''Cristulariella depraedans'', commonly known as gray mold spot, sycamore leaf spot or bull's eye spot, is a fungal pathogen that affects maple trees (genus ''Acer'') and certain other woody and herbaceous species. In maples, the foliage becomes affected by small grey lesions which expand and coalesce, the leaves later wilting and falling from the tree early. The disease seems to be associated with cool wet summers, and epidemic years sometimes occur.

Hosts

The

fungal pathogen Pathogenic fungi are fungi that cause disease in humans or other organisms. Approximately 300 fungi are known to be pathogenic to humans. Markedly more fungi are known to be pathogenic to plant life than those of the animal kingdom. The study of fu ...

''Cristulariella depraedans'' is found in Europe and North America and mostly affects trees in the genus '' Acer''. Trees affected in Germany and Britain are primarily the sycamore ('' A. pseudoplatanus'') and the Norway maple ('' A. platanoides''), while in North America the most affected are ''A. platanoides'', the red maple ('' A. rubrum''), the sugar maple ('' A. saccharum''), the silver maple ('' A. saccharinum''), the mountain maple ('' A. spicatum'') and the vine maple ('' A. circinatum''). In British Columbia it has also been reported on goatsbeard ('' Aruncus''), and in South and Central America on the bullet tree (''

Bucida buceras ''Terminalia buceras'' is a tree in the Combretaceae family. It is known by a variety of names in English, including bullet tree, black olive tree, gregorywood (or gregory wood), Antigua whitewood, and oxhorn bucida. It is native to Mexico, Cent ...

''). Studies in Germany between 1996 and 1999 extended the host range and a study published in 2000 recorded the pathogen's occurrence on 21 species of woody and herbaceous plants outside the maple group. It was shown to be present in Poland in a study lasting from 1996 to 2006, and beside ''Acer''s, the host range there included hornbeam (''

Carpinus betulus ''Carpinus betulus'', the European or common hornbeam, is a species of tree in the birch family Betulaceae, native to Western Asia and central, eastern, and southern Europe, including southern England. It requires a warm climate for good growth, ...

''), dogwood ('' Cornus sanguinea''), hazel ('' Corylus avellana''), beech ('' Fagus sylvatica''), honeysuckle (''

Lonicera xylosteum ''Lonicera xylosteum'', commonly known as fly honeysuckle, European fly honeysuckle, dwarf honeysuckle or fly woodbine is a deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and " ...

''), bird cherry (''

Prunus padus ''Prunus padus'', known as bird cherry, hackberry, hagberry, or Mayday tree, is a flowering plant in the rose family. It is a species of cherry, a deciduous small tree or large shrub up to tall. It is the type species of the subgenus '' Padus' ...

''), pedunculate oak ('' Quercus robur'') and lime ('' Tilia cordata''). It is unclear whether this increased host range is because of more intensive study or whether environmental factors have encouraged the fungus to attack new hosts.

Symptoms

The fungus develops on the surface of the leaf blades. At first there are scattered water-soaked grey spots about in diameter, but as the disease progresses, these lesions expand and coalesce and much of the leaf surface may be affected. Fruiting bodies resembling tiny white pinheads develop on either the upper or lower side (or both) of the leaf, particularly near the veins. Small black sclerotia may also form. At some stage the leaves wilt and eventually fall prematurely. In the Polish study, many of the affected host trees had characteristic pigmentation of the necrotic areas, with the centre and periphery of the lesions differing.

Disease cycle

This disease can cause slight to moderate defoliation but the tree usually fully recovers the following year. The disease is infrequent but under suitable conditions of coolness and moisture can be of epidemic proportions. It seems to be associated with cool, wet summers and mostly affects the lower branches of trees.

References

{{Taxonbar, from=Q10461699 Fungal plant pathogens and diseases Sclerotiniaceae