At this time of year it is a good idea to thin out any heavy crops of fruit such as Apples, Pears or Plums. This will then encourage the fruit that you do allow to grow to be larger and of better quality. Any new Raspberry canes can be tied in to their supports and any older canes can be cut away from the very bottom at soil level.
Cabbage white butterflies should be kept at bay with some netting over your brassicas. This will prevent them from laying their eggs on your crops.
There was at one time Bordeaux mixture that could be put over potatoes and tomatoes to prevent blight but that has now, like so many other chemical treatments, been taken off the market. There are still other applications that can be used and it is a good idea to do this now.
In the greenhouse remember and keep your plants well watered, in the nice weather things will dry out more quickly and this can spoil your fruits. Keep pinching out side shoots from your tomatoes, you want the goodness of the plant to go into the fruits not foliage that you won’t need.