Spider Mite Control in Marijuana Gardens

gore March 31, 2012 34
Spider Mite Control in Marijuana Gardens

If you have never heard of the two-spotted spider mite, then congratulations. Spider mites are a common garden pest that every indoor grower will experience eventually. Before we discuss treatment and prevention of this bug, lets get to know the spider mite a bit better.

Adult Two-spotted Spider Mite

Common Name: Two-spotted Spider Mite
Scientific Name: Tetranychus urticae [Acari: Tetranychidae]
There is some debate regarding the taxonomic placement of this garden pest, I have used  the name prefered by entomologists at U.C. Davis.
Affected crops: Too numerous to list. Let us focus on this pest as it applies to growing marijuana.

Description

Spider mites are very small, typically a mere 1/50th inch in length (.4 mm). The spider mites body is separated into two parts: the mouth or gnathosoma, and the body or idiosoma. The mites body ranges from green to yellowish orange, the Two-spotted spider mite is characterized by two dark spots on the idiosoma. Closer inspection will reveal the mites body is semi transparent, and the coloration of their spots are deposits of stored waste. Spider mites have six legs during their larval stage but grow an additional set as they enter their two nymphal stages of development. This additional set of legs remains with the mite throughout its adult stage.

Life cycle

Adults reach maturity in 5-20 days, depending on temperature. A single female spider mite can lay as many as 20 eggs each day and up to 200 throughout her life. The eggs, which she deposits on the undersides of leaves are spherical, clear and about 0.14 mm in diameter. After reaching maturity, adult spider mites live an additional 2 to 4 weeks. Two spotted spider mites have many overlapping generations each year and can rapidly increase their numbers.

Damage

Spider Mites have sharp, slender mouthparts used for piercing the plants epidermis. This puncture serves the mite by delivering plant sap that constitutes the mite’s primary diet. Injury sustained to the plant in this manner commonly results in a localized collapse of the hosts mesophyll tissue. Within hours the affected area develops chlorotic spots, resulting in lost productivity for that section of leaf.

Look for small yellow or bronze spots along your plants leaves. Spider Mites prefer to conduct their business on the undersides of leaves but soon expand their territory as the mite colony grows. Within days or hours plants can become completely inundated by mites and covered in webs that provide transportation to different areas of the host plant.

Treating infestation

Spider mite infestations can quickly grow out of control. The effects of uncontrolled spider mites can be so devastating that some growers abandon entire plants or indoor cycles. Minor problems during vegetative growth can quickly escalate into pandemic infestation a few weeks into flower.

By the third week of the flowering cycle, it is too late to use many popular sprays. One of the biggest concerns with spraying flowering marijuana plants is the potential for pesticide residue to affect the buds flavor or safety. Additionally, flowering marijuana plants tend to have greater phytotoxic reactions to sprays, which makes it easy to do more harm than good. If sprays must be used on flowering marijuana, reduce the light intensity by raising the lamps. After a day or so the lights may be returned to an appropriate height.

Considering the spider mite’s rapid reproduction, overlapping mite generations, and the ineffectiveness of sprays on eggs, regaining control can seem impossible. It is best to prevent infestation through a good integrated pest management program (IPM).

Effective Pesticides for Spider Mites

An entire rainbow of miticides are available at your local garden supply, or hardware store.  Many of these are perfectly safe for use, while others should be avoided.  When selecting pesticides be sure the product is approved for use on food crops.  Below is a list of some safe and effective sprays for spider mite control.

Product Active Ingredient  Degrades After Effective Against
Safer Insecticidal Soap Potassium salts of fatty acids 7-10 days Adults, nymphal, larval
Safer Bioneem Neem seed extract 7-10 days Nymphal, larval
Einstein Oil Neem seed extract 7-10 days Nymphal, larval
Dr. DoRights Colloidal suspension of herbal oils N/A Adults, nymphal, larval
PyGanic Pyrethrins 10 days on soil, 1-3 in air and water Egg to adult
SMC (spider mite control) Plant extracts, vegetable oil N/A Egg to adult

Most of the products  listed here are contact killers, so their effectiveness depends on spray coverage. Smaller plants can be dipped, to ensure even coverage but use special care with oils as they can trigger acute phytotoxic reaction.  Because sprays that are considered to be ‘safe’ are generally ineffective against spider mite eggs, a follow up treatment should be applied 4-7 days after the first.

