Broad mites are almost invisible to the naked eye, making them extremely hard to spot early before the infestation gets out of hand. Before potentially getting the symptoms confused for other plant problems, have a further read to make sure you're dealing with the right pest. This guide takes you through the causes, identification and treatment of broad mites in your cannabis garden.
What Are Broad Mites?
Broad mites (Polyphagotarsonemus latus) are miniscule insects that come from the mite family (Tarsonemidae). They measure between 0.1-0.2mm long, with the males being almost half the size of females. Their bodies are oval shaped and have 8 legs, which can be either a translucent whitish brown, green, or yellow. Broad mites can be found on many types of plant and flower, and commonly on vegetables such as peppers or cucumbers.
As broad mites feed, they suck the nutrition out of the newer growth on the tips of a cannabis plant's branches. As they do this, they leave behind a toxic substance in their saliva which appears as a glossy, glaze or shine, making the plant appear wet.
A broad mite infestation is particularly problematic because it completely stunts the plant and causes damage that takes time to recover from. If the pest is not dealt with as soon as possible, there is a risk of plants not making it to harvest day.
The Causes of Broad Mites
Broad mites live and appear in many gardens in search for food and are trying to survive like any of us. Unfortunately for them, we cannot allow them to continue making their home on our cannabis plants and that means killing off as many of them as we can.
Broad mites do not like the cold and appear most often in moderately warm, tropical climates. They cannot survive when the temperature drops below 10°C or rises above 32°C. This is one of the reasons they can regularly be found feeding and reproducing in greenhouses. A well protected, clean and looked after grow is at less risk than outdoor environments, but if the conditions are favourable there is always a chance.
Identifying Broad Mites
The symptoms of broad mites are most noticeable at the newer growth, where they feed on young plant tissues and lay their eggs underneath the emerging foliage. This causes all sorts of strange deformation and discolouration that make broad mites difficult to diagnose because their damage can resemble that of other common plant problems such as pH imbalances or nutrient deficiencies.
Broad Mite Symptoms In Cannabis Plants:
- Shiny, glossy or 'wet' glaze on the newer leaves
- Twisted, deformed foliage
- Curled or drooping leaf edges
- Bronze or brown patches blistering on leaf tissues
- Stunted growth
- Shorter internodes
- Flowers start turning brown
- Plants eventually wither and die
When eggs begin to accumulate under the leaves they become slightly easier to see, but by this point the infestation is likely to be serious and the plant is likely to already be showing signs of damage. As soon as you detect them, get started with treatment right away. This next section takes a look at how we can get rid of these little critters and stop them ruining our cannabis garden.
Broad mites are similar to russet mites but look different. However, they are equally as destructive and thankfully, we can follow the same treatment procedure.
Tip: Use a 50x loupe or microscope to get a good look at broad mites.
Broad Mite Treatment
It is not easy to completely get rid of a broad mite infestation, but we'll do out best to help you out along the way. Most of the treatments require consistent application until we're seeing healthy new growth and can confirm with a high quality loupe that the mites have been eradicated.
Pruning - Stop the infestation from spreading by removing affected areas. You may have to snip off flowers that are too well developed to treat otherwise the broad mites will continue multiplying there. Bear in mind that you shouldn't apply insecticides or miticides to your maturing buds anyway because the final flavour is likely to be ruined.
In the case that you're in the last weeks of flowering and you discover a broad mite problem, your best bet is to prevent them spreading and save what you can, which may also mean harvesting early to avoid them infecting other plants or multiplying further in your grow space.
Neem Oil - Neem oil is one of those products that helps in almost every pest-related situation. It repels countless different types of predators and that includes broad mites. However, neem oil unlikely to completely get rid of the mites but it does a decent job of keeping the infestation from getting completely out of control.
If you live in an area where mites are common, you may want to consider using neem during vegetation as a preventative spray. For controlling mites, apply as a diluted foliar spray with potassium soap and water and mist every 2-3 days as the lights go off or before the direct light/heat of the day. Apply twice to three times per week for 3-4 weeks after the mites have gone to make sure they don't come back. Best not to apply in the last weeks of flowering.
