Health Library

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.

Powdery mildew is one of the most common fungal diseases in cannabis — and one of the sneakiest. It's caused by obligate parasitic fungi that thrive in humid air (above 55% RH) with poor circulation, but here's what trips people up: unlike most fungi, PM doesn't need wet leaves to infect. It actually prefers dry leaf surfaces with moisture in the surrounding air. Spores spread easily through air currents, on clothing, or via contaminated tools, and a single colony can spread through an entire grow room within a couple of weeks if left unchecked. The easiest way to tell PM apart from trichomes is the wipe test — PM rubs off cleanly with a finger, while trichomes are sticky and don't wipe away. If you see white patches that smear when you touch them, you've got powdery mildew. It's especially dangerous during flower because infected buds are unsafe to consume.

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.