Several of my late disbud chrysanthemum flowers are turning brown and rotting, what is causing this? and is there a cure?

The flowers have been affected by a fungal disease known as ‘damping off’.

It is a form botrytis, encouraged by lack of ventilation and damp air.

Enclose the damaged flowers in plastic bags, then cut the blooms off, and dispose of them, this will prevent spreading spores to other flowers during the process.

Ventilate the greenhouse if weather conditions allow, and introduce some heat in dull and cold conditions.

Some of my chrysanthemum cuttings have produced strange growths at soil level.

Is there some fault with the plants or the compost, and is there any cure?

The odd growths are due to crown gall attack.

This is a bacterial infection that may have been in the original plants, rather than in the compost.

Sadly, there is no control.

You could try taking tip cuttings rather than the usual basal cuttings.

There are brown spots on the surface of my spray chrysanthemum leaves and raised buff pustules on the lower surface of the leaves.

Can you tell me what this is,and is there a cure?

It sounds like you might have a disease known as 'White Rust' look in 'Related links' for more information.