Reference/Contamination

Every grower deals with contamination eventually. This page helps you work out what you're looking at and whether anything can be saved.

When in doubt, throw it out. A doubtful jar is rarely worth risking the rest of your grow over. And never open a contaminated container indoors. Bag it sealed and dispose of it outside; opening it releases millions of spores into the room where you do your clean work.

Not contamination

Plenty of normal things look alarming the first time. Check these before throwing anything out.

What you see	What it is
Yellow or amber droplets on the mycelium, no smell	Metabolites (exudate). The mycelium is pushing out excess water and byproducts. Often a sign of stress, but not contamination.
Blue or bluish-green staining where mycelium touches the jar or tub, or where it's been handled	Bruising in species that stain blue. Test: rub it gently with a cotton swab. Mold leaves powder on the swab; bruising doesn't.
Fluffy, cottony white patches	Tomentose growth or aerial mycelium, usually from high humidity or CO₂. Still white and still yours.
Dense white knots	Hyphal knots: the very first stage of pins.

Molds

Trichoderma (green mold)

• Looks like: starts as fast, dense, bright white growth, then turns emerald or forest green, usually in a ring or patch.
• Where: bulk substrate, grain, agar. The most common serious contaminant.
• Cause: its spores are in almost every soil. They get in through poor sterile technique, under-pasteurized substrate, or open air.
• What to do: toss it. Trich spreads quickly and sporulates heavily. On agar, it can sometimes be outrun by transferring clean mycelium far away from it.

Cobweb mold

• Looks like: gray-white, very fine and wispy, like spider web. It floats above the surface instead of growing in it, and spreads extremely fast, sometimes across a whole tub in a day or two. Often appears late in colonization or during fruiting.
• Versus mycelium: mycelium is denser and ropier and hugs the substrate.
• Cause: stagnant, humid air and low fresh air exchange.
• What to do: if caught early, spray the patch with 3% hydrogen peroxide. Then improve fresh air in the tub. If it has spread or come back, toss it.

Penicillium

• Looks like: blue-green or gray-green powdery spots, often with a white rim.
• Where: common on agar and grain.
• What to do: toss grain; transfer away from it on agar.

Aspergillus

• Looks like: fuzzy black, yellow-green, or olive patches with a powdery, sometimes granular surface.
• Caution: some Aspergillus species can cause lung infections in people with weakened immune systems. Bag it without opening it, and wear a mask while handling it.

Black pin mold (Rhizopus)

• Looks like: tall gray wisps topped with tiny black dots, like pins in a pincushion.
• What to do: toss.

Neurospora (orange bread mold)

• Looks like: wispy white turning bright orange and powdery.
• Caution: one of the fastest-spreading molds there is. It can colonize in hours and is very hard to get rid of once it's in your workspace. Seal and dispose of it immediately.

Lipstick mold

• Looks like: white patches that turn pinkish-red, usually on the surface of bulk or casing layers.
• What to do: remove it if small, otherwise toss.

Bacteria

• Looks like: wet, slimy, or greasy patches, often gray, tan, or yellowish. In grain jars it shows up as kernels that look shiny, wet, or milky, often at the bottom of the jar, with the mycelium refusing to grow into that area. In liquid culture, the whole liquid turns cloudy.
• Smell: sour, like old socks or rotten fruit. Smell is often the quickest test.
• Cause: almost always too much water. Wet grain, soupy substrate, or standing water in jars. Bacterial endospores also survive short pressure cooks, which is why grain should be soaked first and cooked long enough for your altitude.
• What to do: toss grain and LC. In a bulk tub, a small patch can be scooped out with a sterilized spoon. Fix the moisture problem for next time.

Bacterial blotch

• Looks like: yellow-brown, slightly sunken, slimy spots on the caps or stems of growing mushrooms.
• Cause: water sitting on the mushrooms. Usually from misting fruits directly, or poor air movement.
• What to do: remove affected mushrooms. Mist the tub walls, not the mushrooms, and increase fresh air.

Pests

• Fungus gnats: tiny black flies around tubs. Their larvae tunnel through substrate and mushrooms. Keep filters intact and use sticky traps nearby.
• Mites: tiny moving specks, usually from old substrate or contaminated supplies. Keep work areas clean and keep old grows away from new ones.