Ok, if you are watering overhead, instead of at soil level, that will cause that. High humidity and low wind will do that. Can get that from watering at night.
Ways to stop bud rot
im sure there are more)
Water in the morning. Tests actually show increased yield if you water 1/3 around noon, and another 1/3 every hour or two)
Do not water the canopy, especially at night.
prune up the plant from the ground as it grows, make sure there is plenty of air flow under and through the canopy.
Before you plant, prepare the soil with an organic fungicide and let it dry out.
Make sure you plants are spaced well, to increase air flow.