General rule is the larger/more dense your buds are, the higher your risk for mold: the lower you want your humidity. Smaller nugs aren't nearly as susceptible as mold. For example, colas that are lets say somewhere on the scale between Bic lighter to highlighter sized, perhaps a tad larger, are not so susceptible to mold. At least, not with fairly vigorous plants blooming where the humidity doesn't exceed 65%.
When buds are much larger than a typical yellow highlighting marker, or wider than the rim of a shot glass, or approaching paper-towel tube/core or, especially, water bottle sized proportions... then it becomes a real concern, even at 40% RH.
Many strains naturally have a sweet, slightly sour smell to the fresh buds. Bud rot would make them smell more rancid and musky. It would typically start in the main cola, at the deepest and densest spot, or the mid-section where the other colas branch off (but tend to clump together when mature).
You often can't even tell that a plant/cola has become infected with botrytis on the inside just by casually looking the colas over: until it is too late. Otherwise the buds tend to look just fine on the outside (mostly). But, if you were to open them up, or pull some of the clustered colas aside, you might see the white-gray fuzz in there.
Prior to this point, there are a couple other signs to watch out for: one is yellowing/crispy leaves- particularly the secondary leaves (not the large fan leaves, the smaller leaves). If you see that secondary leaves growing out from the mid-section, or upper parts of the cola, have unnaturally shriveled up (while fan and other lower leaves look okay) that can be an indication of botrytis.
The 'petiole' is the little stem that attaches a leaf to a branch, or the rest of the plant. If you have shriveled leaves like I just described, pluck them off and examine the base of the leaf's petiole. You may need tweezers to help pluck a petiole clean away from a cola/the inside of a bud. If there is a problem like mold, chances are you'll see it on the petiole. You may see fuzz on the base of the petiole, or notice it is brown, mushy, discolored (white) or just doesn't seem right.
Another sign is discoloration on the inside of the bud, or at the central cluster of colas. I notice this more on larger/denser colas and I consider it to be indicator that mold is on the way. The base of the inside of the cola tends to be more yellow-green or even white in some places. Pretty sure this is caused by the lack of light and restricted air flow in the deep recesses of larger buds: which leads to mold.
I think humidity and air flow are much more significant factors for botrytis than temperature. Molds can grow in both cool and warm weather. My feeling would be that most molds probably grow faster with warmer temperatures anyways. What you'd really want to do, other than keeping RH below 45%, is make sure you also have constant airflow/ventilation. Make sure you have an oscillating fan on, especially during dark hours, and/or keep your exhaust on low during dark hours.
This is especially important if you have a tent, or a sealed room. There should be constant airflow. Also make sure you refrain from spraying anything at all on the plants as they are finishing, and only water them when necessary shortly before or after lights on.
