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How to Prevent Spider Mites In Cannabis Plants

Spider mites can be detrimental to your cannabis plants/ read on for a detailed look at what spider mites are and how you can prevent them in your grow area.

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Cannabis, just like any other plant, is susceptible to garden pests which, despite their size, can have devastating effects on a plant’s ability to grow and develop.

In this article we look at spider mites, arguably one of the most common pests affecting cannabis plants. We’ll show you exactly what they are, how to get rid of them and how to prevent them coming back.

For more articles like this and the latest cannabis-related news, grow tips and more, bookmark our site and check in with us regularly. Also, make sure to check out our earlier post for more tips on cannabis pest prevention.

WHAT ARE SPIDER MITES?

Spider mites are a common garden pest that generally lives on the undersides of plant leaves, where they may spin protective silk webs to protect themselves against the elements and other predators.

They are less than 1 millimetre (0.04 inches) in size and can be red or black in colour. Spider mites prefer hot, dry conditions and lay transparent eggs which can hatch in as little as 3 days.

Hatchlings are sexually mature in 5 days, and female mites can live for up to 2-4 weeks, laying up to 20 eggs per day.

TELLTALE SIGNS OF SPIDER MITES IN CANNABIS PLANTS

Spider mites feed off cannabis plants and cause damage by puncturing plant cells in order to feed. Spider mites affect both indoor and outdoor plants and can wreak havoc when not controlled quickly.

Spider Mites pest cannabis detection

Some initial signs of a spider mite infection include tiny spots or stippling on leaves (caused by feeding) and thin, silky webs surrounding the underside of plant leaves and branches.

Larger colonies can cause leaves to turn yellow, become limp and eventually, die off altogether. A large spider mite infection can have a significant effect on a cannabis plant; by destroying the plant’s leaves, they may stunt its ability to grow and develop, eventually resulting in lower yields.

Spider mites may also infect the surrounding areas of buds, which can affect their ability to develop and mature properly. Finally, a large enough colony can kill entire plants, although that is very uncommon.

HOW TO CONTROL AND PREVENT SPIDER MITES

We do not recommend using chemical pesticides on spider mites. In most cases, this will only make matters worse by killing off other insects that prey on the mites.

Also, spider mites are notoriously good at developing resistance to common pesticides, so we suggest using some of the organic methods outlined below.

We also recommend addressing any environmental factors first, then following up by pruning and hosing down your plants.

ENVIRONMENTAL FACTORS

Remember, spider mites like hot and dry conditions. So, before you get started on any kind of countermeasure against a colony, try bringing down the temperature in your grow room (if possible, bring them down past 20ºC or 68ºF but be careful not to damage your plants).

Next, create some extra air circulation in your grow area. Spider mites hate windy conditions.

PRUNING AND HOSING

Once you’ve addressed any environmental factors in your grow area, it’s time to start pruning.

If you’re only dealing with a small infestation, cut down any infected areas well past the mites’ webbing and discard them in the trash. If you’re dealing with larger infections on individual plants, consider destroying them to avoid the mites spreading.

Once you’ve pruned your plants, consider hosing them down gently. This will help remove any remaining mites and will also help prevent another infestation. You may want to hose them down periodically if you find you’re dealing with mites on a regular basis.

Once you’ve done all of that, you may want to use one of the below control methods to minimise the risk of a future infestation. Remember to check up on your plants daily and to repeat treatment at least twice to avoid having the mites coming back.

Note: some growers hose down plants with a mix of water and alcohol (9:1 ratio). This mixture is known to kill mites on contact without damaging plants.

ADDITIONAL WAYS TO CONTROL SPIDER MITES

INTRODUCE OTHER INSECTS

Ladybugs, lacewings and predatory mites prey on spider mites and are generally available commercially. For the best results, introduce these insects when mite populations are low.

Ladybugs are by far the most common insect used to counter a spider mite infestation. For more detailed tips on how to use ladybugs in your garden, click here.

Other insects that prey on spider mites include:

  • Sixspotted thrips
  • Minute pirate bugs
  • Bigeyed bugs
  • Western flower thrips

ORGANIC INSECTICIDES AND INSECTICIDAL SOAPS

There are a number of organic insecticides on the market that can help control a spider mite infestation. Here are some popular solutions we recommend trying:

  • Essentria IC3: Containing a mix of horticultural oils, this organic spray can be directly applied to your plants using a mister. However, the spray only remains active for 8-12 hours, so you may need to use it daily or combine it with another product or control method.
  • Spinosad: These products are completely organic and do not damage plants. You can apply any of these products to your plants during an infestation to kill mites on contact or add them to your plants’ water supply for long-term protection against mites and other pests.
  • NukeEm: This is a relatively new insecticide made from food-grade ingredients. It can kill mites the egg, larvae or adult stage, and doesn’t leave any residue on the plant.
  • SM-90: An organic wetting agent with a beautiful aroma. Mix this with water and apply it to your plants with a mister to kill any mites on contact.
  • Insecticidal soaps: Insecticidal soaps are great for spot-treating infested areas of your plants. They leave very little residue on your plants but you should still avoid getting any directly on your buds. Multiple treatments may be necessary as soaps do not stay active for long.

