Quince are affected by several types of rust that are caused by various Gymnosporangium species. The key to management is to remove one of the two hosts that it needs to complete its lifecycle. Typically, the primary host is either a juniper or cedar tree, and the secondary host, a rosaceous tree or shrub (or in your case, a quince tree). In the spring, the spores travel from the primary host to the rosaceous host, and then in late summer/early fall, from the rosaceous host back to the juniper or cedar. If you can track down the primary host, likely a juniper or cedar tree that is growing in your yard or neighborhood, and remove it, then this can significantly reduce the severity of the disease. Fungicides are not very effective, largely due to the distance in which the spores can travel to cause new infections in the host plants, but the key is to time the spray so that any new growth (buds and leaves) that emerge in early spring are protected. Typically, this means spraying between mid-March and mid-May. For home gardeners there aren’t as many options, but Bonide Fung-onil is available locally in most garden centers and will provide some protection. If you can prune out visible galls or swelling on the juniper or cedar in early spring, then that will remove the host of infection before they sporulate. Also, prune your quince tree to open it up and improve air flow and allow for more sunlight into the canopy.

To answer your question about the lifespan of the tree, the symptoms are largely cosmetic, and may not affect the life span of the tree. The tree will likely produce fewer fruit or produce fruit that is misshapen and infected with orange rust spores. If you are unable to remove the host, then the tree will continue to be infected and may slowly decline over time. For more, refer to the PNW handbook information on quince rust and hawthorn rusts.