Pear trees in Ajax, Whitby, and Pickering have looked rough this year. Bright orange-red spots on the leaves, sometimes on the fruit, and by late summer the underside of those spots starts to look like little lanterns or blisters. People call it rust because that's what it looks like.
It is rust. Specifically pear trellis rust, caused by the fungus Gymnosporangium sabinae — you'll still see the old name Gymnosporangium fuscum in older Canadian papers. It has been in southern Ontario since the late 1990s. The CFIA deregulated it in 2013 because it is already widespread here and in B.C. It is not a quarantine panic. It is a two-host problem, and the host that matters in winter is not the pear.
The Part Most People Miss
The fungus does not overwinter on the pear.
When the leaves drop, that year's infection on the pear is over. Next spring's spots do not come from last year's pear leaves the way anthracnose and tar spot do. They come from a round woody gall on a juniper.
That gall can sit on a Savin juniper or another susceptible juniper on your lot, the neighbour's lot, or — and this is the part I keep repeating on jobs — a juniper up to about a thousand feet away. Spores can travel farther than that on a wet spring wind. OMAFRA has recorded dispersal out to several kilometres. The infections that actually wreck a backyard pear are almost always the juniper you can walk to.
If you only treat the pear, you are treating the summer host. The perennial host is the juniper.
What You're Looking At Right Now
By September in Durham, the pear side of the cycle is easy to read if you flip the leaf over.
On the pear
- Upper surface: yellow-orange spots that enlarge and pick up a crimson-red margin. Tiny raised pimples in the centre — those are pycnia.
- Lower surface, late August into fall: brown blisters, then small lantern-shaped cups (aecia). Those cups hold the spores that go looking for a juniper.
- Fruit and young shoots can take lesions too, which is why an ornamental Bradford-type pear and an eating pear both look ugly.
On the juniper
- A spindle-shaped or round woody swelling on a twig or small branch. In winter it is subtle. You will walk past it.
- In mid to late spring, after a warm wet spell, the gall pushes out dark horns that turn into an orange gelatinous mass. That is the spore dump that infects new pear leaves.
- The gel falls off after a few days and leaves a pale scar. The gall shrinks back and waits until next year. These galls are perennial. They sporulate for several years and get bigger.
Juniper usually lives with this. The pear is the one that defoliates, drops fruit, and looks like it is dying when it is mostly just losing this year's leaves early.
Which Junipers Are in the Game
Not every juniper feeds this rust.
Usually susceptible: Savin juniper (Juniperus sabina), plus a lot of the common landscape junipers in J. chinensis, J. scopulorum, and J. virginiana.
Generally resistant, and the ones I will plant near a pear: creeping juniper (J. horizontalis), common juniper (J. communis), and J. squamata.
If you are putting a new evergreen next to a pear this fall, that list is the whole conversation. Right tree, right place includes "do not pair a pear with a Savin."
What Actually Breaks the Cycle
There is no homeowner spray that fixes spots that are already on the leaf. Same rule as the leaf-spot diseases: fungicides are protective, not curative. The infection window was spring, when the juniper was gelling. September is too late for chemistry and exactly the right time to find the other host.
Walk the thousand feet. Start at the pear. Check your own foundation plantings, the hedge on the lot line, the neighbour's rock garden. You are looking for a woody swelling on juniper, not a yellow leaf.
Prune the galls off before April. Cut back into clean wood. Bag the prunings. Do it in late winter or very early spring, before the orange gel appears. In a dense old juniper this is tedious and you will miss some. That is still better than spraying a pear that will just get reinfected from the gall you left.
Remove a sacrificial juniper if the pear is the tree that matters. On a small Ajax lot, one Savin next to a fruiting pear is a yearly rust machine. Taking the juniper out is a one-time fix. Replant with a resistant juniper, or something that is not a juniper.
Rake the pear leaves anyway. They are not the overwintering host for this rust, but they still hold other fungi and they look like hell on the lawn. Off the property, into municipal yard waste — same advice I give for maple leaf spots.
Do not plant the pair on purpose. New pear plus a susceptible juniper on the same lot is how this starts.
Commercial orchards talk about keeping junipers a kilometre or two away. That is orchard math. On a residential street in Durham you cannot enforce a kilometre. You can enforce your own yard and a conversation over the fence.
Why I Usually Will Not Spray This
Under Ontario Regulation 63/09, a conventional fungicide on a landscape tree needs a written opinion from someone with the right credentials — ISA Certified Arborist, registered professional forester, or qualified utility arborist — that the treatment is necessary for the health of that tree. We have to use integrated pest management, and we have to refuse when the treatment is not necessary.
A backyard pear with rust spots and a full canopy is almost never that case. The tree will leaf out next spring. The honest work is finding the juniper.
Orchard pears and a specimen fruit tree that has defoliated early several years running are a different assessment. Protective sprays exist for commercial growers and they are timed to spring juniper sporulation, not to orange spots in September. If someone offers to spray your pear in September for rust, they are selling a treatment whose window already closed.
When It Is Worth a Visit
Come find me if:
- The pear has dropped most of its leaves by September two or three years running — repeated early defoliation drains next year's fruiting wood
- You see cankers or dieback on shoots, not just leaf spots
- You cannot find the juniper and you want a second set of eyes on the lot and the street
- You are about to plant a pear or a juniper and you want the pairing done once
That is tree health care, not a product. A photo of the upper and lower leaf surface is often enough to confirm rust before we roll a truck.
Orange spots on a pear in Ajax, Whitby, Pickering, or anywhere in Durham Region? Send a photo or book a free assessment — I will tell you whether it is trellis rust, and whether the fix is a juniper, not a spray.
