Pests, Diseases and Troubleshooting

Pests, Diseases and Troubleshooting

There are many problems that can happen to the home cultivator. We have environmental problems. Then we have a range of pests and diseases that love our mushrooms as much as we do. It’s not always easy to determine exactly what the problem is either, since a single problem can have many manifestations. As with a vegetable garden, vigilance and active response are two important parts of the puzzle. Planning, as we do in integrated pest management, is another important part. There are things we can do to save ourselves much headache before it happens, as well as things we can do to solve a problem once it appears. Problem identification and management is the subject of this lesson.

Problem Identification and Management

Generally, mushroom cultivation concerns four factors: temperature, light, humidity, and carbon dioxide (CO2). These are the factors that need to be monitored and controlled. Too hot, and the fungi won’t fruit. Too cold, they’ll die. While most fungi don’t photosynthesize, they are photosensitive, meaning they do notice and react to the light. Most mushrooms in cultivation do need some ambient or indirect lighting. Lastly, too much CO2, which is a natural byproduct of respiration, and the fungi won’t fruit. Too much humidity invites parasitic bacteria and fungi, too little and the fruits will abort if they form at all.

Creating the best conditions possible in your grow space will save a great many headaches. Martha tents are very popular and easy to set up. They’ll create a fairly clean space where temperature and humidity can be kept within a desired range. Mine cost me $150 to set up but it’s been well worth the effort! In my area, winter indoor air is very dry even with a humidifier. Temperatures outside affect temperatures indoors. When it’s -30 outside it’s cold everywhere, and fungi will often die if not kept warm. A standard heat mat can help if your indoor temperatures fall into the 30-40s.

Fungi do need a fairly high humidity, around 90%, but 100% yields constantly wet caps and substrate that are an invitation to molds, Verticillium, and flies. Temperature and humidity controllers keep both parameters within desired ranges. A fan keeps fresh air circulating and removes both CO2 and excess moisture, but keep in mind that fresh air also contains spores from various undesirables. A filter is really helpful here. Closing off the environment as much as possible reduces contamination vectors. Please reference the Contamination lesson for more information on contamination and sterile technique.

Pests and Diseases


When it comes to flies (most commonly Sciarid and Phorid) and other insects such as fungus gnats, there are a variety of ways to deal with them. I’m not a huge fan of chemicals, but fly paper is fairly common. Stamets uses tree frogs in his grow room. Since I also grow carnivorous plants, a couple of them in my grow room does wonders to reduce populations of house flies and fungus gnats. There are also biopesticides, most notably a parasitic nematode (Steinernema feltia) and Bacillus thuringiensis, aka BT-14. Both are available for home use as of this writing.

Contamination and Invasion

Green mold, aka Aspergillus, Penicillium or Trichoderma are all too common in the home mushroom garden. This is always a sign of contamination, whether from bad culture, improper pasteurization or sterilization, air borne, insect borne, even cultivator borne. Sterile techniques are paramount in prevention. Contaminated cultures, spawn, blocks, etc should be removed and disposed of. While you may be able to save your culture if it’s far enough away from the mold, the safest thing to do is throw it out and start over.

Verticillium aka brown spot aka dry bubble is also a fungus and causes light brown, irregular, superficial spots on the caps of the mushroom. There can also be small dead areas on the cap. Severe attacks can cause abnormal swelling of the stalk and deformed growth & subsequent shriveling of the fruit. This is best controlled through sanitation. Fungicides aren’t the best choice since mushrooms are fungi, and therefore sensitive to these chemicals.

Turkey tail invasion: this is actually an edible mushroom with many benefits of its own, but left to its own devices it’ll invade your logs and crowd out the mycelia you’re trying to grow. Quick inoculation and wax over the drill holes are keys to stopping it. If it’s too late and the conquest is complete, I suggest eating what Nature gives. While not the tastiest mushroom in your cupboard, it’s not known to be toxic, at least not as of this writing. It does have both anti-cancer and immune-boosting benefits.

