Common microscopic mites found in cannabis plants
They are arachnids. Since not all of them are considered an agricultural pest, we'll just focus on the 3 common and devastating mites generally attacking marijuana plants:
Tetranychidae
The most common type for the red spider mites (Tetranychus urticae) belong to this family. They have 4 pairs of legs and are about 0.2 in long. They suck up the sap of plants leaving some little yellowish dots on the leaves. At an advanced stage, their presence becomes more evident due to the emergence of cobwebs.
Just like most arachnids, they reproduce sexually. Mites go through a 3-stage lifecycle: larva, nymph, and adult. This family is not the one with the tiniest bugs, so even when the infestation has taken over the entire cultivation, we'll be able to come up with a way to get rid of them. Make sure the remedy is effective enough, though.
Tarsonemidae
Living up to their name, these microscopic mites are just 0.04-0.11 inches long. Whitish or yellowish-green, females have 4 pairs of legs while men have 3 pairs of legs and two rigid claws to carry the nymphs (during the stage between nymph and adult) and hold the female during copulation.
Given their small size, Tarsonemidae are very difficult to combat. However, if you manage to find the main source, you may still be able to stop their development and, in turn, save your plants. There are two species of Tarsonemidae: Polyphagotarsonemus latus, also known as broad mites, and Polyphagotarsonemus pallidus, also known as cyclamen mites.
If broad mites have settled in your cultivation, it's time to start worrying for it may reveal the presence of flying invaders such as thrips (Frankiniella occidentalis). Thrips allow broad mites to move around freely because the latter hang off their legs to travel to other parts of the cultivation and infest them for good.
Eriophydae
These microscopic mites are between 0.04 and 0.08 in long, which explains their amazing endurance. They build their habitat in one little corner and simply go unnoticed.
Whitish with only two pairs of legs, they feed off living tissue because dead plant material has no nutritional value for them. To perform their attack, they use 5 little needle-shaped limbs with which they inject their saliva generally containing several plant viruses. That's how plants become infected and develop severe malformations as well as lumps. Calepitrimerus vitis is a tiny eriophyid mite, also known as grape leaf rust mite, that leaves brownish rusty-looking dots in its path.
How to detect a plague of microscopic mites
With the help of a magnifying glass with magnifications of x100 or x200, these little 0.04-0.2 in long mites can indeed be spotted. If you do not have one at hand, you risk detecting the plague when it's already too late to save your cultivation.
In most cases, microscopic mites being visible to the naked eye means that the infection is well advanced and has taken over your entire crop. They are in fact so tiny that, in a single 0.3 in2, we could find thousands of them. So imagine how devastating they can be. Microscopic mites can become a true nightmare for the grower since it's actually one of the hardest-to-beat plagues attacking cannabis plants. Why? Because they're tiny, they know how to hide out and they reproduce at the speed of light.
The best way to detect their presence is by observing both sides of the leaves. The most common symptoms are yellowing foliage and dropping leaves. Spiderwebs could also be a telltale sign if Tetranychidae are around. The plant's growth will also become stunted. With all this information, you should be able to spot a spider mite attack, among others.
If plants start to grow more slowly and you find malformations or lumps in young leaves, a plague of Tarsonemidae is definitely attacking your plants.
If the growth has also been affected but you've noticed a kind of swelling growth instead, then it's a plague of Eriophydae mites.
How to effectively get rid of microscopic mites
As the saying goes, prevention is better than cure. The first step would be to keep the grow area clean and tidy, making sure it's thoroughly cleaned on a regular basis. Remove any dead plant matter and create the perfect environment for your plants. This reduces the likelihood of your plants being attacked by this kind of pests.
Biological pest control of grape leaf rust mites (Calepitrimerus vitis)
To combat this tiny eriophyid mite, you can use either Typhlodromus pyri, Typhlodromus phialatus or Kampinodromus aberrans. If you decide to use complementary plant protection products, you may have to ensure they don't affect the beneficial microbes in the soil first.
Chemical pest control of Calepitrimerus vitis
Abamectin, Acrinathrin, Azadirachtin, Sulfur, Pyridaben, Fenbutestan, thiazodiline, fenoxipiridazol, urea, Propargite, Spirodiclofen.
Biological pest control of tarsonemidae mites like cyclamen mites (Polyphagotarsonemus palidus)
Use biological predators such as Amblyseius swirskii and Amblyseius californicus (the latter is also really effective against spider mites) and you'll see how quickly they disappear, especially with high temperatures and low humidity levels.
Chemical pest control of Polyphagotarsonemus palidus
Sulfur, Dicofol, Endosulfan, fenbutestan, and Hexitiazox.
Biological pest control of tarsonemidae mites such as broad mites (Polyphagotarsonemus latus)
Using the very same biological predators you would for fighting cyclamen mites should be enough.
Chemical pest control of Polyphagotarsonemus latus
The same as against Polyphagotarsonemus palidus.
Some preventive tips to avoid being caught off guard
- Keep new clones quarantined for a few days.
- Don't use the same clothes to visit different grows.
Avoid contamination at all costs. If you happen to visit an infected grow, you'd better clean both your hair and body and change clothes before visiting another cultivation.
If you don't bear this preventive measures well in mind, your grow is likely to end up having some unwanted visitors.