Health Library

Fungus gnats are tiny dark flies that hover around your soil — annoying, yes, but the adults themselves aren't the real problem. It's their larvae you need to worry about. These translucent white maggots live in the top few inches of wet soil and feed directly on roots and root hairs, creating wounds that let dangerous pathogens like Pythium and Fusarium invade. The larvae are the ones that transmit Pythium — they ingest fungal oospores in the soil and spread them through their excretions. Adults do carry other pathogens (Fusarium, Botrytis, Verticillium) on their bodies as they fly between plants, but they don't vector Pythium themselves. Overwatering is the root cause — wet soil grows the fungi and decaying organic matter that attract egg-laying females in the first place. Fix the moisture problem and you cut off the cycle. Don't confuse these with whiteflies — gnats are dark and hover near the soil, while whiteflies are white and cluster on leaf undersides.

Mealybugs are soft-bodied scale insects coated in a white waxy armor that makes them look like tiny cotton tufts. They cluster at stem joints, leaf axils, and under leaves — anywhere they can quietly tap into sap flow. Like aphids, they excrete honeydew, which attracts ants and invites sooty mold. Their waxy coating repels many sprays on contact, so repeat treatments are essential. If you touch what looks like mold and it moves, you've got mealybugs — that's the quickest way to tell them apart from powdery mildew or other white residues.

Bud rot (Botrytis cinerea) is one of the most destructive diseases you'll encounter during flowering. The critical thing to understand is that it starts from the inside of the bud and works outward — by the time you spot external signs, the interior is already compromised. It thrives in dense, tightly packed colas where humidity gets trapped, especially when airflow is poor and RH stays above 60%. Caterpillar damage is a major entry point — the wounds and frass they leave behind create perfect conditions for Botrytis spores to germinate, so if you're finding caterpillars, inspect those buds first. Unlike powdery mildew which sits on leaf surfaces and can sometimes be treated in place, bud rot penetrates deep into tissue and any infected material must be completely removed. Infected buds are unsafe to consume due to fungal toxins (botrydial, botcinic acid) and spore contamination — this applies to buds that were directly adjacent to infected ones too, since they likely harbor spores even if they look clean.

Root rot is caused by pathogens — primarily Pythium and Fusarium — that thrive in waterlogged, oxygen-depleted root zones. It's the end result of chronic overwatering, poor drainage, or root zone temperatures above 72F/22C. The key distinction from simple overwatering: overwatered roots are still white and firm (just sitting in too much water), while root rot roots are brown, slimy, and smell terrible. Fungus gnat larvae make things worse — they chew on roots and create entry points for Pythium, so if you're seeing gnats, check for rot too. Seedlings and freshly transplanted plants are especially vulnerable in the first three weeks — they can collapse at the soil line overnight (damping off). In hydro systems, root rot spreads through the reservoir fast and can take out an entire grow. Early intervention is critical because once the root mass is mostly brown and mushy, the plant rarely recovers.