Spider Mites

Spider mites are not insects but are tiny arachnids, related to spiders and ticks. The most common species that targets cannabis is the Two-Spotted Spider Mite (Tetranychus urticae), but other species like Russet Mites also pose a significant threat.

Adults are less than 1mm, often pale green or yellowish, with two dark spots on their backs. They are difficult to see with the naked eye.

They feed by piercing plant cells and sucking out the contents. This feeding activity causes the characteristic yellow or white stippling (tiny dots) on the upper surface of leaves. As the population grows, the stippling merges, causing leaves to appear sickly and discolored.

The fine webbing is their most telltale sign. They use it to travel from leaf to leaf, protect their eggs, and escape from predators. The webbing can become so dense that it can cover entire buds and stems.

This is their most dangerous trait. A single female can lay hundreds of eggs in her lifetime. Under ideal conditions (warm temperatures and low humidity), a new generation can hatch and mature in as little as 5-7 days, leading to an exponential population explosion.

These are even smaller than spider mites, often requiring a 60x magnification lens or higher to see. They are a bronze or tan color and are shaped like a wedge.

Russet mites do not create webbing. Their feeding causes a distinct "bronzing" or "rusting" of the leaves. Leaves may also curl downward, become brittle, and develop blisters or a shiny, wet appearance. This damage is often mistaken for nutrient deficiencies or heat stress.

Like their larger cousins, russet mites reproduce incredibly fast and can spread through a garden with devastating speed.

An ounce of prevention is worth a pound of cure, especially with mites. The following practices are non-negotiable for a healthy, pest-free garden:

Isolate any new plants, clones, or cuttings for at least one to two weeks. During this time, inspect them daily with a magnifying glass.

Keep your grow area clean. Sweep up debris, remove dead leaves, and sterilize your equipment between grows.

Use fine mesh screens on all intake vents to prevent pests from entering.

Spider mites thrive in hot, dry conditions. Maintaining a relative humidity (RH) of 55-65% and a temperature below 78°F (25.5°C) can significantly slow their life cycle and reproduction.

Make it a habit to inspect the underside of leaves on random plants daily or every other day. This is where mites live and lay their eggs. Early detection is your best weapon.

Once an infestation is confirmed, a single treatment will not work. The eggs are often resistant to sprays, and the rapid life cycle requires multiple applications to break the cycle. A multi-pronged approach is necessary.

For small, localized infestations, you can use a small hand vacuum (with a HEPA filter) to physically remove mites and webbing.

Remove and destroy heavily infested leaves, branches, or entire plants to reduce the population. Do this carefully in a way that doesn't shake the mites onto other plants.

Use a strong spray of water to physically dislodge mites from leaves. Ensure you target the underside of the leaves. This is only a temporary fix.

A powerful, all-natural pesticide. It works by acting as a repellent, an anti-feedant, and by disrupting the mites' life cycle. Important: Only use on plants in the vegetative stage. Do not use neem oil during flowering, as it can ruin the taste and smell of the finished product.

This spray works on contact by breaking down the mites' outer cuticle, causing them to dehydrate. It is safe for most plants and can be used sparingly during early flowering if necessary.

A natural pesticide derived from chrysanthemums. It works by affecting the mites' nervous system. Use this with caution, as it can harm beneficial insects and is toxic to fish.

Sprays made from rosemary, peppermint, or cinnamon oils can act as a repellent and contact pesticide.

These are a grower's best friend. They are highly aggressive predators that only eat spider mites. They are a great solution for severe infestations. Release them directly onto infested plants.

These predators will eat a variety of soft-bodied insects and mites. They are an excellent preventative measure and can help with early infestations.

The single most important thing to remember is the life cycle. If you don't repeat your treatments, you will only kill the adults, and the eggs will hatch, restarting the problem.

Spider mites love the underside of leaves and stems. They are also often concentrated at the top of the plant under grow lights where it's warmest. Always spray and inspect these areas thoroughly.

Russet mites are the silent killers. The absence of webbing can be misleading. If your plants show signs of bronzing, rust, or unexplained stress, check them with a high-power microscope immediately.

Be extremely cautious with any spray or pesticide on a plant intended for human consumption, especially in the flowering stage. Pesticides can be absorbed and can ruin the final product. Stick to biological controls and natural oils during this phase.