Contamination is a devastating problem in mushroom cultivation. Besides, we, as humans, animals, and especially insects, can spread disease. In this article, I will provide you with tools and tactics to first prevent contamination happening, and second to cover if it already happened.
These tools range from cheap and easy up to more advanced and a bit more expensive. There comes no priority with this list. Pick one tool or tactic and apply it. Add more to your arsenal along the way.
Improper sterilization is the leading cause of contaminated substrate and pests. Reasons for that can be found for example in
- A short sterilization process
- Low temperature during the sterilization process
- To dense packaging of the substrate blocks
These factors are especially true is you are just starting out. But I realized during my research and discussions that even seasoned mushroom farmers make mistakes on the way. To give you a jump start, I put some great information about sterilization together in my article How Your Sterilization Method Will Impact Your Mushroom Yield.
While we need in certain phases for the cultivation of mushrooms fresh air. With it comes the risk of contamination. It is, therefore, a good practice to filter the incoming air (Figure 1) and outgoing air. The filter prevents a) insects and contamination from coming into the room, and b) disease spreading by filtering before going through the exhaust.
While many mushroom farmers pay attention to the incoming air. Only a fraction of them will filter their exhaust air. Depending on your farm design, this can increase the risk of pests.
Keep the air inside your room fresh, clean, and according to the dedicated needs for each room. This will lower the risk of pests.
Check on a regular schedule if your systems are running correctly.
A well-insulated room keeps pests outside. Use, for example, urethane to seal all gaps and openings inside the room. This approach is recommended for your laboratory because every pest which enters your lab will multiply throughout the transfers.
Another good way to prevent insects and animals from coming into your rooms is to install double doors (Figure 2). For your laboratory, you can even combine this system with overpressure (point 6) and sticky mats (point 7) to even lower the risk.
Figure 2: Basic principle of a double door
A good practice is to install within the entrance area (Figure 3, blue area) a sink and a place where you store clothes (shoes, jackets, masks, gloves, scalpels, …). You, therefore, can change your clothes and clean your hands before entering the room. This prevents further contamination from entering the room.
Figure 3: Basic principle of a double door with cupboard and sink
By putting more air into the room than air can leave it, we can generate overpressure. This overpressure prevents insects and contamination from entering the room.
If you want to achieve overpressure, you have to install a blower (Figure 4) into the room.
The get the right blower you have to check the specification sheet (Figure 5). In it, you will find the airflow rate per minute (Figure 5: here, CFM 131).
Figure 5: Example of a specification sheet of a blower
You then have to calculate the air volume of the room.
Example: 2.5m x 1.5m x 2.0m
For people outside the US who are using m³/min instead of cfm we have to convert this number. If we do that, we will end up with 3.71 m³/min (1 ft = 30.48 cm; 1f² = 30.48³ = 28,316cm³; 1cm³ = 10^-6m³; 28,316/10^6 = 0.028 m³; 131 x 0.028 = 3.71 m³/min).
With this number (3.71 m³/min) we can now calculate how often the air inside the room will be exchanged.
The air inside our room will be exchanged every two minutes if we run the blower at the maximum power.
To reach overpressure, we do not have to do this. We, therefore, can reduce the blower and save energy. But how much can we reduce power?
To calculate the necessary power, we use the blower door test. Here a room will be pressured with air (+ 50 Pa), and then the leakage rate measured. The values for the recommended leakage rate vary between okay with < 3/h (0.05 m³/min) and very good with < 1/hour (0.02 m³/min). Which means that our flow rate should lie above these values.
Because of the difference between our blower (3.71 m³/min) and the leakage rate (0.05 m³/min), we have several options.
- We install a smaller version of the blower.
- We install a HEPA filter which will lower the airflow.
- We blow air not only into the entrance area (Figure 6, blue) but also into the main room itself (Figure 6, green area).
Figure 6: Example of a room with double door system.
