We have and apple and pear tree in the garden but don't know a huge amount about them and get fruit more by luck than judgement. The apple tree occasionally produces two varieties of apples but we are guaranteed a good crop from at least one variety on one side. The pear is a real disappointment, almost every year we get really bad rust which I am led to believe comes from a juniper that we cannot find. I am thinking of cutting it back really harshly and seeing if we can break the cycle. Anyone with any ideas?
Pears can be funny things. They don't do well out here in the fens, and I might only get useable fruit one year in every five. The rest of the time, I supply the military with ammunition.
Some apples are biennial bearers, but it sounds like one of the varieties on your dual tree doesn't have the right pollinator.
This is something gardening catalogues don't tend to mention when it comes to dual variety trees. For instance, I have a dual variety tree with golden delicious and jonagored. I'm lucky, I do get apples on both sides of the tree, but that's because I have other varieties, i.e. james grieve, egremont russet, bramley, plus crab apples, in the garden, as jonagored cannot be pollinated by its parent varieties - of which golden delicious is one.