Agar contamination identification guide — what are these colors telling you?

Green = Trichoderma (almost certainly). Hard abort on that plate. It spreads aggressively and will wipe out your entire agar game if you let it. Black is usually Aspergillus. Pink/red can be Neurospora (the worst — it spreads by air). Bacterial contamination shows as wet, slimy growth, often with a smell.

Important clarification: bright white, cottony growth that comes in from a specific point is almost certainly mycelium from a contaminated inoculation point, not contamination itself. The key distinction: does it have the right mycelium texture? Does it smell clean?

Sectoring on agar (wedge-shaped faster-growing zones) is not contamination — it's genetic variation in your culture. Those faster-growing sectors are candidates for isolation. Contamination looks foreign; sectoring looks like the same organism running faster in one direction.