Spider Mites

Spider mites are a species of insects that every cannabis grower is familiar with. These small insects, that are relatives of spiders can be managed and prevented. 

Prevention

The first steps any grower takes to keep a pest free environment is preventative measures. There are a number if very simple steps any grower can do to prevent mites from entering their garden

  • A clean change of clothes and disposable Tyvec suits when entering garden
  • Seal interior and filtered Intakes and exhaust 
  • Foot baths with disinfectants and soap/iso spray bottle
  • Quarantine SOP’s for intaking any outside genetics 
  • Use products while rotating Modes Of Action consisting of repellents, feeding blockers/poisons and or fungal bacterial 
  • Propper PPE

Keeping a clean room and limiting any outside access to your garden is going to be your first preventative barrier. Using clean protocols where you only access your room in clean clothes or use a disposable suite another added measure commonly used is Isopropyl spray bottles to spray feet, legs, back etc… 

Know Your Enemy

Two-Spot spider mites will be the most common mite that cannabis growers will come in contact with. These mites will have 2 tell tale spots on their back/butt, this is an identifying trait seen in adult and mature two-spot mites. Upon hatching these mites will have 3 life stages, larval, nymph then their adult mature stage and can live up to 30 days. These mites can lay up to 20 translucent spherical eggs on the undersides of your plants leaves. This accelerated reproductive cycle allows these mites to slip in and establish populations very quickly. In optimal conditions around 80 degrees Fahrenheit maturation from egg to adult can take 5-20 days 

Spider Mite Damage

If on random leaves you are noticing light specs and general plant health decline, you may have the start of an infestation. Two-Spot mites are easy to see and spot. 

The method in which they feed, piercing the leaf’s subdermal layer and drinking the juices in the tissue is where the tell tale sign comes from. This speck looks like a slightly translucent spot, lighter than the tissue around it. Upon further inspection you will notice young, juvenile and/or mature mites and their eggs.  

Tiny Specks - the first sign of spider mite damage on marijuana leaves

Spider mite damage on a cannabis leaf Picture of spider mites on the leaf of a cannabis plant

Identifying Spider mites on the underside of the leaf. Don’t worry it’s not the end for this plant. There are plenty of well known and commonly used methods of control after an infestation is discovered.

This cannabis leaf shows the first signs of spider mites - click for a closer look!

These common pests eat your plants by draining individual plant cells over time that eventually die. The hole left by their piercing feeding mechanism is a common sign that mites have and may be currently in your crop. Scout and determine how extensive your infestation is. If you have plants where you have observed populations at 5 Mites a leaf per plant you have enough mites to warrant some extra measures. As a rule of thumb the first step is mechanical controls. Remove and dispose of as much plant material seen with mites or eggs as possible, this will help later with the efficacy of your application.

Extreme close up of the two-spotted spider mite - Tetranychus urticae - a marijuana grower's worst garden pest

Spider mites hibernate and like to hide so check everywhere for signs of life or feeding damage or eggs.

Early signs of mite damage.

Close-up of spider mite bites on a marijuana leaf

Spider mites and their eggs, found on the back of cannabis leaves

Spider mites and their eggs underneath the leaf of a cannabis plant - get rid of these pests quick!

Example of spider mites and their eggs on the back of a cannabis leaf

Because of their size and their ability to breed quickly many generations of mites can be living by the time a grower notices their intrusion into their grow. As their populations grow they quickly our grow their environment and will spread out and eventually make webs, the sign of an advanced population with many, many generations.

Example of webbing on a cannabis bud caused by spider mites

Spidermite webbing on a marijuana bud

Spider mites: like tiny inconsiderate ninjas

Under a microscope you can see they have four pairs of legs, no antennae and a body shaped like an oval.

A close-up of the dastardly so-and-so!
Image courtesy of University of Florida Entomology & Nematology Dept.

