Pear Rust, Gymnosporangium sabinae (aka Pear Juniper Rust or Pear Leaf Gall)

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We have had a dwarf patio Pear Tree (Pyrus communis) in our garden for several years. It is not a great cropper, with only a couple of fruit each year, though it is very beautiful in spring, when it is covered with a mass of flowers (see photograph below).

This year it has provided some extra interest, with bright orange patches on the uppersides of several of the leaves, suggesting some kind of rust fungus. However, the disease wasn’t listed in my guide to plant pests and diseases (“Pests, Diseases and Disorders Of Garden Plants” by Stefan Buczacki and Keith Harris, Harper Collins 2000).

As summer continued, brown, gall-like outgrowths developed on the lower leaf surfaces below the orange patches. I was now less sure that I’d found a fungus. I took some photographs:

Pear Rust, early October (leaf upperside)

Pear Rust, early October (leaf upperside)

Pear Rust, early October (leaf lowerside)

Pear Rust, early October (leaf lowerside)

When I took a look on the internet and searched for “pear leaf gall” I found a piece by Harry Green on the Worcestershire Biological Records Centre website, describing a gall on Pear tree leaves (Worcestershire Record No. 21 April 2007 p. 49). The article was very helpful and included photographs of the gall on Pear, caused by the fungus Gymnosporangium sabinae.

Searching for Gymnosporangium sabinae has yielded more information on the RHS website. G. sabinae is also known as the Pear Juniper Rust because its other host is Juniper. The fungus overwinters on Juniper, where it forms a perennial infection on the stem. In spring these produce orange, horn-like outgrowths, which produce wind-blown spores. The spores then reinfect Pear trees.

The Worcestershire Record article includes a photograph of the fungus on Juniperus sabina. Wikipedia also has some good pictures on both hosts. (I have since found that my plant pests and diseases book has an entry for the related Hawthorn Rust, G. clavariiforme.)

The iSpot website also has some good photographs of the fungus. iSpot is provided by The Open University as part of the OPAL project and is an excellent way of sharing and identifying natural history observations.

Gymnosporangium sabinae is on the increase in Britain. I visited Holkham Walled Garden at the end of September and found that most of the Pear trees had the galls on their leaves. As for my Pear tree, I removed and destroyed the infected leaves to contain the infection, though I’m sure it’ll be back if there are Juniper bushes in the neighbourhood.

Pear blossom

Pear blossom

Update April 2017: Since we moved house, our patio Pear tree has been in a much sunnier spot and now yields around fifty fruit in most years. The rust reappears every year, but we remove infected leaves as soon as we find them and the tree remains in good health.

In Praise Of Persicaria

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Polygonum affine in autumn colours.

Persicaria affinis in autumn colours.

Two of my favourite herbaceous plants of late summer and early autumn are both in the genus Persicaria: Persicaria affinis and Persicaria amplexicaule. In English these plants are bistorts or knotgrasses, members of the Dock Family, Polygonaceae.

Persicaria affinis is a semi-evergreen perennial that spreads to form a wide mat. The leaves are dark green and elliptical and erect spikes of small white, pink or red flowers are borne above these from July to October, reaching between 20 and 30 cm high. In autumn the leaves turn red or pink. Provided the soil isn’t too dry Persicaria affinis can be grown on a sunny bank and will trail over the edge.

Good varieties of Persicaria affinis include ‘Superba’ (rose pink flowers), ‘Donald Lowndes’ (pink flowers) and ‘Darjeeling Red’ (red-pink flowers). We have the latter two in the garden at The Belvedere Centre and ‘Darjeeling Red’ at Grapes Hill Community Garden, where it is making an escape bid beyond the garden railings and softening the edge of the adjacent car park.

Persicaria amplexicaule is a much more robust plant, growing to 1.2 metres tall with large, prominently veined ovate leaves and small flowers borne in dense, long-stalked spikes which are up to 10cm long. It looks more like a dock than P. affine. It is happy in sun or part shade in reasonably moist soil.

Persicaria amplexicaule "Rosea"

Persicaria amplexicaule ‘Rosea’

Varieties include ‘Rosea’ (pink flowers), ‘Firetail’ (white – pink flowers) and ‘Inverleith’ (deep pink flowers, much lower growing – to about 50cm tall). In the Belvedere Centre Garden ‘Rosea’ has been in flower since late August and its flower spikes have proved very attractive to honeybees.

