If the rose is being held in hand, one can purchase a
"Wilting Flower" at pretty much any magic shop. This
is purely a mechanical trick which requires little or no
practise, but whose construction is difficult to
explain.

If the rose is in a vase or on a table, then it will
require some minor mechanics and a person to
operate them as follows:

First: construct your fake rose on a LONG piece of
very thin or flimsy wire. The idea being, the weight of
the rose will cause the wire to bend.
Second: Insert the wire into a soda straw (or cylinder
of similar dimension) which has been painted green
or decorated to look like a stem. Two or more may
need to be attached end-to-end to get the right
length.
Third: Insert this contraption into a vase with a hole
in its bottom. This will need to be operated by
someone either under the table or standing very
close to it.

EFFECT:   With the straw holding the rose aloft (and
secured in this position by a simple piece of tape at
the bottom), all you need to do is cue the person
operating the prop. They simply hold the wire steady
with one hand, while slowly lowering the straw with
other. The weight of the flower will cause the rose to
tilt, giving the appearance it is dying.

For added effect, place a few loose "rose petals"
inside the fake rose. As the bloom tilts forward, the
loose petals will fall out, giving further drama to the
illusion. Cheers!

We also used three different roses, but for the final petal fall, we used a magnet, embedded in the petal. When we switched off the power to the magnet, the petal fell. Very easy.