ESSENTIAL AND HORTICULTURAL OILS

There are a variety of essential oils that can help to kill and control spider mites by attacking their central nervous system.

Neem oil extracted from the nuts of the neem tree) is considered a miticide and is the most common type of essential oil used to control mites. However, there are plenty others out there, including:

  • Eucalyptus oil
  • Cinnamon oil
  • Lemon oil
  • Peppermint oil
  • Rosemary oil
  • Eucalyptus oil
  • Cinnamon oil
  • Lemon oil
  • Peppermint oil
  • Rosemary oil
  • Eucalyptus oil
  • Cinnamon oil
  • Lemon oil
  • Peppermint oil
  • Rosemary oil
  • Eucalyptus oil
  • Cinnamon oil
  • Lemon oil
  • Peppermint oil
  • Rosemary oil

These oils can be mixed with water and liberally applied to your plants. However, many of these oils are very aromatic, so you may want to avoid getting them on your buds to avoid changing their taste or smell.

Alternatively, you may want to treat your plants periodically with horticultural oils. We generally recommend using vegetable oils, such as canola, soybean or cottonseed.

Spider mites prey on cannabis and can have a huge effect on your yields. Click here to learn how to keep your cannabis plants safe from spider mites.

In My Grow

Taking the mystery out of cannabis

The Two Spotted Spider Mite and the Cannabis (Marijuana) Plant.

Spider mites are one of the most common pests that cannabis growers are going to run into. If they’re left unchallenged and allowed to get comfortable they will be devastating to a crop. So instead of doing battle with these little bastards I suggest developing an Integrated Pest Management (IPM) program suited to your conditions. A good place to start is to have clean grow area, don’t give pests a reason to want to hang out. The next step is to know your enemy.

What are they?

  • Tetranychus urticae Koch (Two spotted spider mite) is considered a general feeder, which means it attacks a wide variety of plants.
  • It’s sometimes also known as the “red spider mite” and the “greenhouse spider mite”.
  • This pest gets its name because it typically has at least two spots. One on each side of its body, just behind the eyes, while the top of the abdomen is free of spots. These spots are made by pigments in the digestive system, that’s why the number of spot and the pattern can be different between individual mites.
  • Adults and nymphs have four pairs of legs and typically have a yellow or greenish color. They’ll also have hairs or spines on there body.
  • The adult male is smaller than the female and has a pointed abdomen. It sometimes has an orange or brown color and is more active than the female.
  • The adult female is about 1/60 of an inch long but will be bigger than the male and more oval shaped.
  • The female is usually a pale leaf-green, but it can have a yellow, brown and orange tint. .
  • After a single mating, females are fertilized for life and will lay her eggs on the underside of leaves at the rate of 2-6 a day. Each female may lay as many as 100 during her lifetime, about 75% will be hatch female to 25% male.
  • The eggs are spherical, clear, and colorless when laid but will become pearly white by the time they hatch.
  • The red eyespots of the embryo are visible just before they hatch.
  • The young mites that hatch are larvae and they look exactly like the adults except they’re smaller and have only three pairs of legs
  • Right after it hatches it’s kind of translucent (except the red eyespots), but after it starts feed on the plant juice, it’ll turn pale green and the black spots begin to form.
  • Depending on the weather or indoor growing conditions, a complete generation of this pest could be completed in 7-20 days.
  • With the right conditions generations will overlap and all stages can be found on most outdoor plants during the summer months. Hot dry weather and low humidity helps the development of severe pest infestations.
  • The young mites shed their exoskeletons three times before becoming mature.
  • When tempuratures drop outdoors the twospotted spider mite adult female will change to an orange color and overwinters in places like underneath bark scales or ground cover around the base of plants and trees (most other species of spider mites overwinter as eggs on the host plant).
  • Only the females are known to overwinter. As the temperatures increase the females start feeding again and slowly lose their orange color and get their normal greenish color and the spots return.
  • Overwintering females lay an average of 39 eggs over a lifespan of 23 days, alot less than their summer born sisters.
  • These eggs could take up to 3 weeks to hatch, depending on temperature. After that, the generations start to overlap. Summer-form females can lay about 100 eggs over a period of 30 days.