Spider mite webbing on a marijuana leaf - notice the bronze cast to the leaf - it's dying from all the tiny spider mite bites

With well established populations you will see entire buds/plants get covered in fine webbing from a spider mite infestation

A marijuana bud covered in webbing from spider mites

Here are adult spider mites with eggs
Adult female two-spotted spider mites with eggs and webbingImage courtesy of Natalie Hummel, Louisiana State University AgCenter, Bugwood.org

Assuming you currently have a clean room, the least invasive methods a grower can use to be ready for Two-Spot mites are preventative controls. Both preventative and reactive measure of control will help ensure a clean room of pest. But preventative will be your first line of defense.

Preventative Controls

A normal part of a preventative IPM program is making weekly/Bi -weekly applications that act as deterrents, repellants, insect growth inhibitors, growth/reproductive regulators. When used in a responsible program these applications will be rotated in use to change the Mode Of Action in order to decrease resistance. A products MOA is how the active ingredients or ingredient’s affect and interact with the target pest.

Some recommended preventative products are

  • Neem, the best being cold pressed products with a form of Azadirachtin with 3 active MOA this product is highly versatile 
  • Botanicals like Smite drown, paralyze, 
  • Translaminar products like Venerate act as feeding blockers and repellants
  • Even Captiva A capsicum product acts as a deterrent/repellent 

Reacting to an Infestation

Once a population of Two-Spot mites has established itself in your plants you will have to use some extra reactive controls. 

Increase the application interval of preventative controls, at suggested label rates and also add 2 or more MOA that directly act as a miticide/ovacide killing mites in various stages and their eggs. A good response program consists of 3 or more parts. Using ethical and safe products is up to each individual I highly recommend organic OMRI rated products and Bio-Insecticides for their safety and over all ease of use. 

  • Slow or prevent your pest growth/feeding or reproduction
  • Digestible Poisons, bactericides, fungal miticides, these will have dual affects and last longer as well as be very safe
  • Employ safe contact killers there is a litany of products meant to kill on contact, choosing one should be considered a final step in your program 

An affective program uses different MOA’s in rotation. You can switch out products for similar MOAs this rotation will also limit creating resistance. Some Pyrethrin’s caution against using more then 3 times a season. Swap it out for another approved contact killer making, sure the same stages of life will be targeted.

Beneficial Insects

Many growers rely on predatory mites to safe guard their crops as a preventative but mainly this option is best used in response to finding Two-Spot mites. Beneficial insects live to eat your target pest, their young and their eggs. Just like your Two-Spot mites, predatory mites like food that is living in an environment they like. Each mite listed below will only thrive in certain temperate environments, match your mites to your conditions to increase their life span. Also some mites will eat faster or a wider array of insects, Pesimillis eat voraciously and Californicus will even eat other predatory mites when their preferred supply of food runs out.

Beneficial Pest that predate on Two-Spot mites

  • Persimilis
  • Californicus
  • Andersoni 
  • Fallacus

 

 

Below are some other recommended products..

Azamax/ Azadirachtin is a very popular neem product and because of Azadirachtin’s 3 modes of its action, a feeding blocker, a Chitin synthesis inhibitor a growth regulator and a repellent. This chemical formulated when alone is also extremely safe for both you, your plants and your grow environment while still being very an effective form of both reactive and preventive controls.

Azamax is a time-tested way of killing marijuana spider mites A One-Hand Pressure Sprayer is perfect for misting plants

Mighty Wash – This product’s main ingredient is a known neurotoxin and while can be utilized safely, should be used as a last resort and or a cleanup spray at the during a 2-3 week IPM program for Two-Spot mites. This product must be used as directed and at label rates in order to remain safe, do not use on a blooming plant, Pyrethrin’s toxicity is about dosage so using appropriate Personal Protective Equipment as directed by label will linit exposure, pyrethrin’s generally break down quickly in the presence of sunlight and water. Always spray with lights off and in temperatures under 78’ F, pyrethrin’s are known to have phototoxicity in direct light after spraying, leaves lights off until 4 hours after spray has dried. 

