Jonno writes:
I am concerned that after using a tomato dusting powder, that the bees have
gone missing in my garden.

As you acknowledge, it is far better to be concerned about collateral
damage BEFORE spreading an insecticide. :-(

While I would like to prevent tomato diseases which have decimated my tomato
plants later on in the season, with the leaves curling up, and going brown
and drying up. I am not sure of what do.

Everyone's tomatoes die like this, eventually, in Australia. Tomatoes are
pre-destined to die of disease, one way or another, it seems. Their
mediterranean home doesn't have the high summer humidity that they find
in Australia.

what else can you do to prevent diseases?

You already know the answer: don't wet the leaves when you water!

Pick off lower leaves, the ones most likely to pick up fungal spores from
the soil. Grow on stakes, and thin foliage if it looks like bunching, so
air circulates better.

There is opportunity to experiment with companion planting (basil).

But my primary suggestion for the home gardener: grow cherry tomatoes,
and get them in early in the season. Their fruit sets and ripens so
quickly that many diseases don't get a foothold, and they seem to be
overlooked by both fruitfly and, I've found, thieving birds.

Besides, each cherry tomato is a small morsel, so pop it into your
mouth and eat it whole, no need to inspect for fly larvae! What the
eye doesn't see, the mind doesn't worry about.
--
John Savage (my news address is not valid for email)