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Fraxinus angustifolia

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Common name: Narrowleaf Ash

Symptoms induced in controlled conditions (fumigation with ozone)

Fumigation of Fraxinus angustifolia with enhanced ozone levels in Open Top Chambers produced light brown interveinal stippling (picture below). Later, this stippling becomes darker.

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Fraxinus excelsior

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Common name: Common Ash

Symptoms induced in controlled conditions (fumigation with ozone)

Fumigation of Fraxinus excelsior with enhanced ozone levels in Open Top Chambers produced light brown interveinal stippling (picture below). Symptoms documented in the picture below are less severe than those sometimes observed in the field in areas exposed to high ozone levels. In these areas, a distinctive brown stippling, sometimes coalescing to cover large portions of the leaves, can be observed at the end of the growing season (August or September) (see "symptoms observed in the field").

Symptoms observed in the field

Fraxinus excelsior is the species of this genus most commonly showing ozone visible injury in the field. In the picture below, brown stippling produced by ozone is observed in the leaflets. It is recommended that the underside of these leaves should always be checked because powdery mildew may induce externally similar symptoms (see below)

In areas with high ozone levels, leaflets of Fraxinus excelsior can be almost completely covered by coalescent brown stippling, as shown in the picture below.

Symptoms observed in the field that can be mistaken for those induced by ozone

Powdery mildew can produce symptoms that can be mistaken for those induced by ozone. Look at the lower side of leaves; if white areas (hyphae of the fungus) are observed, they are indicative of the presence of this fungus. Although both ozone and powderly mildew symptoms can occur on the same leaf, it is recommended that any leaf affected by this fungus is not considered when assessing ozone symtpoms in the field.

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Fraxinus ornus

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Common name: Flowering Ash

Symptoms induced in controlled conditions (fumigation with ozone)

Fumigation of Fraxinus ornus with enhanced ozone levels in a Continuous Stirred Tank Reactor (CSTR) produced a brownish interveinal stippling.

Fumigation of Fraxinus ornus with enhanced ozone levels in Open Top Chambers light brown interveinal stippling.

Symptoms observed in the field

In Fraxinus ornus, a brownish shade like that observed in the picture below might be partly induced by ozone, but one should be cautious as this type of response might also be related to high sun radiation (indeed both agents can have a synergistic effect). In the absence of well-developed stippling, microscopic examination of the samples may be very useful for a good diagnosis.

© 2009 Fundación CEAM © 2009 Copyright of the photos: their authors