Answer: When buds turn brown and drop, it is often a sign of either cold exposure, or underwatering. Mandevilla needs soil that is evenly moist (but not sopping wet) during the growing months. If that doesn't seem to be the problem, there may be an infestation of thrips or possibly a fungal infection such as botrytis. There might also be a nutrient imbalance contributing to stress the plant. I would suggest you work with your local county extension to trouble shoot the problem. If it is something that would require a chemical control, they will have the most up to date information on what ot use and how/when to use it.
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