WHAT IS IT?
Pear Trellis Rust is caused by the fungal plant pathogen known as Gymnosporengium sabinae. Much like other rust causing fungi, the Pear Trellis Rust fungus requires two hosts to complete it's lifecycle every year. (see cedar-apple rust)
Pear Trellis Rust affects two distinct types of trees. The fungus begins on juniper trees as the primary host, and pear trees as the secondary host. Pear trees are the only species that are a suitable secondary host for the fungus.
HOW TO IDENTIFY:
Identification of Pear Trellis Rust is similar to identifying Cedar-Apple Rust. The branches of an infected juniper will produce horn-like structures covered in a gelatinous orange mass. An infected pear tree will show yellow or orange spots on the leaves and occasionally on the twigs of the tree. Fruiting bodies called aecia form on lower leaf structures. Unlike Cedar-Apple Rust however, the aecia of Pear Trellis Rust develop an acorn-like swelling.
The fungus winters within its juniper host. Come spring, usually after a rainfall, the gelatinous spore-producing horns appear. The fungus is blown from these spores by the wind to their new pear tree host. Once attached to their new host they produce fruiting bodies called aecia. These aecia are also blown by the wind where they will land and infect a new juniper host and the cycle will begin again. The spore producing bodies on both the primary and secondary hosts are capable of producing spores for multiple seasons.
IF LEFT UNTREATED:
Pear Trellis Rust can be particularly damaging to pear crops. If not treated, PTR could result in complete crop loss.
Treatment for Pear Trellis Rust is treated by a fungicide spray similar to the spray used to treat Apple Scab and Cedar-Apple Rust.