The Beth Chatto Garden website lists several varieties of Persicaria. Other species suitable for the garden include the spreading Persicaria microcephala ‘Red Dragon’, whose leaves are lance-shaped and purplish-green. The leaf centres are purple or bronze and there is silvery v marking around the edge of the leaf. P. microcephala “Red Dragon” has round clusters of tiny white flowers in late summer and autumn.

The annual garden weed known as Redshank or Persicaria is also in the genus – it is Persicaria maculosa. The name Redshank comes from its sprawling red-jointed stems. It has spikes of small pink flowers and grows on disturbed ground and is widely distributed in Britain (see map). It is edible in small quantities (see the Plants For A Future website for more data).

When I was learning plant names Persicaria maculosa was known as Polygonum persicaria. This was part of a bigger reclassification, as the genus Persicaria has been split from the genus Polygonum in recent years, leading to a number of name changes.

Update August 2014: I have since added a third Persicaria to my list of favourites, Persicaria polymorpha or White Fleeceflower.

Spindle, Euonymous europaeus

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We’ve had a couple of frosty nights and many deciduous trees and shrubs are showing their autumn colours.

Spindle, Euonymous europaeus

Spindle, Euonymous europaeus

One of the most beautiful autumn shrubs is the Spindle, Euonymous europaeus, which has pink berries and leaves that change colour from green to a similar shade of pink before they fall. At the same time the berries split open to reveal orange seeds.

A friend e-mailed me a picture of Spindle this morning and asked me what it was, convinced that such a pretty plant must be an exotic species. But Spindle is a British native, found in hedges, scrub and open woodland mostly in the southern parts of the British Isles (see map). It is often planted, as in Earlham Cemetery in Norwich, where I photographed it yesterday. It particularly likes alkaline soils over chalk and limestone.

Earlier in the year Spindle is easy to miss and its flowers are subtle rather than spectacular, tiny greenish-yellow and borne in clusters in late spring. The flowers are attractive to many insects, including the St. Mark’s Fly, Bibio marci, a black fly that appears in swarms at the end of April. Black, with dangling legs, the fly looks a bit sinister but is entirely harmless. (See a larger than life photo of a St. Mark’s Fly on Spindle flowers here.)

Spindle is a member of the family Celastraceae, whose members are mainly tropical.

Spindle, Euonymous europaeus

Spindle, Euonymous europaeus

Spindle makes an attractive, large garden shrub for sunny or partly shaded sites, provided the soil is well-drained and not acidic. It will cope with heavy soils if they are well drained and it grows to an eventual of about 2.5 metres in height and spread. It is possible to grow Spindle from seed but the seeds need a period of warmth followed by cold to germinate. There is a cultivated variety called “Red Cascade“.

However, there are two reasons why you might not want to grow a Spindle in your garden.

Firstly, all parts of the Spindle are poisonous. The plant contain toxic glycosides. Symptoms of poisoning occur eight to 16 hours after eating and include vomiting, abdominal pain and diarrhoea. In severe cases there may be drowsiness, convulsions and loss of consciousness.  (Source: M. R. Cooper and A. W. Johnson (1988): “Poisonous Plants & Fungi – An illustrated guide”, HMSO, London). The berries are the most likely part of the plant to be eaten, though all parts of the plant have a “loathsome smell and bitter taste” which will put most people off trying.

Secondly, growers of Broad Beans should know that Spindle is one of the winter hosts of the Black Bean Aphid, Aphis fabae. The aphids overwinter as eggs and hatch in spring and subsequent generations live on the tops of Broad Bean plants, as well as on other crops and wild plants. (It is a good idea to remove the tops of broad Bean plants in late spring so that the aphids are unable to damage the plant. The tops can be steamed as a side vegetable.)

Spindle wood is fine grained and very hard. It has been used to make spindles, skewers, knitting needles and fine quality artists’ charcoal. (Thanks to the excellent blog Days On The Claise I’ve discovered that in French Spindle is called le fusain and a charcoal sketch is a dessin au fusain.) The Plants For A Future website lists other uses for the plant, including the extraction a volatile oil used in soap making from the whole plant and a bright yellow dye from the fruit and seed.