Download Chalara `Ash dieback` - tree

Chalara ‘Ash dieback’
Wet weather has helped this disease to spread.
Symptoms of ash dieback
Ash dieback is caused primarily by the fungal disease Chalarafraxinea. The number of
infected trees in Europe has risen over the past few years, partly due to wet summer weather.
Affected trees have been found in parks, gardens, garden centres, forest stands and
commercial nurseries. The disease has contributed to the obliteration of around 90 per cent of
Denmark’s native ash tree population.
Ash trees were first recorded dying in large numbers from this form of ash dieback in Poland
in 1992. It has since spread rapidly to other European countries. It took until 2006 before the
fungus’s asexual stage, Chalarafraxinea, was first discussed as the potential culprit and in
2010 its sexual stage, Hymenoscyphus pseudo-albidus, was identified.
As a result of a pest-risk analysis and the number of confirmed cases on young imported trees
as well as established trees throughout the UK, legislation was enforced on 29 October 2012
restricting all ash imports (plants and seeds) into the UK and movement within the country
until sites have been officially inspected and given disease-free status. Northern Ireland and
the Republic of Ireland also passed similar legislation on 29 October 2012.
How to recognise it
Early stages of infection can lead to leaf drop. Late-stage infection produces crown dieback,
which can ultimately lead to the death of the tree. Chalarafraxinea has also been isolated from
the roots of symptomatic trees.
There are other disorders of ash trees that may be mistaken for Chalarafraxinea infection,
including:
• "Ash dieback" in which mature trees show severe crown dieback with new shoots being
produced lower down on the plant. This "dieback" is usually associated with root disturbance
on trees growing in arable situations.
• Stem cankers from infections by Nectriagalligena and feeding damage from the bark beetle
Leperisinusvarius, which both cause bark damage and dieback. Ash trees weakened by
infections may be more prone to bark-boring beetles.
• The activities of the ash bud moth (Prays fraxinella) in spring — moth larvae mine into the
base of shoots causing them to wilt and die.
• Physical issues including frost and drought can cause similar damage.
Symptoms
Damage can occur on all plant parts, particularly leaves, stems and large branches. At high
infection levels, the crown of an affected tree can die out and shoot regrowth can be seen
further down the plant as it tries to stay alive. Brown/black spotting can be seen on leaves
along with wilt symptoms — damage usually starts from the leaf tip downwards.
Small brown spots can be found on stems and branches (typically around the stem base) that
extend to form large cankers leading to dieback. Wood is stained brown or grey under the
canker sections and beyond into what can look like good wood.
Treatment: biological control
No specific biological controls have been identified yet.
Treatment: cultural control
Fraxinus excelsior has been found to be the most commonly affected species, with F.
‘Pendula’ and
F. ‘Jaspidea’ being particularly susceptible. Also included in that level of susceptibility are
F. mandshurica, F. nigra and
F. angustifolia. Ongoing work in Denmark and Germany suggests
that F. ‘Altena’ is more tolerant of the disease and further promising results have been
obtained in trials with
F. americana and F. pennsylvanica. It is currently thought that F. bungeana, F. ornus, F.
sieboldiana and F. texensis are also unaffected.
Researchers are still unsure of the status of F. caroliniana, F. latifolia and F. velutina.
Young plants are more vulnerable to this disease than mature specimens. However, larger
plants can be infected but symptoms tend to show through more slowly. It is unclear how the
disease spreads but local spread may be from rain splash or from insect feeding.
Long-distance spread is most likely due to the movement of diseased ash plants and the
movement of logs or wood from infected trees.
Defra’s options for destroying leaf litter — the preferred choice is listed first — include:
1 Burning material on site either on the ground (small volumes) or in mobile incinerators
(large volumes).
2 Burial in the ground
(householders only).
3 Composting. Work is ongoing into whether the spores from Chalarafraxinea will be
effectively destroyed during the composting process. In-vessel composting may provide a
more secure method because of the heat generated.
4 Incineration or landfill off site.
5 Composting off site.
Treatment: chemical control
Work in Germany has shown that products applied preventively may have some control
effect in the spring months. A 50 per cent reduction in infection occurred from applying
Torch Extra and a 66 per cent reduction in infection was found using products such as
Octave, Plover, Difcor 250EC and Switch.
Torch Extra can only be used by forest nurseries using an EAMU (2012-1680). Difcor 250EC
and Plover can only be applied to specific protected ornamentals and there is currently no
approval for use on outdoor ornamentals or forest nurseries. Products applied after plants
have been infected will provide little control — applications need to start in spring for
optimum effect.
Application before leaf fall will also help in breaking the cycle of infection in the following
spring.
The statutory instrument laid before Parliament can be downloaded at
www.dovebugs.co.uk/ashnotice.doc. Any symptoms must be reported to one of the
following:
• The Forest Research Disease Diagnostic Advisory Service
Tel: 01420 23000. Email: [email protected].
• The Forestry Commission
Plant Health Service
Tel: 0131 314 6414. Email: [email protected].
• FERA Plant Health &
Seeds Inspectorate
Tel: 01904 465625. Email: [email protected].
FERA has produced a series of videos on disease symptoms and how to take samples. See
www.youtube.com/user/FeraUK1?feature=guide