Seedsman Blog

HOW TO DEAL WITH COMMON CANNABIS PLANT PATHOGENS: SPIDER MITES

We’ve already taken a look at some of the fungal threats which can encroach on your precious plants. In this article, we examine a different kind of headache – Spider Mites.

Spider Mites (Arachnid Tetranychus Urticae)

What are they?

Spider mites are tiny terrorists who lurk in the foliage of your crops, wreaking havoc as they chew their way through the leaves. As if that wasn’t bad enough, these pests lay eggs in the leaves, meaning they can ultimately grow their own backup. Spider mites tend to be more common in soil grows than in hydroponic setups, but can appear anywhere Cannabis is being cultivated.

What do they look like?

Here’s the problem – they’re absolutely tiny. It wouldn’t be a bad idea to invest in a magnifying glass or a hand-held microscope as part of your troubleshooting toolkit, because if you want to catch these troublemakers early, you’re going to have to turn sleuth. Unfortunately, it’s far easier to spot the handiwork than it is to spot the culprit, and by the time the symptoms show, you’re playing catchup. The mites themselves have oval bodies, four pairs of legs, and no antennae, but they’re far too small to see such detail with the naked eye. When carrying out your regular inspections, look for tiny speckles on the leaves which appear similar to pinpricks, only typically yellow, orange or white in colour – these are actually bite marks, and are one of the earliest signs of invasion. Spider mites often hang out on the underside of the leaves, and so inspection will have to be extremely thorough. Often, the first sign of spider mites is a ghostly-white webbing which gives a haunted appearance to the leaves and buds. This webbing is spun by the mites to protect themselves from the elements and other predators. At this stage, it’s too late to act.

What do they do?

Spider mites feed on plants by piercing individual cells, then sucking out the nutrients contained within the cells. By feeding on the chlorophyll, they disrupt photosynthesis, starving the plants of their ability to manufacture food and causing a quick death to the plant. The collective appetite of spider mites is huge, and infestation can kill plants overnight. They also lay eggs on the plant surface, and since they can easily amass huge numbers (A single female spider mite can spawn a million reinforcements in a month) before symptoms of infestation are noticed, they’re understandably one of the more despised – and challenging – adversaries faced by cultivators.

How do they get in?

One of the most common ways to acquire spider mites is by bringing plants or cuttings in from the outside. Adding a pre-infected plant to your growing environment will spell disaster for you and provide spider mites the kind of all-you-can-eat buffet they thrive on, so if you ever receive an outside plant, or bring in a cutting, isolate that plant in a quarantined environment well away from your precious grow for a minimum of two weeks. In that time, check it regularly with a handheld microscope or magnifying glass, and make sure it’s infection free before allowing it anywhere near the rest of your plants.

How do we stop them?

Unfortunately, with great difficulty. Spider mites don’t typically respond to just one treatment, and can actually develop resistance to many methods utilised to bring about their demise. It’s recommended to take a multi-faceted approach when attempting to eradicate this threat.

  • Predators – Among the methods recommended to combat spider mites is to introduce predators – yes, predators. Other insects, such as Ladybirds, can be brought into your growing area to hunt and kill spider mites. These can be obtained from most head shops, then let loose to go after the mites, without harming the plants. The humble Ladybird just went up in my estimation, however, it must be noted that this approach is unlikely to completely and effectively eradicate the problem, due to the sheer number of mites and the speed with they typically reproduce.
  • Pruning  – If faced with a smaller infestation, prune away any infected areas, and be prepared to bite the bullet – prune well beyond any areas of webbing to make sure you’ve trimmed clear of infected areas. Discard the cuttings safely. If you’re dealing with a large infection on a plant, be prepared to destroy the entire plant to avoid the risk of the mites spreading to nearby plants.
  • Hosing – Gently, but thoroughly, hose down your plants after pruning. This is a useful step to help remove any remaining mites. Hosing periodically is prudent if mites are regular visitors to your garden, as mites prefer hot and dry conditions. Mixing a 9:1 ratio of water to alcohol is known to kill mites without damaging plants.
  • Improve air circulation – Employing the use of a few fans in your garden can help keep spider mites off the plants
  • Essential Oils – Neem oil, Peppermint oil, Cinammon oil and Lemon oil can be mixed with water and sprayed on plants to prevent mites without any risk – but avoid spraying the buds, as these aromatic oils may alter their taste or smell.

Spider mites are a different type of threat, but no less of a threat than any other deadly pathogen. As always, check your plants regularly, know what to look for, and act quickly.

Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.

This post is also available in: French

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Duncan Mathers