Neem oil is an extract from the seed of the neem tree. The Azadirachtin found in this extract interferes with mite and insects ability to molt, affected bugs are then unable to enter their next stage of development.  Neem products are systemic, meaning they are able to enter the plants system and are circulated throughout the plant.

Blacklisted Miticides

There are specialized miticide sprays that can effectively treat infestation in as little as two applications. These sprays may sound like an attractive method for treating spider mites, but they are not intended for use on marijuana, vegetables or any crop grown for human or animal consumption. The sprays listed below must never be used on marijuana:

  • Avid
  • Floramite
  • Shuttle
  • Telstar
  • TetraSan
  • Hexygon
  • Forbid
  • Judo

These products are only approved by the Environmental Protection Agency (EPA) and/or the United Stated Department of Agriculture (USDA) for use on commercial ornamentals. To prevent misuse by amateur gardeners, many of these are not sold at your local garden supply store.

The only possible exception, while not technically legal, may be for use on marijuana crops not intended for consumption. The only example I can imagine would be a breeding program where seed is the only intended harvest.

Integrated Pest Management (IPM)

Spider mites adapt rapidly to adverse conditions; so control is best accomplished through a combination of methods.

Insecticidal and Miticidal Sprays

Avoid repeated applications of sprays that contain the same active ingredients. Spraying the same product repeatedly allows the mite population a chance to develop an immunity. Mites will almost always be present in different stages of development and insecticidal and miticidal sprays are rarely effective against mites in all stages of development. An application of spray might work to effectively kill all the adult and nymphal mites but spare mites in larval and egg stage. This means survivors, and survivors are bad for two reasons:

  1. Survivors will re-establish mite colonies.
  2. Mites which have survived one round of spray, can pass immunity to succeeding mite generations, thus weakening the effectiveness of the product.

To limit survivors, it is best to plan a rotating spray schedule of at least three products. This trifecta should include sprays that target mites throughout their various stages, from egg to adult.

Sanitation

In addition to sprays, spider mite colony suppression can be aided through responsible gardening practices

  • Remove dead vegetation from the plants and grow room
  • Keep floors and walls of the grow room clean and disinfect periodically
  • Quarantine clones and plants from outside sources
  • Regularly inspect plants for the presence of mites
  • Filter intake air and exhaust vent.

Keeping your operation clean is the real secret to mite control. Remember that the gardener can become an outbreak vector when mites are introduced to the growroom on clothes, shoes or gardening tools.

Biological Controls

There are several species of beneficial insects that can be used to control spider mites. If you choose to use a biological control to treat spider mites, be aware that some sprays are compatible with biologicals but others are not. Incompatible sprays will kill both the spider mites and the beneficial insects.

The most common type of beneficial insect used against spider mite populations are in fact, also mites. The species listed below are commonly referred to as predatory mites and have proven effective against spider mites under a variety of conditions:

Phytoseiulus persimilis
Wide Temp Range, Moderate Humidity:
Temperature Range: 55 – 105+ F.
Humidity Range: 55 – 90%
Further Information

Neoseiulus californicus
Moderate Temp Range, High Humidity:
Temperature Range: 55 – 90 F.
Humidity Range: 60 – 90%
Further Information

Mesoseiulus longipes
Widest Humidity and Temp Range:
Temperature Range: 55 – 105+ F.
Humidity Range: 45 – 90%

Ladybugs can also offer some assistance against spider mites but I don’t recommend them as the sole control method. Ladybugs will happily eat both predator and spider mites, so both should not be used together. My experience with ladybugs in grow rooms has always been a disaster. They seem to be overcome with a desire to fly into the light housings and die by the hundreds.  Ladybugs are much better suited for greenhouses.

Predatory mites and ladybugs are available from a number of direct sources, or can be purchased from your local indoor garden supply store. A regular contributor here at MGHQ has compiled a great list of predatory mite suppliers on our forum. Feel free to order from any of these reputable vendors, or add some that you may know of.

