Spider Mites
Im so glad you've found you’re way to this spider mites guide. That makes you one of the following types of cannabis grower:
1. Those that have have/had spider mites
2. Those that are going to get spider mites
We will show here the very best method of dealing with spider mites is to prevent their outbreaks in the first place along with tried and tested methods of treating infestations.
As the name suggests, these critters are part of the spider family and are tiny; adults measuring only 0.5mm. They are found everywhere and are commonly referred to as the glasshouse red spider mite or two spotted spider mite. They thrive in warm dry conditions and become a big outdoor problem during heat waves.
PREVENTION
You really don’t want an infestation to take hold so the very best advice we can offer is to take prevention very seriously. You may get away with being slack in the Winter but during Summer you are asking for it.
Invariably you will miss the arrival of these mites. They can enter your grow space through the air, on our clothes and direct introduction via cuttings. So we should begin by talking prevention
1. Grow from seed. Its high risk to grow cuttings from anyone else unless you can quarantine for several weeks before hand
2. Screen you air intakes – you could use an old carbon filter or a 180 micron screen. These will massively impact your flow so bear in mind when specifying duct and fan size
4. Avoid trips to the local grow shop. These places are teaming with mites since so many growers panic and rush here upon discovery of their issues
5. Have the very best environmental control and air flow
6. High hygiene standards in your groom at all times e.g. remove leaf waste immediately
Active prevention
Heres an Amblyseius andersonii which we will cover below. You can hang sachets of these handy helpers on your plants at any time and they will last 4 weeks. Should a single spider mite female enter and commence laying eggs, they will all be preyed upon immediately.
DISCOVERY
Despite of our best efforts, these pesky buggers are incredibly invasive and will do their level best to find and take habit in a nice warm dry environment – your groom. In general, adult females outnumber males 3 to 1. One adult female can enter your grow space and lay 100 to 200 eggs in a month. With correct conditions these eggs can be fully matured females in as little as 7 days, thats when all hell breaks loose if you are not ready and im sure you can start doing the maths in your head
By the time you see leaf damage there will already be tens or hundreds of breeding mites and the plant needs YOU NOW. The action you take now will decide whether or not you will be able to continue your grow. Do nothing and your plants will be dead within a couple of weeks. To identify spider mites you will need to use your loupe or microscope. You can see them with the naked eye as small dots. They are easy to see when they are active.
TREATMENT
The very best response to an infestation is to use a sequence and combination of CHEMICAL, BIOLOGICAL and ENVIRONMENTAL treatments. This will give you the best chance to eliminate all stages of the growth cycle and pick up any stragglers
CHEMICAL
It is widely accepted that the over use of synthetic and organic pesticides has led to resistance in the spider mite population. Their rapid reproduction rate will quickly throw up offspring that don’t die when sprayed. These are the most common spray treatments.
Pyrethrins - Pyrethrum 5EC for example
Neem oil
Azamax
DoctorZymes
Spinosad
Always spray treat your plants just before lights off to avoid phototoxicity.
Only DoctorZymes will kill all stages of the spider mite growing cycle, most importantly the eggs since its an enzyme. With that said you shouldn’t ever spray the plants down only once. Since eggs hatch in only 3 days in optimum conditions, a second spray down would take care of the new generations
Still there is a high probability you will have missed one of these microscopic devils. Remember what a single female can do again in only 7 days? It is recommended to reapply every 3 days continually until no traces of mites can be found
ENVIRONMENTAL
Spider mites are at their most reproductive in the high 20s degrees C and low humidities. It is a good idea to respond to an infestation by dropping your temps to sub 20 degrees and increase RH. This will dramatically increase the time they take to reproduce. During this time you can concentrate on decimating the current generations of adults and larvae
BIOLOGICAL
So we know prevention is always better than cure and this certainly applies to mites. We should add them to our plants before any spider mites have taken home in your groom.
However they are still incredibly effective when added after an initial treatment with your favourite spray. You must also drop your groom temperature to increase the reproduction time of the spider mites. Fortunately predator mites are happy breeding at lower temps and therefore will multiply in numbers quicker than the spider mites
Amblyseius andersonii
These soft tissued mites are effective from 10 – 30+ degrees Celsius. These are can be added in advance of any infestation as they are happy to feed on plant material and pollen. The sachets usually contain 250 of them and they live for 4 week. The cost is around 5 GBP for 5 sachets.
These should not be added to any large infestation and in particular to a high temperature environment where optimum growth is achieved by the spider mites. The predators just could not keep up with the accelerating numbers of mites
They eat all stages of the growth cycle and eat the larvae of other pests too
Phytoseiulus persimilis
These are true spider mite preds. They will only eat spider mites. You must only add them to an already established infestation or they will starve. These will breed quicker than any spider mite population. There are however more expensive and generally only available in large bottle quantities. These would be your last resort
OVERALL
Is it important to tailor the treatment according to where the effected plants are in their growth cycle.
Vegetative
You should use everything at your disposal and lots of it. Chemical + environmental followed by predators. If you have a photo plant, consider delaying flip until you are confident you are in control
Flower
Caution must be applied to the use of liquids sprays at any time after flowers have formed. Please have a look at the bud rot post for further info. DoctorZymes is an enzyme based treatment that also kills fungus and molds.
Likewise while humidity can be increased, caution should be applied to anything over 55% RH. Temperatures should be dropped sub 20. Again more info in bud rot post
Predator mites are your silver bullets here
FINAL THOUGHTS
Good luck and I wish everyone a fun pest free time. Keep observant, know your plants, leaves and mites should be identified early on.
Spider mites are everywhere and you really won’t eliminate them in entirety. You should think of it as a war of attrition just to keep the numbers down to where they are essentially harmless.
Anyone that has a plant late in bloom where mites have been left to cover the buds in webs should bite the bullet, should just do this, well almost
You have an excellent chance of diminishing an infestation caught in veg or early flower.
Thanks for reading, happy growing. Sorry if you're itching now.
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