Question
i have some healthy roses... or they were, I noticied this morning loads of rose buds - unopened have just fell off the plant... approx 100 and i dont understand why..

Answer
There can be a few reason why your rose buds have  fallen off. Beetles can bite rose buds off. Small animals can bite them off but they usually eat some of the buds. Insects can lay their eggs in the base of the buds and when the worms hatch they kills the rose buds. If you see a pin hole in the base of the  buds then this is the problem. If there are tiny worms in the buds then this is what caused it. If the weather suddenly  turned hot , roses will drop their buds. And the last reason can't be explained because for some unknown reason roses, as well as some other plants, will drop a lot of buds. You see it more often in fruit tree when they let go of the small fruit because the tree can't support them, is called the June drop.