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34 Comments »

  1. Green Thumbcat May 28, 2012 at 12:15 pm -

    Please note that you’re talking about PLANTS, not SKIN.

    “Phototoxic” refers to damage to the skin from light. What you mean to say is “PHYTOtoxic,” which is the effect of chemicals on plant growth.

    Otherwise, very good and informative article, but make sure you look for and spot errors like this elsewhere on your site. You’re performing a valuable service. I’d like to help make it better.

    >^..^< Chairman Meow

  2. gore June 14, 2012 at 12:03 am -

    Thanks Thumbcat,
    I have made the edits.

  3. STEAMER July 22, 2012 at 6:49 pm -

    HELLO GORE HOWS IT GOING–I HAVE 3 LITTLE LADYS GROWING-CLONES AND HAVE A QUAD 50 WATT LED LIGHT AND WEATHER I PUT THE LIGHT CLOSE OR HIGH THEY SEAM TO BE GROWING AND SHOOTING OUT PRETTY GOOD-HOW MANY LUMENS DO I NEED TO MAKE THESE FLOWER-I WOULD LIKE TO STAY WITH LEDS IF POSSABLE-A FRIEND SAID TO BUY 2FT. TUBES-FOR 30 DOOLLARS-I HAVE 2FT-BY2FT.I KNOW I NEED TO ADD A ANOTHER LIGHT AND HOPEING I CAN GROW 3 PLANTS THANKS FOR ANY AND ALL HELP-STEAMER SAN DIEGO

  4. gore July 23, 2012 at 12:11 am -

    STEAMER,
    I’m going to give a brief reply to this because you posted it in an odd place, This article in about spider mites not lighting, but it’s ok.

    There is not real lux count that is required to grow marijuana indoors. But the more light you give them the better it works, every time. Personally I have still not met an LED fixture that I would endorse. However, LEDs should suffice for a hobby garden or to produce a few grams of smoke.

    Consider raising this question in the forum, where I and other members of the community have more room for discussion.

  5. Mark August 23, 2012 at 10:34 am -

    I was wondering I am in week two od the flowering stage. I have been using neem oil and dish soap for 9 days now and plan on using 12 more days so I can cover a three week cycle. If I give my outside plants three weeks to get rid of the neem oil and spray the leaves with a pump up sprayer a few times prior to harvesting do you think that will work? I want to make sure the oil is out of the plant and want to get rid of any eggs, dead mites and feces best I can. Do you think I could hang upside down and spray well with a garden hose after harvesting keeping a fan on to then help the drying process. Thanks for your help.

  6. kegs October 14, 2012 at 11:37 am -

    the predator mites work they are just expensive and they are almost dead by the time they get to you. i ordered 2500 and probably only got 50. slowly they do eradicate the problem. i suggest using them late in flower.

  7. craig October 28, 2012 at 3:26 pm -

    Pure Lemon LOil mixed at 1 tsp/quart water
    . Spray or sumerge in solution. Eggs and Mites Will be dead in hours………
    One Thorough application should be enough.

    Best Solution I have found.

    • Rambo October 28, 2012 at 4:41 pm -

      Interesting method. Has anyone else heard of or tried this?

  8. ccc1234 January 4, 2013 at 12:49 pm -

    has any1 heard of using h2o2 at 29% of course u have to delute it n know how much h2o2 to use

  9. Pete May 6, 2013 at 12:58 am -

    Another great article!

    Additional information

    Dichlorvos is found in No Pest Strips (NPS) and data regarding the risks of using these in marijuana grow rooms is pretty scant.

    Still, it is a very popular way to cheaply and completely get rid of spider mites, and since it breaks down in water (SOURCE: EPA), can be used in the vegetative cycle safety… just wash after. There seems to be no data on how it will effect the safety of flowering cannabis plants – but it is used by countless growers in flower (Subcool from High Times is a notable user of NPS) so what we definitely can say about NPS is that it does not effect the final products taste nor the plants vigor.

    Foliar sprayed NEEM oil effects the plants growth rate adversely by clogging their stomata. Of course, NEEM applied in the recommended quantity using a good delivery method will control mites and the cure is much better than the disease. If it is Sprayed after a few weeks in flower will that will effect the taste of the bud adversely.

