pear brown spot

Symptoms

Round 2-5mm reddish-brown leaf spots on upper foliage, dark depressed lesions on developing fruit around stem-end + lenticels, fruit rot + dropping pre-harvest.

Plants affected

• European pear
• onion
• quince

Easily confused with

• onion downy mildew

  How to tell them apart: Stemphylium vesicarium (Stemphylium leaf blight) starts as small whitish-to-yellow spots, usually on the side of the leaf facing the wind or after hail/insect injury, that elongate into tan-to-brown spindle-shaped necrotic lesions; in humid weather these turn olive-brown to black and velvety as the fungus sporulates densely, and the leaf tip dies back. Peronospora destructor (onion downy mildew) produces longer, paler, diffuse yellow-green oval patches with indistinct margins, and its diagnostic sign is a fuzzy grey-to-violet/purplish downy growth on the lesion surface, most visible in early morning dew or fog; whole leaves bend, yellow and collapse from the tip. Key tell: a velvety BLACK fuzz means Stemphylium, while a GREY-VIOLET fuzz means downy mildew. Because Stemphylium often invades old downy-mildew lesions, look at the freshest leading edge of a lesion, not the dead centre, to identify the primary pathogen.

• onion leaf blight

  How to tell them apart: Botrytis squamosa (Botrytis leaf blight / 'blast') shows tiny (1-5 mm) whitish to silvery, oval-to-elongated leaf spots, each usually surrounded by a pale water-soaked or light-green halo, scattered over the leaf; in humid weather many spots coalesce, the leaf tips dieback and the whole leaf scorches, but you rarely see dark mould unless tissue is dead. Stemphylium vesicarium (Stemphylium leaf blight) instead produces lesions that quickly turn yellow then tan-to-brown, elongating along the leaf, and most distinctively develops a dark olive-brown to almost black velvety sporulation over the centre of older lesions. A key field tell: Stemphylium preferentially colonises tissue already weakened or dead (it often takes over Botrytis blast spots, tip dieback or ozone injury), so dark sporulating patches sitting on top of pale silvery flecks usually means Stemphylium has followed Botrytis. Botrytis spots stay pale with a halo and lack the dark fuzzy centre.

• onion thrips

  How to tell them apart: Stemphylium vesicarium (Stemphylium leaf blight) starts as small pale-yellow to tan, water-soaked oval spots on onion leaf blades, often beginning at the leaf tip or on the side facing the prevailing wind. These spots enlarge into the diagnostic elongated diamond (lens) shape, turn light brown then dark olive-brown as the fungus sporulates, and the leaf tip dies back and collapses. Look for a velvety dark fuzz of spores in the lesion centre under humidity, and lesions that stay in place rather than following insect movement. Thrips tabaci (onion thrips) instead produces silvery-white to whitish patches of stippling concentrated in the protected leaf axils and on the inner youngest leaves, with no defined diamond shape. The silvering is a film of empty, air-filled feeding cells, and you will find tiny (1-1.5 mm) slender yellow-brown insects and dark varnish-like fecal specks among the scars, which a fungal lesion never has.

• pear scab

  How to tell them apart: Stemphylium vesicarium (pear brown spot) makes small, rounded reddish-brown to chocolate-brown leaf spots, often with a paler centre and a diffuse yellow halo; on fruit it gives flat-to-slightly-sunken dark brown lesions with no fuzz, and it spreads fastest in warm humid summer weather and from leaf litter. Venturia pirina (pear scab) produces lesions that start olive-green and look smudgy or velvety because of dark sooty spore growth on the surface, with diffuse feathery margins; on fruit the spots turn black, become rough, corky and crack as the fruit grows. The decisive sign is the velvety olive-brown sporulation coating and corky cracking of scab versus the dry, clean, reddish-brown spots of brown spot.

• entomosporium leaf spot

  How to tell them apart: On quince and pear leaves, Diplocarpon mespili (Entomosporium leaf spot) produces many small, circular reddish to reddish-brown spots, each typically with a slightly darker or grey-purple centre. The diagnostic clue is a tiny dark, raised fruiting body (acervulus) in the centre of mature spots — with a hand lens it looks like a minute black dot or insect-shaped speck. Spots stay roughly round, scatter densely across the whole leaf blade, and merge under heavy infection, triggering yellowing and early leaf drop. The disease favours cool, wet spring conditions and splashing rain on young foliage. Stemphylium vesicarium (brown spot) on quince and pear starts as small reddish-brown to dark necrotic flecks that enlarge into irregular brown lesions, often with a paler tan centre and a diffuse reddish or purplish halo around the margin. Unlike Entomosporium, it lacks the discrete central black fruiting body; the necrosis looks more diffuse and water-soaked, and lesions are often concentrated near leaf margins and tips. On fruit it forms dark, sunken circular rot. It is driven by warm, humid summer weather and is associated with dead plant debris (e.g. nearby senescing leaves or weeds) acting as inoculum.

Common questions

How do I recognise pear brown spot on European pear?

Round 2-5mm reddish-brown leaf spots on upper foliage, dark depressed lesions on developing fruit around stem-end + lenticels, fruit rot + dropping pre-harvest.

Do I have to report pear brown spot?

No. pear brown spot is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is pear brown spot treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.