Pear trellis rust

(Question)

Hello, I have two pear trees which unfortunately have pear trellis rust. I have tried spraying with horticultural oil and liquid lime sulphur in the spring, but to no avail – the orange lesions have returned. I have received advice to try mechanical removal, by pruning all of the effected areas out. This is most of each tree, but I am willing to give it a shot, since I also only have a crop of 2(!) pears. My questions are – is there any risk of long-term damage to the tree if I do a major pruning to remove the pear trellis rust? What is the best means of destroying the cuttings safely, without spreading the fungus? I assume even municipal pickup would be a bad idea. Should I burn them? Dispose of them some other way? (I will also probably be pruning my neighbour’s juniper, as I suspect that is where the rust is spending the winter!) Many thanks for any input.

(Answer)

Pear Trellis Rust is a relatively new fungal disease in Ontario, first recorded in 2007. Unfortunately, can be difficult to treat in urban settings, simply due to population density. It’s caused by the fungus Gymnosporangium sabinae that, as you know, hosts in winter on junipers (although some junipers are resistant). In spring, the orange, gelatinous fruiting bodies (telia) emerge – usually after a rain – and mature to spread wind-borne spores over many kilometers. Some sources suggest the spores can carry for as much as 2-6 km. The spores alight on pear leaves, including those of ornamental pears, and then complete their spring and summer lifecycle – in their turn infecting or reinfecting junipers. And the cycle begins anew.

Advice is often to remove either the pear or the juniper, if they are spaced closer than 150 m (450 feet). In fact, the recommendation is to keep the two alternate hosts at least 1 km apart. You can see why pruning your neighbour’s juniper might not be the solution if other neighbours within a 1-km radius also have infected junipers. However, if you do see galls or telial fruiting bodies on the tree, it would be best practice to prune them out. Depending on the weather, this is best done in March.

The Ontario Ministry of Agriculture and Rural Affairs (OMAFRA) has an excellent fact sheet on Pear Trellis Rust.

 

On the pear trees, it’s the leaves rather than the wood that play a role in the lifecycle of this fungus, so there’s no need to disfigure your trees by pruning. However, do try to gather up and dispose of any fallen pear foliage and fruit; do not add them to your compost. One suggestion is to pluck them off the tree before they fall, but this is impractical for widespread infection.

While there are no fungicides specifically approved for Pear Trellis Rust, OMAFRA suggests that other fungicides might help minimize the impact on your trees. Look for those used to treat other Gymnosporangium rusts, such as cedar-apple rust.

If ever in doubt about a tree problem, it’s always wise to seek out a certified arborist for an on-site consultation. You can find an arborist near you through the International Society of Arboriculture (ISA) website here.

The very best of luck with your pear trees.