Pear Tree Rust Disease - a Fungus growth - can affect both Pear tree leaves and also those of the Juniper family.
It is easily identified, though has to be 'looked for' during the initial stages of infection, and is normally visible in late July - but then decidedly more active in the months from August through late September.
The normal leaf spotting that occurs with the onset of leaf drop in the autumn should not be confused with Pear Leaf Rust Disease.
The first sign of Pear Tree Rust will be the small but very visible bright orange leaf spots - later enlarging - on the surface of the Pear Tree leaf. A closer inspection will reveal typical rust fungal growths on the underside of the leaves. These rust fungus leaf spots house the spores which are easily spread in the wind.
The Pear Rust infection will not kill your pear tree, for it only lives on live tissue, and a dead tree serves no useful purpose to the clever Rust Fungus. It will however weaken the tree for the current and following year.
After having its feed upon your particular Pear Tree, the Pear Tree Rust Fungus will move on via spore transportation - but this time to a Juniper Tree or shrub. This is where it will spend a further year, and then find another Pear tree for the following year. This clever swapping of food supplies ensures a continuous supply of food material for the rust. Not stupid!
The Pear Rust is visible on Juniper bushes by way of large orange clusters of needles - almost deformed - rather than by the small spots which are the hallmark of the beginning of Pear Rust on the Pear Tree hosts. In the case of Juniper infection, it will be necessary to remove complete branches to get at the diseased areas.
Physical Control of Pear Tree Rust Fungus. The affected leaves should be removed as soon as found. This should be done as carefully as possible, bearing in mind that the released rust spores are easily spread in the wind - over large distances. The earlier you can do this will lessen this possibility. All removed material should be burnt, and not put on a compost heap.
Together with this, the normal removal of diseased and dead wood by pruning will help. It is suggested that all Pear Canker growths are pruned out as well.
Chemical Control of Pear Rust Fungus. There seems to be no chemical that has been developed (available to the amateur gardener) that is specifically for the treatment of Pear Rust. However, there are several chemical options - notably those chemicals that are specifically for Pear Scab - that will effectively control the Rust disease. 'Bayer Garden Systhane Fungus Fighter' is one such chemical and freely available as is 'Westland Plant Rescue Fungus'.
It has been noted that where commercial growers of Pear Trees regularly spray for Pear Scab, there is no incidence of Pear Tree Rust Disease.