Now you know this, but dont have a system to control it, what will you do?
The rot to which you refer is a root pathogen manifesting in the bud sites to us visibly, but ultimately this is less about the air moisture content "you" have to deal with, and much more about good irrigation and soil temps. We can not dismiss air humidity if we want to grow an "aesthetically human perfect plant", but i suspect you might control your own irrigation and manage soil temps on a low budget, but controlling what God is doing to the air takes dollars and design?
What you can do cheaply...
if you dont have a way to measure soil/ media moisture/ temps, then get something. These tools are cheap and can tell you data which is useful.
Soil/ media moisture/ temps are far more critical than the air around your plant imo.
You
must keep you media temps from peaking for consecutive days, esp around the critical growth markers.
How much DO2 your media can hold is directly related to the temps. The higher the temps the lower the DO2, the lower the DO2 the less respiration can occur, the less mineralisation follows, the less access to minerals fundamental to plant heath, the higher the risk of pathogens and pests.
So keep your media temps under 25C, ideally you want to aim for 18-21C for happy roots.
Moisture - No soil moisture, less microbes in active states. moist is not wet, nor is it damp
Over drying media causes the colonies of microbes to begin to act differently, secreting different compounds in to the soil system to insure their own survival. As ever, the trouble makers are the hardest living bastards, so these can live at the extremes for longer, waiting for the drop in mineral access to open the opportunity for the infection cycle to initiate within our plants. This is evolution and is fundamentally hinged to system balance, esp where things are unstable. Good soil moisture maintains diverse populations of microbes, preventing one type dominating and putting your plant at risk
here is where we join the dots between media temps and DO2 availability, and moisture %. Good DO2, eg above 6ppms plus microbial and plant root respiration, eg (breathing the same as us) its microbes taking in the O2 from the DO2 and breathing out CO2, this combines with H2O to form Carbonic Acid, it is this carbonic acid responsible for mineralisation, eg taking the Zinc or Manganese from the media and offering it to the plant, where it is used to initiate multiple reactions, including up regulating plant health, ergo making it less susceptible to pathogens and or general attack, stress etc..
40%-60% is a good range. having a tool to measure this is a good idea for new growers,, after a while this irrigation stuff becomes almost second nature and you can relax on the tools and rely on your instinct. Otherwise to really own it on day one, you must do the measuring, then the complex maths, and this aint easy in a dynamic system. How much moisture is being used by your plant and its surroundings is based on a great many vectors, calculating this is hard work and a constant job as it is dynamic. However, if you seek a human perfect plant vision, you ought to learn how nature balances energy in dynamic systems, since this will be part of the tool kit needed to make "human measured perfection" repeatable.
Any plant has a short part in its over cycle that is the peak risk zone for late blight. For cannabis you need to aim to have the best conditions leading up to flower, eg 1 week before, and then try to maintain good environmentals up to day 21 of bloom, after which risk substantially drops. Within this wider time frame, there is a much shallower amount of time where the true risk lays, but this is pheno dependent and impossible for anyone to say unless you have dedicated serious time and observation to any strain. This is what is meant by knowing your strains. Just because you are seeing it in week 7 dont mean it occurred then
