One of the smallest indoor gardening pests, spider mites can also be one of the most devastating to your plants.
Spider mites are not only hard to see with the naked eye, there are also a variety of species within the mite family. The rate at which these bugs reproduce is incredibly fast, making swift action a necessity.
A female spider mite can lay approximately 14,000 eggs in her lifetime. If 50% of the eggs are female, the population could exponentially grow to over 1,000,000 mites in your grow room after 4 weeks if they are not taken care of.
This is why following a grow checklist, and checking your plants thoroughly on a consistent basis is so important.
What causes spider mites to infiltrate plants?
These pests are especially common when growing in soil outdoors. They can be the result of contaminated soil, or in some cases, were on your plants from the start.
This is why buying clones and seeds from the most reputable sources is very important.
Indoors, spider mites can be caused from messy gardening conditions, and non-ideal environment controls. They can also be brought in on your clothing, pets, supplies, and through the air.
We are going to discuss the more sure-fire ways to prevent spider mites from infesting your grow room or garden, but first, let's explain what they actually do.
What do spider mites do to plants?
Spider mites attack your plants by biting into the leaves, penetrating plant cells. They will then suck out the contents, such as chlorophyll. This leads to an array of problems.
Plants use their leaves to release and absorb moisture. When spider mites pierce leaves, plants respond by closing their stomata, as they lose a ton of moisture through these bites. But it is too late, dehydration of the plant will continue to worsen.
An infestation will also lower a plants ability to undergo photosynthesis. As the effects begin to take hold, foliage will start dying and dropping off, before plants die altogether.
Let’s talk about how we can prevent this from occurring in the first place.
Preventing spider mites from infesting your plants
There are a number of ways to protect your garden from spider mites, and a lot of it comes down to a properly sealed ventilation system, and environmental controls.
Step one is not bringing spider mites into your garden yourself. You won’t know you are doing this in some cases, so here are some tips to help you.
Quarantine new plants
Did you recently purchase clones, or were you gifted some sweet genetics from a friend?
I know you are probably excited to start growing, but pump the brakes. You should first set these plants up in a separate room or grow tent, to protect your existing garden.
You can help speed this up by spraying new plants with clean water, and watching closely for signs of pests. Once you are certain they are clean, you can introduce them into the same space as your mature plants.
Keep your growing space clean
A messy growing space is a welcome mat for pests and diseases. Take steps to clean your grow room often. Remove dead plant matter or spills on the floor, and remove any trash promptly.
At the end of each growing cycle, disinfect your entire growing space. This will allow you to start with a clean slate next time you plant.
If you are growing outdoors, there is little you can do to prevent spider mites, as you are growing in their home. However, closely monitoring the surrounding area will do wonders in prevention of an outbreak.
When you do preventative spraying outdoors, consider spraying surrounding plants and foliage as well. This will keep a nice, clean radius and decrease the likelihood that your plants will be a target.
Seal your ventilation system with a HEPA filter
If you are growing indoors, you need to make sure you are constantly exchanging air within the room or tent.
This will keep humidity and temperature levels in the ideal range, which is critical to plant health and pest prevention.
Spider mites can infiltrate your growing space through the air, particularly through your ducting.
If you vent air from a grow room outside, this can be an easy entrance point for these pests.
The best way to combat this is with a HEPA intake filter. These filters are rated incredibly high in particulate filtration, and will do wonders in preventing spider mites and other insects from entering your growing space.
If you want to learn more about grow room environment and ventilation requirements, check out this full guide.
Preventative spraying for spider mites
A more active approach to prevention is spraying clean, cold water on your plant’s foliage. Get the underside of the leaves, as this is a common breeding place for spider mites.
Lowering the pH to around 4 and spraying early in the morning will knock off mites, and deter them from coming back.
A frustrating aspect of growing is that you can do everything right, and still run into pests and diseases. Worry not, because we will show you how to identify spider mites and remove them.
Identifying spider mites in your garden
Part of what makes controlling spider mites so difficult is how hard to detect they are. They are incredibly small, and sometimes can only be seen with a microscope.
Another challenge is that there are three main species of spider mites, and they look and act differe
ntly. We will explain all three species, but there are easier ways to identify spider mites.
Instead of looking for the insects themselves, first look for signs of their existence.
Spider mites create a web like structure on your foliage, but by the time you notice this you will already be dealing with a full blown infestation.
You can also examine the leaves themselves. Look for signs of tiny white, yellow, or orange dots or specks. These are evidence of mites eating at your foliage.
Once you are aware a mite problem may exist, you need to narrow down which species you are dealing with.
What are the different types of spider mites?
By determining which family of mites has taken hold of your plants, you can come up with a better plan of action for eradication.
There are three main types of spider mites found in gardens.
Twospotted Spider Mites (Tetranychus urticae)
The most common spider mite family you will come across are of the Twospotted spider mites. These bugs most often infest hemp, cannabis, and other ornamental and vegetable crops.
Adult females are around 0.4mm long, while males are slightly smaller. They can be recognized by their distinct webbing, which is where they lay perfectly round eggs.
Twospotted spider mites thrive in hot, dry conditions that often occur in the grow room. They can double in population overnight, and usually infest indoor plants by being brought in by growers unintentionally.
They feed on the plant by biting into plant cells, feeding on the contents inside. This will result in leaves showing white specs, eventually turning yellow.