As already mentioned, sticky mats (Figure 7) are an excellent way to keep insects and contamination outside of your room. Install them, for example, in the entrance area of your lab. Depending on which type of sticky mat you are buying, you can remove from time to time a layer and, therefore, have a clean surface again. Or you just clean the sticky mats accordingly to the instructions.
If you do not clean it or remove the top layer regularly than remove the sticky mat at all because a dirty, sticky mat is riskier than no sticky mat at all.
Do not place a sticky mat into your fruiting rooms. The high humidity does not work well with them.
Flyscreens are another excellent way to reduce the number of insects that will enter your room. Install them in frames (Figure 8), windows (Figure 9), and your air intake/exhaust. Check them regularly for holes.
To reduce the number of insects especially flies inside a room, you can install fly stripes (Figure 10). They are cheap and easy to install. Check them frequently to get an idea of the contamination level. If you have to change them to often, then you should start looking for the root cause.
Do not place a fly strip into your fruiting rooms. The high humidity does not work well with them.
Besides fly stripes, you can use the good old recipes from grandma. Just add for example
- vinegar and dish soap or
- sugar and water or
- honey and water
in a jar and place it into your room (Figure 11). Place a funnel over the jar, and you are good to go. Check them frequently to get an idea of the contamination level.
Figure 11: Example of a homemade fly trap
If you want to use a more advanced version, you can install a light trap (Figure 12). In this case, the UV light is attracting the flies. They will be killed when they hit the high voltage grid. Check them frequently to get an idea of the contamination level.
Do not place a light trap into your fruiting rooms. The high humidity does not work well with them (electricity!!).
Staff and equipment control
You read it correctly. In order to avoid pests from spreading, you have to make sure that your staff and you as well only move from clean to dirty areas and not the other way around.
Someone who must deal with contaminated bags should not work on the same day in other areas, except the person can take a shower and change the clothes. If you think you can wait after you finished the clean work, then you are risking that the contamination gets spread.
Do not bring equipment from dirty areas into clean areas. Color-code your equipment accordingly its area.
Next on the list to prevent and to spread contamination and pests is to sanitize every equipment and room properly. Use alcohol or a mixture of alcohol and water or hydrogen peroxide (5%). Follow a strict regime.
Depending on your farm design, do not forget to clean the floors.
Sanitize everything from time to time what you touch with bare hands (e.g., doorknobs).
Reduce crop cycles
The longer you keep your substrate inside your fruiting room, the more likely it is that you run at some point or another into a pest problem. In reducing the total time inside the fruiting room pest organisms that could enter the room have not sufficient time to reach economically harmful levels within the crop.
Hand in hand with sanitation goes the turnover of a fruiting room. Each room should be adequately cleaned and dried before sanitized. This prevents the sanitizer from becoming ineffective. Some companies are letting run UV light for a specific amount of time.
Spent mushroom substrate
If you are using or want to use your spent mushroom substrate on your farm (e.g., casing), then you should sterilize it properly. Because otherwise, it will be a root cause for pests on your farm.
The longer the operation is running, the more likely it is that it will run into a pest problem. This is especially true for old fruiting rooms. Every time you are turnover a room, clean and sanitize it bacteria, viruses, and so on will develop resistance to this process, or you just go every time a little bit lazier.
Over time this adds up. You will notice that, for example, when the number of pests is increasing over the year in one room.
If this happens, then it is time to deconstruct the room and build a new one. But not on the same spot.
Check and balance
One of the best methods to prevent pest from spreading is to identify it at the beginning. To achieve that you should check on a regular schedule your farm for indicators. These indicators might include things like
- Fly stripes
- Holes in the fly screens
- Number of contaminated bags per day/week/fruiting room
- Appearance of flies
- Appearance of blotch
- Cracks in the construction
This means that you should dedicate a certain amount of time per day, week, month towards pest control. Plan this time upfront and schedule it accordingly. Only if you put it onto your calendar, you will do it.
With these strategies, tactics, and tools you will address the vectors of contamination. If you want to learn more about these vectors you will find more in my article How Do I Prevent Contamination?
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