TDA 129 Frisia Progress
Tree Damage Alert No 129
7th Nov 2008
‘Frisia’ Progress
Love them, as many gardeners do, or hate them, as most arboriculturists do, Robinia pseudoacacia ‘Frisia’ is in trouble! In September 2007 we drew attention to symptoms of dieback (TDA 120) which appeared to be confined to young and early mature specimens of ‘Frisia’. No similar symptoms have been reported from either mature specimens of ‘Frisia’ or the true species.
This year some of the affected trees have died while others have shown some recovery growth only to dieback again. There have also been cases of a second flush of growth. Trees that have died have been reported to have foul smelling water soaked bark on the lower trunk.
It has been suggested by some arboriculturists as possibly being caused by a Verticillium species. Another explanation has been that Robinia species do not like the wet soil conditions that have been so prevalent over the last two summers.
Specimens seen by the RHS plant pathologists have shown only instances of leaf spot diseases, which can defoliate and weaken trees, Honey fungus (Armillaria species) and wood rotting fungi. The AAIS authors have been able to cut down and examine trees. The root systems of moribund trees have been found to be alive and vigorous with no signs of Honey fungus, suggesting that the dieback is from the top downwards rather than being associated with a root problem.
A symptom of Verticillium wilt is a brown stain in the annual ring, usually detectable in affected twigs that are pencil to thumb thickness. Although we have found some slight staining this has been far from a consistent feature of affected trees.
Visual evaluation of the current year’s dead and sickly shoots has revealed death of tissue around buds/leaf scars/spine groups. This appears to develop into a canker on older branches which may encircle the older twig/branch or merely extend along longitudinally.
The cause of these strips of dead tissue has not yet been established, but laboratory culturing is currently underway to establish if a pathogen is present.
Analysis of annual ring widths from three affected trees has shown consistent good growth over the past 10 years, but with a sudden and dramatic decline in 2008.
Work to identify the cause(s) of this problem will continue at AAIS and RHS. Any observations of symptoms should be sent to AAIS at Alice Holt Lodge.
Derek Patch and Brian Greig, AAIS, Alice Holt Lodge, Wrecclesham.
AAIS l Alice Holt Lodge l Wrecclesham l Farnham l Surrey l GU10 4LH
Call the Tree Helpline on: 09065 161147
Calls cost £1.50 per minute
This is one of an occasional series of Tree Damage Alerts produced for the benefit of the arboricultural profession and issued by the Arboricultural Advisory and Information Service.