Spider Mites, Russet Mites and Bulb Mites
As a grower you learn to take precautions against the various pests and nasty things that would love to make a meal out of your plants. Yet even the most conscientious of gardeners will likely find themselves in a protracted battle with spider mites, russet mites or even bulb mites at some point. Having the knowledge and tools at hand to deal with an issue right away can make a big difference in how long your fight lasts and how far you will need to go to emerge the victor. First, you will need to Know Your Enemy.
While spider mite adults and eggs are very small (<1mm), they can be seen by the naked eye and tend to live and lay eggs on the underside of leaves. They may be white, brown or red in color.
Spider mites are most easily identified by the small spots they leave on leaves as they feed. However by the time spotting is easily seen, mites may be well established.
As mites successfully colonize leaves they will spin webs in and around them to protect and allow access to other parts of the plant.
While russet mites are typically less common than spider mites, their numbers have been on the rise as of late. They are smaller and much more difficult to identify.
Keep a close eye out for curled, clawed and distorted leaves. Larvae bloom will look like rust.
Check them with at least a 60x scope to rule out russet mites as a cause of the damage versus a pH or nutrient issues.
By the time leaves start to turn brown and crispy the russet mites may be too numerous to fully eradicate.
Bulb mites won’t hesitate to settle into the root zone of your indoor plants, leaving you with few choices. Drenches are often necessary to knock them out before they interfere too much with the plant’s development.
As the mites interfere with nutrient delivery the leaves may appear droopy and pale, as if over watered.
They are similar in size to spider mites, but have four pairs of legs, are typically pale in color and look like a light bulb.
Spider mites thrive wherever it’s hot, dry and dusty. Discarded leaves, unswept floors, uncirculated air, and dry root zones are all an open invitation for a spider mite infestation.
Eggs can easily hitch a ride on hair, skin, clothes or even an air current. So mites can spread even when infected plants are quarantined. Eggs hatch more quickly as temperatures rise, in as little as three days at 80 F.
Russet mites tend to prefer similar warm, dry conditions. They are often most problematic during the summer. However, they can be active year-round. As they are even smaller than spider mites, they often go undetected.
Despite their name, bulb mites feed on a wide variety of plants, including Cannabis. They live in the root zone of plants rather than inhabiting the stems and branches. Again, they reproduce more quickly with warmer temperatures.
There is evidence that bulb mites are more attracted to plants infected with a fungus like fusarium, so avoid over watering and root rot.
Feeding and Behavior
Spider mites pierce the undersides of leaves to suck nutrients cell by cell. The scarring from this cell death is what causes the pale spotting on leaves, while the darker specks are frass (fecal matter).
Adults can lay hundreds of eggs over the course of several days, so even minor mite damage must be closely and frequently monitored. As mites continue to feed on a leaf, it will become pale
Russet mites are usually not visible unless they are present in great numbers, when they clump together and can look like a pale dust. Like spider mites, they will also feed on leaves and leaflets. However, petioles (leaf stems), fruit flowers and even glandular trichomes are on the menu as well. Thus, it is imperative to have them controlled before fruiting or flowering begins.
Look for underdeveloped new growth, drooping, leathery leaves, and curled or crispy leaf edges. It is very easy to mistake the damage for a deficiency or simply over watering.
Since bulb mites live within and feed on the root zone, their damage can very easily look like a deficiency. Leaves will turn pale, and the plant will begin to look underfed. Verify bulb mite presence with a loupe or scope before you begin adding nutrients or new supplements.
Prevention and Control
Developing good habits in the grow room will go a long way. Below are some of the most important areas to focus on when trying to prevent or control a mite outbreak.
It bears repeating, eliminating dust and debris is crucial to denying mites purchase in your garden. It is also the easiest thing to let slide when life inevitably interrupts your garden time. However, it is worthwhile to make cleanliness a top priority.
Since mites like hot and dry climates, keeping the garden cool and moist can help slow their reproductive cycle, giving you time to deal with an outbreak. Proper ventilation and humidifiers can help accomplish this with indoor plants.
Hitch hikers from the veggie garden
Mites feed on a wide variety of plant types and species. Even if you don’t see any signs of them in your garden, always play it safe. Shower and change clothes if you’ve been working in your outside garden before entering your indoor garden or greenhouse.
Be exceedingly careful when accepting outside clones into your garden. Grow from seed when possible if seeking new genetics. Always quarantine, even if they are from a “trusted” source. See if you can check out the garden and mother plant(s) the clones are coming from before you take them home.
If you have identified mites in your garden, stay on top of manually removing damaged leaves to help keep populations in check. A garden hose can be very effective at knocking mites, eggs and webs from a plant even though it doesn’t kill them directly.
This can also help keep mites at bay, making it more difficult for them to start building and maintaining webbing when the leaves and stems are in motion.
Foliar Spray Regularly while in Veg
A foliar spray of Silica and Kelp will help strengthen plants and make it more difficult for mites to get a foothold, while also helping to keep humidity levels up. Watch out for powdery mildew when increasing RH levels.
Natural and Organic Treatments
Keep in mind that no single treatment you choose, organic or otherwise, is likely to be enough to get rid of mites. You may need to select several compatible methods and rotate or use them in conjunction. The winning combination in my garden was Azamax, and alternating foliar sprays of insecticidal soap and an essential oil based spray. Don’t get discouraged if something doesn’t seem to work. Persistence pays off against mites.
