No. Apple scab and cedar-apple rust are two different fungal diseases that can both affect apple trees, but they come from different fungi, spread in different ways, and produce visibly different symptoms on leaves and fruit.

What Causes Apple Scab Versus Cedar-Apple Rust?

Apple scab is caused by a single fungus, Venturia inaequalis, and it only needs an apple tree to complete its life cycle. It's most aggressive when spring weather stays mild, between 60 and 70 degrees Fahrenheit, with wet conditions.

Cedar-apple rust works differently. It can't survive on apple trees alone and instead alternates each year between an apple tree and a cedar or juniper tree, using both hosts to keep reproducing.

How Do the Leaf Symptoms Differ?

Apple scab starts as small brown spots on the undersides of leaves, then spreads to the top surface as the infection progresses.

Cedar-apple rust looks noticeably different. It begins as small pale yellow spots on the upper leaf surface, which grow larger over the season and develop small black or brown spots in the center, giving the lesion a distinct two-tone appearance.

How Do the Fruit Symptoms Differ?

Apple scab produces light brown spots on fruit, about a quarter to a half inch across, with a texture that feels rough to the touch. Infected fruit often becomes misshapen or cracked and may drop before it ripens.

Cedar-apple rust also causes premature fruit drop as the infection advances, though its fruit-specific appearance isn't as clearly documented as its leaf symptoms.

Does Treatment Differ Between the Two Diseases?

Apple scab responds to Liquid Copper Fungicide Spray, sprayed to the point of runoff on leaves and fruit during the wet spring window.

Cedar-apple rust calls for a different product. Spraying Fungi Max Multi-Purpose Fungicide onto new growth as soon as it emerges in spring protects the apple tree during the period when spores are arriving from a nearby cedar or juniper.

Can a Tree Have Both Diseases at the Same Time?

Yes. Since apple scab only needs an apple tree while cedar-apple rust needs a second host nearby, an apple tree nowhere near a juniper can still develop scab, while one planted close to a cedar could show both problems in the same wet spring. The yellow, dark-centered spots of rust and the brown, rough-textured spots of scab are distinct enough to tell apart on the same leaf.

Frequently Asked Questions

Can removing a nearby juniper prevent apple scab too?

No. Apple scab doesn't need a second host to spread, so removing a juniper only reduces cedar-apple rust risk, not apple scab risk.

Where does each fungus spend the winter?

Apple scab overwinters in fallen leaf litter beneath the same apple tree, while cedar-apple rust overwinters in galls on a separate juniper or cedar host.

Can a single fungicide treat both diseases?

Not necessarily. Liquid Copper Fungicide Spray is labeled for apple scab, while Fungi Max Multi-Purpose Fungicide is labeled for rust, so treating both often means using two different products rather than one that covers both by name.

Does having both diseases mean the tree needs to be removed?

No. Both are manageable with the right fungicide timed to the growing season, combined with sanitation steps like raking fallen leaves, rather than requiring tree removal.