My new silverbeet plants seem to have a white mouldy look on the leaves only on the new plants and not all of them, the old ones are fine which we planted the beginning of the year.

Hi Lorraine, it is most likely your silverbeet has picked up some mildew, which is common. To eradicate it, remove the badly affected leaves and treat with a spray which is registered to treat this problem. By removing the leaves you will limit the spread of it to future growth. It is unlikely your older plants will become infested too if you act now, as mildew is more prolific on softer new growth.