''Cristulariella depraedans'', commonly known as gray mold spot, sycamore leaf spot or bull's eye spot, is a fungal

pathogen In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory of d ...

that affects

maple ''Acer'' is a genus of trees and shrubs commonly known as maples. The genus is placed in the soapberry family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated si ...

trees (genus ''Acer'') and certain other woody and herbaceous

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. 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. Although fungi are eukaryotic, many pathogenic fungi are microorganisms. Approximately 300 fungi are known to be pathogenic to humans; their study is called "medical mycolo ...

''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 ''Aruncus'' is a genus of clump-forming herbaceous perennial plants in the family Rosaceae. Botanical opinion of the number of species differs, with from one to four species accepted. They are closely related to the genera ''Filipendula'' and ' ...

''), 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 Hornbeams are hardwood trees in the plant genus ''Carpinus'' in the family Betulaceae. Its species occur across much of the temperateness, temperate regions of the Northern Hemisphere. Common names The common English name ''hornbeam'' derives ...

''), dogwood (''

Cornus sanguinea ''Cornus sanguinea'', the common dogwood or bloody dogwood, is a species of dogwood native to most of Europe and western Asia, from England and central Scotland east to the Caspian Sea. It is widely grown as an ornamental plant. Description It ...

''), hazel (''

Corylus avellana ''Corylus avellana'', the common hazel, is a species of flowering plant in the birch tree, birch family Betulaceae. The shrubs usually grow tall. The nut is round, in contrast to the longer Corylus maxima, filbert nut. Common hazel is native to E ...

''), beech (''

Fagus sylvatica ''Fagus sylvatica'', the European beech or common beech, is a large, graceful deciduous tree in the Fagaceae, beech family with smooth silvery-gray bark, large leaf area, and a short trunk with low branches. Description ''Fagus sylvatica'' i ...

''), honeysuckle (''

Lonicera xylosteum ''Lonicera xylosteum'', commonly known as fly honeysuckle, European fly honeysuckle, dwarf honeysuckle or fly woodbine is a deciduous shrub. Its fruit persists for an average of 15.4 days, and bears an average of 4.5 seeds per fruit. Fruits av ...

''), bird cherry (''

Prunus padus ''Prunus padus'', known as bird cherry, hackberry (unrelated to the genus ''Celtis''), hagberry, or Mayday tree, is a flowering plant in the Rosaceae, rose family. It is a species of cherry, a deciduous small tree or large shrub up to tall. It ...

''), pedunculate oak (''

Quercus robur ''Quercus robur'', the pedunculate oak, is a species of flowering plant in the beech and oak family, Fagaceae. It is a large tree, native plant, native to most of Europe and western Asia, and is widely cultivated in other temperate regions. It ...

'') and lime (''

Tilia cordata ''Tilia cordata'', the small-leaved lime or small-leaved linden, is a species of tree in the family Malvaceae, native to much of Europe. Other common names include little-leaf or littleleaf linden, or traditionally in South East England, pry or p ...

''). 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 A sclerotium (; : sclerotia () is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant u ...

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 Fungus species