Pear Rust is a fungal disease of pears, causing bright orange spots on the leaves. It can also affects junipers. In fact it needs both plants in order to complete its life cycle.
Bright orange spots on the upper leaf surface. As summer progresses brown, gall-like outgrowths develop on the corresponding lower leaf surface. Fruit may be affected, but this is much less common. In mainland Europe the fungus can also cause perennial cankers (lesions in the bark) on the branches, which can be damaging to young trees in particular. So far, however, these have not been common in the UK.
To control, if you have junipers close to your pears, carefully remove rust infections from the stems, or simply remove whole plants will reduce the likelihood of infection (but note that the spores are airborne over quite long distances). This can break the cycle of infection and control the problem.
On your pears if they have the rust remove the worst of the infected leaves and clear any fallen leaves. The best thing to do is to make sure the tree is growing really well and fight any infection. carry out a winter wash, spring feed well and mulch can all help.
Prune out any branch cankers if seen on pear trees.
Unfortunatley there is currently no chemical control that is recommended.
For more info on it check out this link- pear rust at RHS