Some signs that look like disease are the room talking. ICAR-DMR describes high carbon dioxide at pinning producing onion-shaped mushrooms with a bulbous base and small cap, and later long stalks with small open caps. In oyster the same cause gives a trumpet-mouth shape. No organism is involved; spraying wastes money and adds residue.
Pests are counted, not guessed. ICAR-DMR's sciarid table says any live adult in the first flush is already a reason to act, and from the second flush more than 20 per trap per week. NHB describes the trap: a 15 W yellow bulb over a polythene sheet coated with mustard oil.