How to spot mould in your weed

You do not have to be a Cannabis Expert to know that you have purchased a low-quality product after looking at hay-smelling, tiny brown buds in your jar.

However, while some quality flaws may be easy to detect, other, more severe issues that can creep into your weed even though it may look alright. These problems fall under the umbrella of possible undesirables in cannabis and it takes a bit more training and specific tools to spot them. 

This article will show you examples of the undesirables found in the Canadian cannabis industry and prepare you for detecting them in the future. But first, let’s look at the tools that will help you to spot these flaws.

Magnifying loops are used for evaluating cannabis. Cheap budtender option.

Magnifier Loupe

A magnifier loupe is a great starting point for anyone wanting to investigate their cannabis more in-depth.

This tool is excellent for getting a vague overview of the trichomes’ density and ripeness. The loupe on the Urbanistic shop offers a LED light and a 40x magnification for a more detailed observation of your flowers. 

It also can be used for inspecting small, white areas on the bud that could indicate jar rot or powdery mildew.

Digital Microscope

The professional instrument of every highly sophisticated cannabis reviewer.

Different than the magnifier loupe, our digital microscope offers a magnification of up to 2000 times, allowing you to get deep insights into your trichomes and spot undesirables like mould or powdery mildew more efficiently. 

Besides, the digital microscope also allows you to view and capture 4032x3024 photos of your investigations on its 7inch HD screen. You can then share these pictures on your Social Media page or send them directly to the Licensed Producers if you find any undesirables in your cannabis. 

Now that you are familiar with these tools let’s look at some undesirables and how you can detect them.


Believe it or not, jar rot and powdery mildew are moulds that have been found quite frequently in the recreational cannabis industry here in Canada.

Those who find these undesirables become quite concerned as these moulds can contain poisonous chemical components called mycotoxins. According to the article Mycotoxin Analysis in Cannabis written by Eric Janusson, Et al., inhaling mycotoxin-contaminated material can result in pulmonary emphysema and lung cancer.

Usually, when there were issues with undesirables in products, the Licensed Producers (LPs) connect with the BCLDB (or other provincial distributors) to announce a recall under “News and Updates” on their online Store’s homepage and/or other social media platforms.

British Columbia Cannabis Store. Report issues with your Canadian Cannabis products through provincial governments.

While consumers do appreciate producers owning up to their flaws by recalling their products, recently there have been speculations circling. Connoisseur and consumers have begun speaking out about how some LPs do not seem to act promptly to remove said products from the market.

And, since not everyone is inspecting their products as closely as we teach you here, one may assume that many consumers are unknowingly being exposed to these moulds.

One reason why it is difficult to find these flaws visually without using a microscope is that they are both microscopic and white in colour. Many people become confused by these undesirables as white, tiny Trichomes on your bud. But, different than trichomes, jar rot and powdery mildew are usually in a cluster on sporadic areas of your bud rather than all over your flowers. 

So, when starting to observe the flowers with only your eyes, watch out for larger, whitely covered areas and then observe these more closely with your microscope.

Jar rot in cannabis found with magnifying loop and digital microscope. Be a conscious consumer.

Jar Rot

Jar rot is the same type of stringy, white/greyish mould that you can also observe on rotten fruit or vegetables.

It usually develops on overly moist buds that were improperly packaged or cured, causing the flowers to get mouldy while the product was shipped and put onto the shelves. 

Since Jar Rot is odourless, the only way to detect it is by observing your buds very closely and looking out for areas that are densely covered with stringy white hairs instead of bulbous trichomes. 

Once you identified an area that looks suspicious, take your microscope and start observing it more deeply. Under magnification, Jar Rot looks like thin, stringy spider webs so if that is what you noticed, make sure to snap a picture of it and reach directly out to the LP and retailer you purchased from to make them aware of this issue. By contacting both the retailer and LP, you will (hopefully) be helping other consumers avoid undesirables and initiate a fast-moving product recall.

Cannabis inspection report by expert and cannabis sommelier. Purchase on Urbanistic e-commerce marketplace now.

Powdery Mildew

Just like Jar Rot, Powdery Mildew is a kind of odorless mould that appears as a white cluster on your buds. But, other than Jar Rot, Powdery Mildew usually invests your cannabis during the flower cycle of the growing process. 

Since powdery mildew is a common mould found in most gardens, the grow-ups usually get invested when a grower was exposed to their spores outside and carries them on their clothes into the facility.

That is one of the reasons why you usually see everyone in a licensed facility wear Personal Protective Equipment (PPE) instead of normal, outdoor worn clothing.

Under the microscope, Powdery Mildew does not look stringy like Jar Rot, instead, it appears as a flakey white powder that covers parts of your bud.

Mould examples found on plant life.

Powdery mildew on a sunflower. 


Mildew found on cannabis should not be consumed. Purchase microscopes at the best price on Urbanistic. Available in Canada and United Kingdom.

Powdery Mildew on a cannabis flower.


Bugs are usually rare to find in the legal cannabis market. That being said, it can happen. In some instances, producers can not get rid of their biological pesticides or had plants that were infested with spider mites or thrips. 

Insects are the easiest to detect in your cannabis, especially when using a digital microscope. They usually stand out from the trichomes and plant material through their shape and brown or yellow colour. 

If you look closely at your flowers and recognize dark brown or yellow little spots on them, you should grab your microscope and magnify the buds in these areas. Now it should be easy for you to tell if there is a bug in your weed, as you will notice the shape and colouration of their bodies.

Lastly, if you'd like to deepen your knowledge about cannabis and its undesirables, we recommend you to have a look at our Cannabis Microscopy course, which will not only teach you how to look for undesirables in your cannabis, but you'll also learn all about the world of trichomes.

This industry needs your deep observations

Even though cannabis is regulated by a governing body, there is still the possibility of undesirables being present. However, no one should ever be smoking any mouldy or bug-infested products, and let’s not forget, cannabis is first and foremost a plant.

For that reason, it is so important to properly check the products to avoid consuming undesirables. And, if you do find unwanted elements, inform the Licensed producers to keep them accountable. 

That is why you should invest in a cannabis microscope to (1) spot these flaws, (2) write down the LOT number of the product, and then (3) make the producers and their customers aware of them. 

If we collectively start observing our cannabis more deeply and voice our concerns, we can create a safer environment for consumers by minimizing the number of faulty products on the market.


  • Eric Janusson, Ph.D. Ali Wasti, and Markus Roggen, Ph.D., 2021, Mycotoxin Analysis in Cannabis, Terpenes and Testing Magazine, accessed 9 January, 2022,
  • Max Montrose, 2020, What is Jar Rot?, Trichome Institute, accessed 9 January, 2022,
  • Max Montrose, 'Part 6: Evaluating Unacceptable Visual Characteristics', in Interpening, ed. by Amy Thomas, (Trichome Institute 2021), pp. 59-77 (pp. 68-74)

Tom Rothmeier Bio