Certified GKH Gardening Expert
Plants generally drop their flower buds when they are stressed in some way. Anything from insect pests, disease, and environmental changes can lead to bud drop. If, for instance, the temps have recently changed in a drastic way, such as a sudden heat wave, then your plant would respond by dropping its buds. Watering can also be a factor. I don't believe the slugs are affecting the plant; otherwise, you would be seeing holes in the foliage as well.