Apple scab, and mildew alongside it

Apple scab is caused by Venturia inaequalis. The fungus overwinters in fallen leaves on the orchard floor, where it completes its sexual stage and produces fruiting bodies that release ascospores in spring. Release is triggered by rain, and it begins as soon as there is green tissue for the spores to infect — which is to say from bud burst onwards.

Infection requires a period of continuous leaf wetness, and the length required depends on temperature: warmer conditions need less wetness, cooler conditions more. This relationship is the basis of the infection-period models growers use to decide whether a wet spell warranted a fungicide. In a maritime spring those conditions are met repeatedly, which is why scab is a permanent condition of cider country rather than an occasional visitor.

Once primary infections have established on leaves, the fungus switches to an asexual cycle producing conidia, which are splashed onto new growth and cause secondary infections through the summer. This is what turns a modest early infection into a defoliating one by August, and it is why early-season control matters disproportionately.

The visible damage on fruit — corky, olive-brown lesions that crack as the fruit grows — is cosmetic from the press’s point of view. It is worth being explicit about this, because it is the clearest single instance of cider fruit being a genuinely different crop: the standard that governs dessert growing simply does not apply.

The real costs are on the leaves. A tree that loses a substantial part of its canopy to scab fixes less carbon, which shows up as smaller fruit, lower sugar, poorer flower initiation for the following year and reduced winter hardiness. That is a yield and gravity penalty, and it is invisible if only the fruit is inspected.

The second real cost is that scab cracks fruit, and cracks are entry wounds. A scabbed, cracked apple lying in wet grass is colonised far faster than a sound one, so a heavy scab year tends also to be a heavy rot year. The disease that does not matter cosmetically therefore matters indirectly, through the disease that does.

The most important measures are cultural and happen outside the growing season. Because the inoculum overwinters in leaf litter, anything that removes or decomposes that litter reduces next spring’s spore load: mowing and mulching leaves so they break down faster, applying urea to accelerate decomposition, and in intensive systems collecting leaves outright. In a grazed orchard, stock and earthworms do a good deal of this work.

Canopy management is the second lever. An open canopy dries faster after rain, and drying faster is the direct control on infection period length. Pruning for light and air is therefore a disease intervention as much as a yield one, which is worth remembering in orchards where pruning has lapsed.

Fungicide programmes are standard in commercial bush orchards and largely absent from traditional standard orchards. This is not principally a philosophical difference: spraying a hectare of forty six-metre trees is impractical and uneconomic, whereas spraying a hectare of a thousand three-metre trees is routine. The traditional orchard is low-input partly by design and substantially by geometry.

Powdery mildew of apple, caused by Podosphaera leucotricha, overwinters inside dormant buds rather than in leaf litter. Infected buds break in spring to produce silvered, distorted shoots covered in white spores — primary mildew — and those spores infect the surrounding new growth through the summer.

Because it does not require free water, mildew spreads under warm, humid but rainless conditions and is often worst in the seasons that suppress scab. A grower in a maritime cider region will generally be more troubled by scab, but a dry spring can invert that in a single season.

Control begins with pruning out the silvered primary shoots in spring, which removes the inoculum at source and is the one intervention available in an unsprayed orchard. Mildew is generally a lesser problem for cider than scab and canker, and it earns attention mainly where a susceptible cultivar is grown in a drier district.