Mighty Wash kills marijuana spider mites A One-Hand Pressure Sprayer is perfect for misting plants

Spinosad Products (safe & organic) – Spinosad products are organic and unlike many other spider mite pesticides, this is moslty harmless to pets, children, and plants. Unlike many insecticides, you can spray spinosad heavily on leaves and roots with basically no negative effects. Spinosad products can be used directly to kill spider mites on contact, but can also be used when watering plants to systematically kill spider mites via the roots. Spinosad can also be effective at fighting caterpillars, thrips, and many other marijuana pests.

Can be used both as a topical spray like Azamax and Mighty Wash, and can also be used directly at the roots. Spinosad is an organic insecticide made from the fermentation of a specific soil bacteria (actinomycete Saccharopolyspora spinosa) and kills spider mites via ingestion or contact by effecting the insect’s nervous system. Spinosad can be a good choice for organic and outdoor growers, because it is very toxic to spider mites, but is less toxic to many beneficial arthropods.

Note: Most spinosad products are effective for only about 24 hours after being mixed with water, so only mix as much as you will need per application. Anything left over will be waste. You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly.

Recommended: Monterey Garden Insect Spray with Spinosad

Spinosad products are organic and kill spider mites, caterpillers and thripsA One-Hand Pressure Sprayer is perfect for misting plants

Essentria IC3 (organic)

Essentria IC3 Insecticide is a mix of various horticultural oils that is organic and safe for humans. It is often marketed as a “bed bug killer” but it can be effective against many bugs, including spider mties, when the plants are treated regularly. Unfortunately it only stays effective on the plant for about 8-12 hours so you will want to either apply this daily or (better idea) combine with other options. You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly.

Get Essentria IC3 insecticide on Amazon.com - this can be a tool in the fight against broad mites or A One-Hand Pressure Sprayer is perfect for misting plants

Get Inseticidal soap to kill cannabis aphids - available on Amazon.com!

Insecticidal soaps

M-Pede’s active ingredient is Fatty acid salts.Insecticidal soaps weaken the outer shell of spider mites but are safe for humans and don’t leave much of a residue.

With soaps, coverage is very important as it does not stay on your plant for long, so follow-up applications may be necessary.

Although this is considered safe, I would not recommend using this on blooming plants.

Doktor Doom Spider Mite Knockout Spray – This spray is hard on spider mites, but the main ingredient Pyrethrum can also be hard on plants, especially in tight spaces without much ventilation, so keep it as a last resort if possible. Use with extreme care around humans as the ingredients can be toxic. Never use Pyrethrum-based products on your plants while your grow lights are on as it can burn your plants. Avoid using Pyrethrum products on young or sensitive plants as they can get burned even when the lights are left off.

Do cover your grow lights and vents when bombing your plants with Pyrethrum and make sure you give the area at least 24 hours to air out before you try to breathe the air. This spray can work well for a couple of plants, but you’ll want a Pyrethrum fogger if you have a lot of plants to treat. Outdoors, Pyrethrum can kill beneficial insects too, so keep that in mind if you’re using natural predators to control pests (like ladybugs). All that being said, this spray will work to get rid of most spider mites, and it kills them on contact. Pyrethrum kills spider mites but not their eggs, so this product usually needs to be used 2-4 times (once every 2-3 days) to stop the breeding cycle and get rid of the toughest infestations.

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Floramite – Strong stuff with harsh chemicals, incredibly expensive, but it can often do the job when everything else fails. Use as directed and only as a last resort!

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SM-90 mixed with water (1 part SM-90 to 5 parts water) kills spider mites on contact and is organic (it even smells good!). You will need a mister to get nice even coverage on all the leaves with SM-90.

Diatomaceous Earth – Basically, this is fossil dust – sprinkle on the top of your soil, and anywhere else in your room (window sills, doorways, etc). This powder-like substance is harmless to mammals and plants, but is incredibly sharp at the microscopic level. Therefore it will tear and dehydrate spider mites on physical contact. This will not get rid of an infestation, but can help control and slow things down when used effectively.

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