    Other alternatives:
    Ice water sprays will slow mites down considerably.
    This can be used anytime and plants treated this way show surprisingly little shock. If I didn’t have any other means of control on hand and I saw a mite (or there damage) this would be my very first step in control.

    I will catch a lot of flack for saying this but…

    CO2 at 15000PPM, used for 4+ hours, will kill off mites and there eggs and anything else that requires oxygen to live. This is simply basic science. In an environment that is well sealed, you can achieve these levels surprisingly quickly. This is an advanced technique to mite control and should not be used in poorly sealed rooms, in shared spaces (i.e. residences where people live) because anything breathing oxygen in the space WILL BE KILLED (that means you, and your cat “Boots.”)

    One way the small time grower can take advantage of CO2 innoculation is by encapsulating the plants in a bag and loading the bag with CO2. For larger plants you can use mattress bags available at moving supply stores (like uHaul, etc)

    My plants where not harmed when treated in this manner. Some worry about the displacement of O2 from the root zone, but this doesn’t seem to be a problem and I’ve personally seen this method used effectively in soil pots and ebb and flow tables.

    For extra security, CO2 bomb twice in the period of two days, then again after 5-7 days.

    I have never seen a mite, or any other bug, able to survive this treatment!

    Rosemary Oil
    The active ingredient in SNS209 systemic soil feed
    Rosemary oil is something that mites just don’t like to eat. It does work as a preventative measure, but should be rotated like every other preventative measure.

    Other information

    Very low humidity (85) will cause mites to breed even more rapidly.

    A low nighttime temperature, (55-60) along with reasonable humidity levels are another excellent way to ensure that mite colonies don’t get out of hand.

    Experience tells me that when mites have a much harder time setting up shop in an environment that sees 55F nights – 75F day with 40-55% RH the whole time than in environments that sees 80F nights – 90F days at 30% RH.

  10. Larry June 2, 2013 at 1:35 pm -

    Hello, I’m very new to growing, and I just recently ordered safer’s 3-in-1 insecticide soap, and neem oil, I was wondering if someone would please email me the absolute best method for spider mites, this is my first grow, and I’d hate to lose my ladies :/ I will not be receiving my soap until Tuesday, what can I do for the time being? I’ve tried the green palmolive dish soap, and mixing a little chilli pepper into it, seemed to have slowed them down, but this is still an issue. Please help meh! lol. :) Thanks for your time.

    • Rambo June 10, 2013 at 10:54 am -

      There are a number of options but you remember whatever you spray on buds is going to get smoked. Your best bet is to rotate the products you use so they don’t become immune to any one method.

  11. Ann July 5, 2013 at 6:41 am -

    This is my first time at this, and I have a couple of ladies that have been visited by these nasty little creatures, & I have done my first batch of a neem oil spray solution. Now I’m wondering if I can clip or cut out the leaves that have the yellow spots on them? Or how about the really brown parts of the leaves? can I clip that part out?

    • Rambo July 9, 2013 at 1:00 pm -

      you can but you don’t want to remove to much green foliage. The plants are already stressed and removing foliage needed for photosynthesis will stress them further. Plants will drop leaves on their own if they are no longer needed.

  12. chang September 6, 2013 at 4:08 am -

    I once had Avid resistant mites. They drank that shit and laughed. So i got informed and this will work.

    Go to ebay and buy a COMBO miticide pack. Never just use 1 miticide over and over. You should be using 3 actually and then its real easy to conquer actually.

    1) Get a multi miticide pack from ebay. Search for “3 miticide” You want licensed miticide. No walmart shit here. This shit is dangerous. That’s a good thing.
    2) Mix it as directed. Don’t be a idiot and guess at ANYTHING.
    3) Rotate each miticide weekly if you still see them alive or getting worse by the 7th day. After 3 weeks tops and using each one it will be over. You win. Mites lose.

    • Rambo October 2, 2013 at 9:15 pm -

      but make sure you are using miticides that are safe for food crops and not just for ornamental plants.