Environment

  • They love the warm dry summer months and thrive in artificial environments that are between 70 – 80 F with low humidiyt. A high mite populations often shows up with hot, dry weather.
  • They like to hang out and lay their eggs on the underside of the cannabis leaf. Because of their small size and their love for feeding on the underside of leaves, it’s easy for them to go undetected until the little buggers have caused serious damage to a plant.
  • Some of the plants that they love to live on are field crops, house plants, vegetables, small fruits, shade/fruit trees, shrubs, flowers, CANNABIS and some grasses, just to name a few.
  • Mite and their eggs are often hard to see clearly without using magnification. But they’re not hard to find, just hold a white sheet of paper under a branch and sharply tapping the branch against the paper. If mites are there, they will show up on the paper as tiny, moving specks.

What does damage look like?

  • Two Spotted Spider Mite damage looks like Whitefly damage because they feed in a similar way.
  • Mites feed by inserting their mouth parts into leaf and sucking out the life juice, including the chlorophyll (that’s how they get the greenish color). The damage will first look like white spots, giving the leaves a stippled appearance. As they continue feeding, the affected leaves take on a brown hue, commonly called bronzing.
  • Light infestations usually go unnoticed, it’s only with a heavy infestations that the leaves will look chlorotic (yellow), stippled, or mottled in appearance.
  • Mite feeding substantially reduces bud production.
  • Eventually the infested leaf will die and fall off.
  • With closer examination an infested plant will have fine, silken threads over the foliage, twigs, and branches.
  • These silken threads are produced by the mites as they move across the leaf surface. When a plant is severely infested they will usually have a fine cobweb appearance on the underside of the leaf and buds.
  • The twospotted spider mite loves to producer of webbing.

How to fight them?

Biological controls

  • Predatory mites are more effective than chemical control because the pest mites do not build up resistance to predatory mites and growers can reduce or eliminate the use of chemical pesticides.
  • Predatory mites do not bother plants, people or animals.
  • Because predatory mites do not give immediate control, they need to be released at the first signs of a pest mite problem. If there are no pest mites for food, predatory mites will not survive or reproduce.
  • Other insects are also good predators, such as the six-spotted thrips, Feltiella acarisuga, and general predators, such as ladybugs and lacewings.
  • The predator mite that I’m able to get from a local insectary is the Phytoseiulus Persimilis. This bug specializes in killing web-spinning mites like the carmine red, two spotted and Pacific mite. They’re most effective when the temperatures are between 59-86F and about 60% humidity.
  • The Persimilis can reproduce pretty fast, which helps if your spider mite population is getting worse but you don’t have an infestation yet. Rincon-Vitova suggests treating sudden hot spots by releasing 1 mite per 100 spider mites for control within 1 week. Don’t forget once the food is gone they will eventually die of hunger.
  • Bean Plants are a great tool to use to use against spider mites I’ve learned. They’re really good at attracting mites away from infested plants. It’s suggested to have single bean plants growing in small container or disposable cups. That way when the bean plant looks full of mites you can just remove it and replace it with a fresh one. Also, mite damage shows up within hours on bean plants, where it may take a day or two to show up on cannabis.
  • Video of spider mite interactive study https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4211727/

“Since Spider Mites hate high humidity and if your not battling Botrytis or other molds. Try mistinting the affected areas on a regular schedule for a few week” Rincon-Vitova ‘Marijuana Bio-Control’

Chemical Attack

  • The populations of pests could increase after you use certain insecticides because natural predators may be killed.
  • Protect natural enemies as much as possible by choosing insecticides and miticides that are the least harmful to natural predators. All of the suggested chemicals below are broad spectrum killers, which means they don’t discriminate, they will kill or affect pests as well as predators.
  • When treating for mites, choose the most targeted and specific miticide and alternate it with a miticide of a different chemistry or mode of action to avoid the development of resistance.
  1. Aza Max is good miticide to use. Apply it every 6-10 day to avoid any serious damage from pest.
  2. Neem Oil is good because it sprips the cuticle (outer wax layer) off the most insects, which doesn’t allow them to molt. Does nothing to the eggs so you will need to reapply every 6-10 days.
  3. Pyrethrum is made from some chrysanthemum flowers. They work by exciting the nervous system of insects that touch or eat it. This quickly leads to paralysis and ultimately their death. It’s often mixed with another chemical to increase the effectiveness.

If your growing in containers, you can smear TangleFoot on the rim to help keep crawling pests from migrating from one plant to another. –paraphrasing Jorge Cervantes-

I hope this helps you better understand what your up against if these mites show up in your garden. What you just read is a small amount of the information and research that is out their on the Two Spotted Spider Mite.

Grow Learn Teach

I used many different sources along with some personal knowledge to put this together. Below is a list of those sources.

by Alex Robles Spider mites are one of the most common pests that cannabis growers are going to run into. If they're left unchallenged and allowed to get comfortable they will be devastating to a crop. So instead of doing battle with these little bastards I suggest developing an Integrated Pest Management (IPM) program suited…