Nematodes are tiny, very primitive round worms. They thrive in raw compost and can exist in excessive numbers during the mushroom growing process. To learn more, please see the Pennsylvania Mushroom Integrated Pest Management Handbook, pages 78-84.

Nematodes associated with cultivated mushrooms can be divided into two groups: saprophagous, that feed on bacteria and finely divided organic matter in the compost and mycophagous, that feed directly on the mushroom mycelium. Nematodes or eelworms find mushroom beds a favorable place to live. Nematodes are up to 1 mm in length and when swarming they can rope together, forming glistening white masses that wave and glisten in torchlight. They need free water to survive, but can survive dry conditions for some time. Their main source of entry is through infested casing or surviving poor Phase II composting.

Saprophagous nematodes are by far the most common type of nematode found on North American mushroom farms. They occur in low numbers in poultry manure and dry straw, but in much higher numbers in wet straw. Live nematodes can be found in the cooler, outer zone of Phase I stacks. Nematodes also regularly occur in peat moss, some sources containing more than others. Although saprophytic nematodes feed on bacteria, they can tell the difference between various bacteria and prefer to feed on those not compatible with a selective compost. This is a Phase II, conditioning problem, not a kill phase problem (Ross and Burden 1981). Hence, although saprophytic nematodes will build up in numbers in a selective compost, they will build up to much higher numbers in a less well prepared compost. This is a Phase II, conditioning problem, not a kill phase problem and bacteria feeding mites can occur together with nematodes. Saprophytic nematodes are sometimes associated with deformed mushrooms and bacterial blotch lesions. Poor quality mushrooms often have increased populations of bacteria plus saprophytic nematodes (Grewel and Richardson 1991; Allan 2001). Saprophytic nematodes can be associated with severe yield losses. Off-white hybrids are more susceptible to yield reductions and quality problems than white hybrids.

Mycophagous nematodes are rarely found on North American farms. Following infestation, the compost becomes waterlogged and has a foul odor.