Bad spawn/culture/mycelium: Somewhere along the line, your culture got contaminated. The only way to know this is to try growing it, unfortunately. I’ve had this happen and the only thing that can be done is to toss the culture. Prevention is to buy only from reputable sellers.


Be aware that woodpeckers and insects love to chew the wax off of the logs, and they also love your mushrooms. Squirrels, chipmunks, and even deer love your mushrooms too. You can try putting your logs on landscape cloth for the bugs, or fencing in the case of critters. Basically, you want to deny access. Check local regulations before using a pellet gun or 10/22. Many municipalities have ordinances regarding firearm discharges within their fiefdom.

Additionally, there may be regulations governing disposal of the dead bodies. Slugs and snails also love mushrooms. Again, denial of access is the key to control. Elevation of your logs is helpful. There are slug control products on the market but be very careful to select one with the most narrow target range possible, otherwise you risk killing beneficial insects as well.

Dactylium diseases, aka Cobweb disease. Dactylium cladobotryum

Characteristic symptoms are a white cobweb-like growth appearing on the casing and spreading over the surface. Upon contact with a sporophore, it causes a wet brown rot that can extend throughout the crop, causing total crop loss. This is primarily a disease of the button mushroom, Agaricus. If spores become airborne they can spread to the entire crop. Control via salt application, while effective, can cause the dry spores to become airborne. Careful adherence to the correct process is mandatory to prevent this spread. Chemical control is Prochloraz, brand name Sportak.


Martha Tents

  • Skinny stems/fruit bodies or coral-like growth: CO2 levels might be too high
  • Fuzzy stems: could be too much CO2 or moisture
  • Caps brown/cracked: could be not enough humidity or harvested too late
  • Growth stops after pinning: possible low or temporary drop in humidity
  • Fruiting bodies pale: high temps or low light environment
  • No growth at all: possible high temps, substrate not fully colonized or too dry

Straw Culture

  • Green/black molds appearing: insufficient pasteurization, prolonged CO2 levels, incubation temperature too high. Lower CO2 levels via increased air exchange. Lower incubation temperatures. Pasteurize completely.
  • Mushrooms fail to form: bad strain, chlorinated or contaminated water, or incorrect initiation strategy. Obtain strain from reputable sellers, use only filtered or distilled water, investigate and correct environmental conditions.
  • Mushrooms abort: mites, nematodes, or insect larva damage. Humidity too low.

Supplemented Sawdust

  • Mycelia fails to colonize within two weeks: bags inoculated while too hot, mycelia/wood type mismatch, over-sterilized or not enough moisture. Check temperatures, as too low temps can slow colonization.
  • Mycelia stops growing, accompanied by molds, foul odors, and slimy fluids: inadequate sterilization, contamination introduced along the process, bags not separated to allow heat loss or excessive CO2 during incubation.

Grain Culture

  • Grain contaminates before opening or inoculation: bacteria in grain beforehand or entered during cool down. Sterilize completely; leave in canner until ready for use. Soak grain overnight to make more susceptible to sterilization and inoculation.
  • Mycelia does not grow: too dry or bacterial contamination, or culture doesn’t like the media formula. Remember balance: dry but not too dry, sterilize thoroughly, or alter media formula
  • Mycelia grows spottily or incompletely: insufficient distribution throughout grain. Shake more often. Insufficient inoculation rate. Use more culture during inoculation.
  • Overall failure to produce mushrooms: unsuitable environmental conditions, ie humidity too low or CO2 too high. Correct conditions. Chemical contamination, ie solvents, chlorine. Remove toxins.


This lesson has covered some of the more common diseases and pest encountered in home mushroom cultivation. Many diseases, such as brown rot and cobweb disease, are fairly host-specific. This is why a good reference is essential! Identification involves careful observation and a lot of detective work. Documentation is also helpful; record your observations carefully, take pictures, and do some research to piece together the entire puzzle. Only when you know exactly what you’re dealing with can you treat it properly. As always, sterile technique first and foremost will save you a great many problems. Good luck on your journey!

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