If these mites are not wiped out before flowering, they can work themselves into buds. This will cause issues after harvest while the buds dry, and mites look for food.
Broad Mites (Polyphagotarsonemus latus)
Another common indoor gardening foe, the broad mite is much smaller than its Twospotted cousin. You will not be able to see them without at least 20x magnifcation.
Adult females are half the size of Twospotted at around 0.2mm long. Due to their minuscule size, the best way to identify them is their eggs.
Eggs are perfectly oval shaped, unlike those of the Twospotted mite.
Broad mites are extremely hard to detect until irreversible damage has occurred to leaves. The broad mite has toxic saliva, which causes twisted, hardened, and distorted growth to leaves.
These guys are usually found on new leaves and flowers, as these are freshest. They will stunt growth and kill off bud sites.
Hemp Russet Mites (Aculops cannabicola)
Russet mites, specifically the hemp russet mite, are one of the hardest bugs to get rid of on a plant. They are difficult to control, and cause tons of damage in a short period. They love to feed on hemp and cannabis varieties.
Warm, dry, windless conditions promote rapid growth, and they target these conditions which provide humidity and shelter.
Russet mites are hard to detect, and reproduce rapidly. They can take down a garden before you even have the chance to identify them.
They can enter the grow room via humans, poor soil, or even hitching a ride on other pests. This makes sanitation and sterilization a top priority in infested grow rooms.
Russet mites lay clear, round eggs in the spring. Adults are tiny and wedge shaped, and appear yellow when clustered together. The easiest way to identify these guys is with a microscope. Unlike other mite families, they only have two sets of legs.
Russet mites start their work at the bottom of the plant and work upwards as the population grows. Signs of their presence include yellowing and curling of leaves.
This can sometimes be mistaken as a nutrient deficiency, leading to growers exploring this route. By the time they realize nutrients were not the issue, it is too late.
Look for reduced vigor and overall health of your plants. Early detection of any pest or disease is imperative to eradication.
How to get rid of spider mites
There are a number of ways to combat spider mites once you have identified them, ranging from miticides to actually fighting mites with more mites!
The best plan of attack will depend on how serious your infestation is, whether you want to remain organic, your personal beliefs on pesticides, and more.
What is the best treatment for spider mites?
Miticides are very effective against spider mites, but choosing the right one and using it correctly is tricky. With some general guidelines, these will be your best weapon against spider mites.
We recommend using contact sprays instead of systemic sprays. This is because contact sprays stay on the foliage surface, whereas systemic sprays enter the living tissue of plants.
Contact Miticide Sprays
As the name suggests, contact sprays need to come in direct contact with the target pest. Apply liberally, completely covering larvae and eggs. You will need multiple applications over a few-week period.
Try rotating between a couple products every few days while spraying, to prevent the spider mites from developing a resistance to a certain pesticide.
The best time to spray your plants with oil based pesticides is right as lights are about to turn off. Try and turn them off manually 15-20 minutes before you normally would, giving you enough time to spray your garden in low light before the plants need to be in darkness for the night.
Systemic Miticide Sprays
Systemic products sold as miticides should never be used for consumable plants such as hemp or cannabis. These chemicals will live within the plant, and when you consume your harvest, you will be consuming these sprays.
Using Predatory Insects To Fight Spider Mites
A common pest control practice is fighting fire with fire - or other insects. Those who do not want to spray anything on their plants can use a number of beneficial bugs to eat away at their infestation.
While it may sound crazy to release additional bugs or mites into your garden, there is a science behind this.
Ladybugs are a useful, human-friendly tool for mite eradication. Ladybugs will eat away at mites on your foliage, and will stay on your plants until the food is gone.
Predatory mites will go out and eat other spider mites without harming your plants.
Phytoseiulus Persimilis predatory mites’ diets consist solely of other spider mites. They will eat so fast they end up starving and dying once they consume all the problem mites.
When using predatory mites, be careful about spraying your plants with pesticides.
You don’t want to kill off the bugs that are supposed to be helping you. These two methods can be used together, but timing is important.
Spray your plants up until you introduce predatory insects. Once you implement them, stop spraying.
How to apply miticides in the garden
Here are some of the products we recommend for fighting spider mites, with their recommended application rates.
General Hydroponics AzaMax: Low end: 2 tsp / gallon, Mid end: 2 Tbsp / gallon, High end: 4 Tbsp / gallon
General Hydroponics Exile: 5 Tbsp / gallon
*do not mix sulfur or use within 3 days of spraying/burning sulfur
General Hydroponics Prevasyn: 1 - 2 tsp / 1 Gallon
*Every 4-7 days
Pyganic Gardening 1.4%:1-2 oz / gallon
Pyganic Specialty 5%: .25-.5 oz / gallon
Mighty Wash: Ready to Use, DO NOT DILUTE
Green Cleaner: 0.5 - 2 oz / 1 Gallon
SNS217 : Ready to Use, DO NOT DILUTE
Fox Farm Force of Nature :1.5 oz / gallon
If you follow the steps outlined here, you should be able to prevent, identify, and remove spider mites should the time come. These are just one of many common indoor gardening pests.
To be sure you are fully prepared for whatever you come across, check out our full guide on common grow room pests and diseases.
If you want help battling spider mites, and are unsure which course of action you should take, you are not alone. Our expert growing staff is available at 888-815-9763.