Alcohol kills adult mites on contact and evaporates quickly, so plants tolerate it well. Mix half Isopropyl Alcohol with half water and use as a spot spray.
Predatory insects like Ladybugs can quickly put a large dent in mite populations. Lady bugs are one of the few controls that are completely safe for your plants all the way through flowering.
Introduce them anywhere you notice mites or mite damage, and introduce more ladybugs as needed to maintain their population for at least 2 weeks. When introducing lady bugs lightly spray them with sugar water to provide them with energy and keep them from flying away. If using lady bugs indoors, remember to occasionally spray them with water to keep them hydrated.
Insecticidal Soaps and Oils
While not a pesticide, they are very effective since control mites and insects in various ways simultaneously. Soaps and oils interfere with breathing and metabolism, and are also disruptive to cell membranes. Natural oil based products like Green Cleaner and Castille Soap work by suffocating pests and eggs so there is no way for them to build a resistance. Plants generally tolerate soaps and oils well, but keep an eye out for burned or scorched looking leaves and adjust accordingly. Spray the top of your growing media, plant stems, the underside and tops of leaves until saturated.
Neem deserves a special mention because of it’s active ingredient, Azadirachtin. Azadirachtin acts as both a repellant and an antifeedant. A dunk can be prepared for small plants, and a root drench or foliar spray for larger plants Several applications will be necessary to treat the adult populations as they hatch. However, if too many adults survive treatment and are able to reproduce, spider mites can become resistant over time.
These are extracted from neem so that there can be better control over formulation and dosing. Azamax is a popular brand. It can be applied as a foliar spray or root drench. This allows Azadirachtin to act as a systemic pesticide. Although it’s not very toxic to humans, always follow the manufacturers instructions carefully when applying any pesticide, organic or not.
Sourced from bacteria, this miticide acts on the nervous system paralyzing mites. It is approved for use on food crops, but should still be applied with great care and caution to avoid irritation or over-exposure. This should be a last choice effort.
Originally derived from chrysanthemum flowers and effective against a wide range of pests, organic and synthetic pyrethrins account for many of the pesticides on the shelf today. While they will kill mites and eggs on contact, it is important to get full coverage and use at the appropriate strength and interval to prevent mites from building a resistance. Plants typically tolerate them well, but too much can cause leaves to brown and wither.
Spinosad and Spinosyn A
Another bacterial derived insecticide, Spinosad acts on contact or ingestion to inhibit neuron function in insects. However, it is safe for people and pets. Even small doses can be lethal to honey bees, so use extreme caution when applying outdoors.
Capsaicin and essential oils
Rosemary essential oil and capsaicin kills mites on contact, and is gentler on plants than some of the other foliar sprays included on this list. It can also be a good alternate or spot spray.
The Big Guns: Systemic Miticides, Foggers and Bombs
For particularly stubborn mites that shrug off organic pesticides and barely seem bothered by natural methods, it may be necessary to use a chemical miticide or whole area treatment to eliminate the issue. Before you take this step please carefully consider your safety and do your own research to make sure you fully understand the risks and necessary precautions. Most of these substances will require full protective clothing including gloves, goggles and a respirator. Many are listed for use on ornamental plants only. Please also take into consideration how long these chemicals will last in your plants. Consider whether it may be safer and more expedient to cull badly infested plants.
The active chemical in Forbid 4F blocks fat synthesis in mites causing them to dry out. This is similar to how potassium fats in insecticidal soap work. Forbid is not a systemic pesticide. However it is absorbed by the plants leaves so full saturation is not as critical.
This pesticide kills on contact and lasts 21 days. It should never be used past the vegetative cycle. Floromite SC‘s downside is that if mites are not wiped out with the initial application, they will have several generations to develop resistance from a single application.
These are synthetic versions of Pyrethrin. Unlike their organic counterpart they tend to linger in the environment, and are more toxic to humans and animals if inhaled or absorbed through the skin. Total Release foggers often use pyrethroids as their active ingredient
Other Systemics, Acephate
These are found in products like Bonide System Insect Control. They work much like an insecticidal soap, but linger within plant tissue for around five days continually killing adults.
A note/warning about “Hot Shot Pest Strips”
These are only mentioned because there have been a number of growers misusing them to control their spider mites. These strips of plastic are impregnated with a chemical Dichlrovos (DDVP), which is slowly released and kills most varieties of insects and arachnids once concentrations accumulate. Essentially, they act a lot like a fogger, but are slower and work over a much longer period of time. Unfortunately, DDVP is also toxic to humans and pets. Being colorless, odorless and active for many months, it is potentially quite hazardous to use for an environment like a grow room that is difficult to seal and requires constant upkeep.
Once you have started to turn the tide it is easy to think you’ve won, get complacent and stop checking for damage. There is no silver bullet remedy to mite mitigation. Develop your own routine and stick with your plan. Check plants for changes daily and prune damaged foliage. Don’t haphazardly bounce between treatments, but be ready to change your approach if you’ve confirmed that the correctly applied treatment(s) have yielded resistant mites. If you do alter your normal growing environment to make it less hospitable for mites during an outbreak, don’t forget to take precautions against other issues like powdery mildew and bud rot. Try to at least get mites under control before beginning to flower, since your options become much more limited especially once flowers begin to develop.
If you have a product that has worked remarkably well for you, a great home brew organic bug juice recipe or any comments/corrections, comment below!