Hello Paul,

You can manage pear rust in Michigan by combining timed fungicide sprays with host‑removal practices, and the most reliable guidance comes from university extension programs. The disease is caused by Gymnosporangium rusts (often cedar–hawthorn or cedar–quince rust), which cycle between junipers/cedars and pear trees. Effective control depends on starting at bud break and repeating sprays during the main infection window.

What pear rust does and why timing matters

Pear leaves, flowers, and young fruit can be infected as they emerge, and early infections cause the most severe distortion and spotting. Leaves infected very early show heavy spotting and deformation, whereas later infections produce more scattered lesions. Premature leaf drop and fruit loss can occur. More information at this link:

Pear Rust | Oklahoma State University

Rust spores infect pears in spring, usually during wet periods. A reliable spray‑timing cue is when orange, gelatinous galls appear on nearby junipers, which release spores after spring rains. More information at this link:

Pear Rust.pdf

Cultural steps that help

Check for nearby junipers/cedars (including ornamental junipers). Removing or pruning infected junipers heavily reduces pressure, though spores can travel long distances.

Rake and remove fallen leaves to reduce overwintering inoculum.

Maintain good airflow around the canopy by pruning.

These steps won’t eliminate rust, but reduce the amount of infection you must manage with sprays.

Fungicide options supported by university extensions

While Michigan State University does not publish a pear‑rust‑specific spray schedule, the general fruit‑disease guidance in the Michigan Fruit Management Guide emphasizes choosing fungicides based on disease biology and timing.

From extension recommendations in other states (Kansas State University, Oklahoma State University), the following fungicide groups are commonly used for Gymnosporangium rusts on pome fruit:

Myclobutanil (a systemic DMI fungicide; often sold as Immunox or similar homeowner formulations)

Propiconazole (another DMI fungicide)

Mancozeb (a protectant fungicide; often used early season)

Chlorothalonil (protectant; typically allowed only before bloom on fruit trees)

These are not Michigan‑specific product endorsements, but they are the standard university‑recommended actives for rust diseases on pears and apples.

How to time sprays in Michigan

Use this as a general framework, not a personalized treatment plan:

Bud break (early spring): Begin with a protectant fungicide such as mancozeb or chlorothalonil (if label allows for pears and pre‑bloom use).

Pre‑bloom through petal fall: Switch to or rotate with a systemic DMI fungicide such as myclobutanil or propiconazole. These help protect new growth as leaves expand — the most vulnerable stage.

Repeat every 10–14 days during wet spring weather or when juniper galls are actively sporulating (the orange, jelly‑like stage). Kansas State University specifically notes that sprays should begin when cedar‑apple rust galls on junipers turn orange and gelatinous, which typically follows spring rains. More information at this link:

Pear Rust.pdf

Stop after the main infection window (usually late spring to early summer), once leaves have hardened off and juniper galls dry up.

Always follow the label for your specific product, as labels vary in what is permitted on pears, pre‑harvest intervals, and spray intervals.

Choosing among the options

If you want a simple decision path:

If you prefer a widely available product for homeowners, Myclobutanil is the most commonly recommended for rust diseases on pome fruit by university extension services.

If you want maximum early‑season protection: Start with mancozeb or chlorothalonil (pre‑bloom only), then rotate to a DMI fungicide.

If you have heavy rust pressure (near junipers), use a protectant + a systemic rotation through the main infection window.

One thing that would help refine this

Are there junipers or red cedars within about 300–500 feet of your pear trees? That strongly affects how aggressive your spray schedule needs to be.

I hope this helps!