The short answer
Early bud rot shows up as one sugar leaf turning brown or gray while the leaves next to it stay green. Pull that leaf gently. If it comes away with almost no resistance and the stem end is soft or tan instead of green and firm, you are looking at rot, not normal fade. Smell the spot next. Rot smells like wet hay, a damp basement, or ammonia. Open a dense bud over white paper and watch for a faint puff of gray dust. That dust is spores.
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Why botrytis is hard to catch
Botrytis cinerea starts on the inside of a cola, where air barely moves. The outer surface can stay dry and look fine for days while the core stays humid. By the time gray fuzz appears on the outside, the fungus has usually worked down the stem. That is why the earliest reliable signs are a single dying leaf and a change in smell, not visible mold.
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Signs in the order they tend to appear
- One sugar leaf browns from the stem outward while its neighbors stay green.
- The leaf pulls free with little or no tug.
- A tan or gray patch appears where the leaf met the bud.
- The stem inside the bud feels spongy, or it crumbles instead of snapping clean.
- The flower smells like hay, ammonia, or sour cardboard instead of its usual terpenes.
- Gray or white fuzz shows at the base of a calyx cluster.
- Brown spreads across the bud and into neighboring buds.
What it is not
Late flower fade is even and gradual. Leaves turn yellow, purple, or rust from the top down, and the stems stay firm. Light burn leaves crisp tips near the canopy. Spider mites leave fine webbing and speckled leaves. Powdery mildew sits on the surface as white powder you can wipe. Bud rot is patchy, it starts inside, and the tissue underneath goes soft and brown. If the stem is mushy, treat it as rot no matter what the outside looks like.
Conditions that set it up
- Relative humidity above 55 to 60 percent late in flower.
- Cool nights with warm days, which pushes moisture into the buds.
- Still air or a canopy too dense for airflow.
- Overwatering, or watering late in the day.
- Caterpillars and other chewers that open wounds on the bud.
- Too much nitrogen late in flower, which keeps tissue soft.
Checking flower you bought
Most legal states require microbial testing, but a lab result covers a sample, not every gram in the jar. I still check. Break one bud apart over white paper, look at the stem, and give it a full minute before you judge the smell, since jar aroma can hide a lot. Squeeze a bud: it should feel springy, not damp or spongy. Look for dark patches at the calyx base and any gray strands. A clean batch smells like the strain, not like the storage room.
If you find it
Do not smoke, vape, or cook with moldy flower. Heat does not remove the risk; the spores and any fungal byproducts are still there. Inhaling mold spores can irritate airways and trigger coughing, wheezing, and sinus problems, which matters more if you have asthma or a weakened immune system. Bag the flower, keep the label with the batch or lot number, and take it back to the dispensary or contact your state cannabis regulator. Retailers usually want that batch number so they can pull the rest.
Growers should cut the affected branch an inch into clean tissue with sterilized shears, bag it without shaking it, and get it out of the room. Do not compost it near your plants.
Prevention, short version
- Hold late flower humidity near 45 to 50 percent.
- Keep air moving with fans that stir the room instead of blasting one cola.
- Defoliate enough that light and air reach the lower sites.
- Never water the buds, and water early in the day.
- Scout daily once colas get dense. Two minutes a day beats losing a plant.
Bottom line
The earliest tells are boring: one brown sugar leaf, a stem that gives instead of snaps, and a smell that drifted from skunky to damp. Check those three things daily and you will catch most rot while it is still one branch. Wait for visible fuzz and you are already cleaning up.