  13. Tim September 10, 2013 at 10:03 pm -

    I got those little buggers from a clone from a friend. Fortunately, I only had 6 plants going at the time and I had just switched to 12/12 so I put ‘em in the shower, one at a time and rinsed ‘em real good using the force of the water to spray a lot of ‘em off and down the drain. Next I took 70% rubbing alcohol and diluted it to 35% by adding water and spraying the undersides of the leaves. The alcohol kills the mites and their eggs on contact. I then gave ‘em a shower again and a spraying again, for 3 days. I’d still find one or two but I ordered the predator mites and they took care of any 2 spotted ones and then started eating each other – that’s what they do – and I was totally successful in defeating them. But always isolating new clones for a week is my new rule to never be broken.

    • Rambo October 2, 2013 at 9:10 pm -

      creativity is a virtue. Good job

    • Deb January 23, 2014 at 6:04 pm -

      Does the alcohol really work?

  14. dgsco October 9, 2013 at 10:44 pm -

    1-2 weeks from harvest, and 2 of 9 get infested with two spots, the rest are not far behind. Perithreum (?) safe on buds? Hoping Dr. Doom can save the harvest from these little bastards.

    • Rambo October 21, 2013 at 12:50 pm -

      Thats a hard one. I don’t really like to use anything that close to harvest. My advice is drop the temperatures as much as possible to slow them down and consider nuking them with lethal CO2 Levels. I have heard some have good results increasing CO2 levels to about 12000 ppm for a few hours. Do a bit of research on this first.

  15. highzenburg November 6, 2013 at 12:42 pm -

    im having mite problems have tried everything,alchol,pesticides the works what do u suggest?just CO2?

    • Rambo November 19, 2013 at 5:30 pm -

      mites can be a huge problem and because growers are so bad at pest management that we have pretty much created super mites. Sometimes if all else fails, harvest early or scrap the plants and start over. Depends on how far along you are.

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  17. Old griwer February 8, 2014 at 4:55 pm -

    There is an electrical device that will keep any type of spider out of your garden or house. It’s called Riddex. Sold at Home Depot.

  18. kevin March 29, 2014 at 9:32 pm -

    I have been doing good I use endall I use it weak for a week then the next I use it stronger. I was wondering if there’s anything else that would be better than endall

  19. bj April 18, 2014 at 3:12 pm -

    I first noticed them late in vegetative stage, and began spraying them with a strong cinnamon/clove tea solution. Now a month into flowering, I’ve sprayed three times with Neem oil in weekly intervals, and still have a few adults and lots of eggs. I probably won’t win this, so my question is, what can I do to salvage the crop? Does freezing kill the mites and eggs? Can the buds be bagged and CO2 pumped in?

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  25. paul July 8, 2014 at 11:25 am -

    Hi I’ve got problem which I need help with I’m in 2 my 3rd week of flower and I’ve got spider mite not loads, I’ve sprayed them with bug cleaner but I think I’ve done the wrong thing. And suggestions ??

  26. joe August 21, 2014 at 11:26 pm -

    so my mites have gotten bad and i started seeing webs all over my plant and im 4 weeks into flowering, so ive done some research and i decided to try this: 1st i cut of all my leaves around the buds off and any unnecessary leaves, then in took a hose vacuum and literley put all my branches into the vacuum hose and sucked away all the adults and webs and a majority of the eggs were gone from removing the leaves, after that i took 1 gallon of water and put it in a simmering pan and put 6 habanero peppers diced in the pan for about 20 minutes and then strained it and put it in a spray bottle and sprayed the crap out of my whole plants and the surronding areas, then i let them sit for a bit and then ran the vacuum on them again. dont be shy with it anything that comes off while doing this was gonna fall of anyway. Also make sure you remove any leaves you take off the plant completely away from the plant. i did this for 4 days while waiting for my lady bugs to get to my house which i ordered of amazon to rid my plants of any extra eggs or adults. hope that helped some people i thought my plants were beyond saving but this allowed me to finish the whole grow cycle. in the end there will still be some mites and eggs but its not a big deal, if youve been smoking for a while i can almost guarantee you that youve baught weed with mites before and smoked it and it will not harm you