division of the Gondwana supercontinent, and since then they’ve been feeding on plants. That’s why they are some of the most successful and prolific arthropod herbivores (organisms with exoskeletons) that exist today.

What are red spiders?

Two-spotted spider mites (Tetranychus urticae) are the ones that most often attack marijuana plants. As a matter of fact, they’re not spiders but mites, and are related to arachnids, just like scorpions and ticks. They are also very small and barely visible to the naked eye (measuring only about 0.5 mm).

They get their name from the two visible intestinal sacks on the back of their bodies, which turn black when they’re full. Sometimes, these sacks are noticeably absent, with adult red spiders adopting different shades of green, pink, orange, or deep red, depending on various factors related to genes, seasons, hosts, infections, and other physiological changes.

These mites live in colonies, which are most often located on the underside of the leaves, where they suck the sap and reproduce at the speed of light. That’s how they can quickly infest a marijuana crop and weaken the plants, hindering their development and preventing them from producing a decent flower yield.

How to detect red spiders in marijuana plants

The most important thing to remember to help prevent small red spiders from spreading and causing irreparable damage is to identify them at an early stage, before their numbers become too large. Unlike other more visible pests such as aphids or whiteflies, the tiny size of red spiders makes them really hard to detect with the naked eye; but you can always use a magnifying glass to help you find them.

Having said that, you can also look for something that’s more clearly visible, and that’s the marks that they leave when they’re feeding: small yellow, orange, or translucent spots on the leaves, which at first may appear as a stippling effect that’s produced by their bites. Many growers find these small and distinctive spots and think that they’re caused by some type of nutrient deficiency, without realising that it’s actually something much more sinister.

Red spiders reproduce at an impressive speed, as each female can lay between 5 and 20 eggs per day, or hundreds throughout her life. When the pest is already at an advanced stage, spiderwebs appear around the stems and even the buds of the plants. The spiders use these as barriers to protect the eggs against predators.

The web-spinning ability of red spiders also means that they can travel on the wind in ingenious silk balls. Unfortunately, though, when these spiderwebs appear, the pest is probably too widespread and there’s probably very little you can do to save your crop.

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What damage can red spiders cause in cannabis cultivation?

Depending on the level of development of the pest, the damage to marijuana plants can be more or less severe:

• Permanent discoloration (chlorosis) of the leaves.
• Blocked plant growth caused by stress.
• Lower yields, with smaller and lower-quality buds.
• If the pest is widespread, it can lead to the death of the plants.

How to prevent the appearance of red spiders

Prevention is definitely key for any grower. If you want to save yourself from lots of hassle, the best thing you can do is to take action in advance so red spiders don’t invade your home. To do this, you must consider the following golden rules:

• The best prevention always involves using pest- and disease-resistant marijuana seeds, which will help you greatly reduce the chance of these insects ruining your crop.
• Red spiders love dry environments and high temperatures, especially if they’re over 27ºC. Outdoors, it is impossible to control these parameters; but if you’re growing indoors, make sure your grow tent temperature doesn’t exceed 25ºC, and keep the humidity levels high during the vegetative phase (at around 60%).
• Keep your grow clean and disinfected. If you’re growing indoors, don’t go into the growing space with the clothes you wear outside, as you could be introducing this pest without realising it. Red spiders are an extremely common pest and have been registered in more than 1,200 plant species other than cannabis.
• Avoid an excess of nitrogen in your fertiliser, as high nutrient levels can also encourage their appearance.

How to eradicate red spiders

If red spiders have already settled onto your marijuana grow, you need to act fast:

1. Move the affected plants away from the healthy ones.
2. If you’ve already found the first signs of their presence, check your plants on a daily basis to manually get rid of both spiders and eggs (by rubbing cottonwool soaked in cold water or even some type of acaricide).
3. Remove the leaves that are most affected. If more than 50% of the surface of the leaf is damaged, it’s probably not worth keeping (and it might also be full of mites and their eggs).
4. Regulate temperature and humidity levels so that both are kept within the right parameters for your plants. This will create a hostile environment for these unwelcome guests.
5. Use organic remedies like Neem oil, potassium soap, pyrethrum oil, or sulphur. You might also want to introduce predatory mites such as Neoseiulus (Amblyseius) californicus, which feed on other mites such as red spiders.
6. Some growers choose more aggressive remedies to eliminate this pest, such as systemic chemical insecticides. However, these products aren’t recommended because everything your plants absorb ends up in your body once you’ve smoked their tasty flowers. Therefore, the best insecticides against red spiders must always be of a biological origin. If you do decide to use a chemical insecticide, though, remember that you’ll only be able to do so during the vegetative period: if you continue using it during the flowering phase, the plant won’t have enough time to remove this product from its system before harvest time.

Now that you know how to prevent, identify, and eliminate this pest, you’re ready to fight one of the number one enemies of cannabis cultivation. Don’t forget that healthy, well-maintained plants that are free from red spiders are always synonymous with abundant aromatic flowers brimming with resin. So happy growing!