Insecticidal Soap - Like neem oil, insecticidal soaps (such as potassium soap) are extremely useful in critical situations. Insecticidal soaps are natural and leave no residue. They do need regular application, but there is less chance of damaging your plants like there would be using chemical products.
It is recommended not to spray insecticidal soap late in the last 3-4 weeks of flowering. Potassium soap can be diluted with water and applied as foliar spray once every 2-3 days, making sure to cover the leaves and their undersides. Check the label for strength and dilute accordingly.
Predators may also work to kill broad mites. Video by Fullmeltalchemist from GrowDiaries.
Chemical Insecticides - Unfortunately, sometimes we need to resort to stronger products to get rid of persistent pests like broad mites and other types of mite, like spider mites. These chemical insecticides contain harsh elements that stay in the plant for weeks at a time, and therefore need applying just once or twice to be effective.
Chemical insecticides such as Avid or Forbid work systemically, which means the plant absorbs them and they get consumed by the mites during feeding, eventually killing them. They work well but again, will affect the flavour of your final product if they are used too late into flowering and are sprayed on the buds. Take extra precaution and read the label carefully.
Increasing Temperatures - It is possible to kill broad mites using elevated temperatures. Although this comes with high risk of heavily damaging plants, there may be few options left to try without using chemicals.
If you're adamant about avoiding strong products, you may decide you have nothing to lose by trying this method but consider that it could kill your plant too. Exposing the plant to temperatures above 35-40°C for no more than an hour is the safest way to test it out.
Be even more cautious and expose them for less time if the temperatures are even hotter than that. Alternatively, you could try leaving your plants under the sun on a very hot day for an hour or two.
Tip: Apply sprays during lights out to avoid burning your plants.
Tips For Preventing Broad Mites
Preventing broad mites before they spread heavily is hard because you can barely see them, and less so without the use of a zooming tool. The best way to prevent mites it to keep the proper conditions and monitor your plants everyday.
It sounds simple, but this tends to be how most pest problems are avoided. Saying that, maintaining a grow room requires a lot of work and one slip up could be a reason for broad mites or other pests to move in.
Tips for preventing broad mites:
- Check plants daily and always be on the lookout for pests.
- Keep temperatures between 20-26°C.
- Maintain humidity at 55-60% and lower it gradually throughout flowering to around 45%.
- Circulate the air using oscillating fans.
- Use high quality inline filters.
- Apply routine neem foliar spray once every 7-10 days until the flowering stage.
- Apply neem oil directly on and around the base of the stem to prevent mites climbing back onto the plant.
- Regularly remove any dying foliage.
- Apply treatments to whole grow space and sterilise between grows.
That's all for this one. If you found this article useful or have any further tip or tricks to get rid of broad mites, please let fellow growers know down in the comments section!
External References
Polyphagotarsonemus latus (Banks) (Arachnida: Acari: Tarsonemidae). - Thomas R. Fasulo (retired), Entomology and Nematology Department, University of Florida. (2000). Accessed 21.12.20
Biological control of broad mites (Polyphagotarsonemus latus) with the generalist predator Amblyseius swirskii. - van Maanen, R., Vila, E., Sabelis, M. W., & Janssen, A. (2010).
Host Selection by the Herbivorous Mite Polyphagotarsonemus latus (Acari: Tarsonemidae). Journal of Insect Behavior. - Alagarmalai, Jeyasankar & Grinberg, Mor & Perl-Treves, Rafael & Soroker, Victoria. (2009).
Response of cucumber to the broad mite (Polyphagotarsonemus latus). - Grinberg, M. & Soroker, Victoria & Palevsky, Eric & Shomer, I. & Perl-Treves, Rafael. (2004).
Ecofriendly control approaches for Polyphagotarsonemus latus (Acari: Tarsonemidae) on tea (Camellia sinensis L.). International Journal of Acarology. - Akyazı, Rana & Sekban, Reyhan & Soysal, Mete & Akyol, Duygu & Colee, James & Bostan, Saim. (2018).
This article was updated December 2020.
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