Sunday, December 9, 2007

ISA HK/China --- Tree Failure by suspected Erythrina Gall Wasps

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Dear Station Members,

This Station is broadcasting a message received & replied to a Station Member's enquiry a little while ago with all identity protected. This Station has the following comments on this received message:

1. Although the case resembled very much an attack of Erythrina Gall Wasp, it is still best to have a laboratory confirmation before an issued statement.

2. It is a public mis-conception that any tree having lots of green shining foliage would be a healthy & structurally sound tree. Many of our 'tree experts' & 'tree inspectors' in our territory would make the same mistake. If they are not convinced, they may wish to study any fallen tree or broken branches failed after storm or typhoon. Did these failed parts not bear 'green foliage of normal sizes' when fallen onto ground? Foliage is a temporary organ which actually comes & goes as part of tree physiology. Evergreen trees would also lose foliage from time to time & be replaced. Having shining foliage does not mean a tree is absolutely healthy or structurally sound. There are other factors to consider. Please refer to ETF specifications for a structurally sound tree in nursery requirement.

3. There was no storm happening when the branch failed, according to the report given by the author. Therefore, do not assume a tree or its parts would only fail in storm. It can fail by its own weight any time in calmness.

4. If the failed tree branch did hit someone or something below, the tree owner is likely to be held legally liable for personal or property damage in Civil Action. An Arborist can easily provide an Expert Witness to disclaim an Act of God, since the tree would likely be under care by somebody, being in a populated area.

If a tree is not designed, installed, maintained, inspected & assessed for risk properly, the tree is likely to become a liability rather than an asset. In any situation for a successful tree planting, it is always Mother Nature makes the rules, not us.

It is lucky that this time nobody is hurt by God's blessing. Would it happen like this the next time?

best regards,

Sammy Au
Station Manager

----- Original Message -----
From: xxx
To: Eurasian Garden Ltd.
Sent: Thursday, December 06, 2007 10:58 PM
Subject: An incident of Erythrina variegata
Dear Sammy,

I would like to bring this issue for all CA's discussion.

This is an individual of Erythrina variegata located at Mui Wo. The incident happened at about 22:00Hr, 4/12/07. The broken branch fell off from the tree suddenly onto the basketball field without obvious symptom before. This branch almost hit on a group of boys playing basketball underneath (one of the boys is my colleague's son). It is merely a luck to have nobody hurt!

Closer inspection on the cut of the broken branch identifies some small grey holes in the wood. Before it fell off from the mother tree, all the leaves seemed healthy, at least not abnormal in this deciduous season.

Is it the fall solely the act of the insect Erythrina gall wasp (Quadrastichus erythrinae Kim)?

My colleague has consulted his friend and here is his comment (just for your reference only as I haven't got permission to circulate around although I suppose it is no big deal):

I would say that this Erythrina had been seriously damaged by Quadrastichus erythrinae Kim: Common names: Erythrina gall wasp now prevalent in Hong Kong, China & South Asia.

This erythrina gall wasp inserts its eggs into the young leaf and stem tissue of the tree. The larvae then develop within the plant tissue forming galls in leaflets and petioles.

This infestation causes curling of leaves, and petioles and shoots become swollen forming many thick-walled globular galls. After feeding within the galls, the larvae pupate, and the adult wasps cut exit holes through the plant gall material to emerge. Trees with large populations of wasps within the leaves show the symtoms of having reduced leaf growth, and the plant declines in health.

Severe gall wasp infestations may cause defoliation and the death of the tree.
In addidation to this there is a seed weevil “Eurybrachys tomentosa” that lives off the decaying wood tissue left by the Erythrina gall wasp.

I am the option that it is best not to plant any Erythrina species as they age the branches are prong to snap without any apparent reason.

As the cortex layer, the outer portion of the stems of these Erythrina trees, which are bounded on the outside by the epidermis and on the inside by the endodermis thus showing no outward sign of the damage lying beneath except for the bore holes which in many cases are eventually covered by the growth of the cortex layers.

From the photo it seems that the leaves are still on the branch and the quantity is not small as being's it is now winter, yellow leaves are also normal. It's bad that I haven't had time to visit the tree or I can get more information.

I think many of our CAs may have experiences on this species and may like to share. Just discuss and study together!