Pear scab is a fungal disease that produces dark, velvety lesions on leaves, fruit, and twigs of pear trees. It’s caused by the fungus Venturia pirina, a close relative of the apple scab pathogen but one that specifically targets pears. Left unmanaged, scab can deform developing fruit, cause premature fruit drop, and lead to cracking that ruins stored harvests.
What Causes Pear Scab
The fungus Venturia pirina overwinters in fallen leaves and infected twig tissue on and around the tree. In spring, it releases spores that travel on wind and rain to newly emerging leaves, blossoms, and fruitlets. Wet conditions are essential for infection: spores need a film of moisture on plant surfaces to germinate and penetrate the outer layer of the leaf or fruit.
Though closely related to the apple scab fungus, V. pirina is pear-specific. Lab studies have shown that when the pear scab fungus lands on apple leaves, the apple tissue mounts a rapid immune response that kills the invading cells. Pear scab isolates are, at most, weak saprophytes on apple. So you don’t need to worry about scab jumping between your pear and apple trees in any meaningful way.
How to Identify Pear Scab
On Fruit
The earliest sign is sooty spots with a soft, velvety texture on young fruit, stems, calyx lobes, or flower petals in spring. These spots expand as the fruit grows, stopping only when dry weather arrives or sprays take effect. Young infected fruit frequently drop from the tree or become visibly misshapen.
On older fruit, scab lesions often crack open. You’ll see a sunken, dark center surrounded by russeted, corky tissue with an olive-colored ring of active fungal growth at the margin. Late-season infections are sneaky: fruit infected roughly two weeks before harvest can look clean at picking, then develop pinpoint-size scab spots a month or more into storage.
On Leaves
Olive-black spots appear on leaves and expand as the leaf grows. Infected leaves often twist or curl abnormally. The spots are frequently more visible on the underside of leaves, where they show up as diffuse dark patches rather than sharply defined circles.
On Twigs
Twig infections appear as small, pinhead-sized blister-like bumps, often concentrated near the base of leaf stems. Many of these lesions develop a corky layer and are naturally sloughed off during summer, but some persist and serve as a source of spores the following spring.
Conditions That Favor Infection
Pear scab thrives in cool, wet springs. The critical window runs from bud break through about a month after petal fall, when tender new growth is most vulnerable and spring rains provide the moisture the fungus needs. Extended rainy periods during this window dramatically increase infection risk, while dry springs can make scab a non-issue in some years. Dense canopies that trap humidity around leaves and fruit create a microclimate the fungus loves, which is why good pruning matters even apart from spray programs.
Fungicide Options and Timing
If your tree has a history of scab or you’re heading into a wet spring, fungicide sprays are the most reliable defense. Several options exist, and most are approved for organic use.
- Fixed copper and Bordeaux mixtures: effective early-season sprays, best used only from green tip (when leaf tips first emerge from buds) through full bloom. Copper can cause fruit russeting if applied later.
- Sulfur (wettable): can be applied through bloom and into early fruit set, giving you a wider window than copper. A good organic option for extended wet stretches.
- Copper soaps and neem oil: additional organic choices with similar early-season timing.
- Myclobutanil: a synthetic fungicide that can be applied any time from green tip through after petal fall. It’s the most flexible option in terms of timing but is not organically acceptable.
The first spray should go on as soon as you see leaf tips emerging from buds, especially if rain is in the forecast. If rain continues, a second application 10 to 14 days later is wise, timed for when you can see blossom clusters but before they’ve opened. A third spray may be needed toward the end of bloom if wet weather persists. The general recommendation is to cover the period from bud break through about a month after petal fall, then reassess based on weather.
Cultural Practices That Reduce Scab
Sanitation is the foundation of any scab management plan. Raking and removing fallen leaves in autumn eliminates a large portion of the overwintering fungus. Pruning out blistered or infected twigs in late winter further reduces the spore load available to start new infections in spring. Disposing of infected fruit, whether dropped or picked, keeps the fungus from cycling back into the soil and leaf litter.
Pruning for an open canopy is equally important. Good airflow through the tree helps leaves and fruit dry quickly after rain, shortening the window the fungus needs to infect. Thinning interior branches so light and air penetrate the center of the tree is one of the simplest things you can do to lower disease pressure across the board.
One honest caveat: sanitation helps most when your tree is relatively isolated. Scab spores can travel long distances on wind, so if neighboring properties have infected, unmanaged pear trees, your own cleanup efforts will be of limited value without some level of fungicide support.
Resistant and Susceptible Varieties
Choosing the right variety is the single most effective long-term strategy against pear scab. A multi-year study of pear cultivar susceptibility found a wide range of responses, from complete immunity to severe infection rates above 80%.
Cultivars identified as immune to V. pirina include Zimovka, Trapezitsa, Chervona, Populyarnaya, and Wonderful Italy, among others. These showed zero disease development across all years tested. Highly resistant varieties like Zhukovka, Zaporozhskaya, Triumph of Jodoin, and Martin Sekl developed scab at very low levels, in the range of 0.2% to 1.3%.
A middle tier of tolerant varieties, including Grand Champion, Luchistaya, and Decanka Boucher, showed moderate infection ranging from about 3% to 17% disease development. These can perform well with minimal spray programs in most climates.
Susceptible cultivars, by contrast, showed disease development between 36% and 83% on average and are poor choices for regions with wet springs unless you’re committed to a rigorous spray schedule. If you’re planting a new pear tree and scab is common in your area, selecting a resistant or immune variety will save you years of management headaches.