Wattle gall fungal rust

Eric Frei · 19th March 2009, 08:40 PM

What is it?

Is it a gall or is it a fungi?

There wouldn't be a person in Australia who hasn't seen them, in fact some-one called it dog shit in a tree!

And that's pretty much what it looks like, it does tend to kill the host tree too.

Strange brownish to black spherical globules on wattle stems, usually the stem dies but trees can be part infected and part alive.

So I removed and dissected the above juvenile gall. For size comparison the grey timber is the top of a retaining wall post, so it's 6" wide.

As you can see from the above pictures the gall is not rotten inside, fresh tissue with this larvae living in it.

Now one could conclude rather assumptively that the larvae caused the gall. But that is not the case, the gall came first then it was "stung" as a perfect home for grubs!

So what is this "gall"?

Here comes the information ...

Quote:

This is the rust fungus gall caused by a number of species of the genus Uromycladium.

Rust Fungus Galls – Uromycladium species

The seven species of this genus occur only on acacias in Australia. Uromycladium tepperanium, the species photographed here, is the most common. It is not specific to one host but infects nearly fifty species of acacia. The infection most commonly produces reddish brown, powdery or granular, globose galls on the young stems and shoots of acacias. As a result the galls may be festooned through the outer branches of the infected plant. Locally, at Booie, many of the galls tend to take the form of thickenings of the young stems with repeated branching. In some cases the mass of infected shoots becomes quite large and heavy and weighs down the stem. The galls are woody and the globose form may occasionally grow to a considerable size - over 500g. However smaller galls may infect flowers, phyllodes, and fruits. The galls may be annual or persist for years. Old dead galls become blackened and in the case of thickened shoots quite withered.
The lifecycle of the fungus is completed on one tree with one moderately sized gall able to produce millions of minute fungal spores each able to infect another acacia.
In parts of South Africa, where Acacia saligna has been introduced and become a pest, U. tepperanium has been introduced as a biological control agent. It is slow to establish after deliberate infection but within five years has caused obvious dieback and has reduced the density of A. saligna in some areas by eighty percent (Holmes and Cowling 1997). This is a very high mortality rate and I have not seen anything like that locally though some heavy infestations and a few deaths can be seen.

The heaviest infection at Booie is in a group of fifteen cultivated A. juncifolia. All are infected, four have died and only four are managing to flower this year. A group of the same species a hundred metres away is healthy with no sign of galls. No other cultivated plants are infected. Among the locals, in some areas groups of A. implexa are heavily infected and in others A. leiocalyx is the victim. Surrounding plants are healthy or have only a few galls. Perhaps this is a matter of susceptibility.
Once a plant is infected all that can be done is cut off the infected shoots and try to improve growing conditions.
A reddish brown or rust coloured woody gall on an acacia can fairly safely be identified as a rust fungus gall. The powdery substance on the surface of the gall consists of spores and their rusty colour gives the fungus its common name. These galls are usually solid and certainly start out that way. However on cutting one up a number of insects and mites can often be found taking advantage of the food and shelter provided by the galls Even the surface can be well colonised. These secondary invaders should not be mistaken for the original cause of the gall. Associated with the galls shown were mites, moth larvae, mealy bugs and smaller numbers of other insects. Some moths and beetles breed only in rust fungus galls which is a very interesting association. They tunnel into the gall to feed but have nothing to do with producing the gall.
Once a cavity has been eaten out other insects can move in but again, these have not been involved in the production of the gall. Many of the dead, blackened galls had been almost entirely eaten away inside and only the presence of live galls on the plant indicated that the gall had been originally produced by a rust fungus.
Holmes, P.M. and R.M. Cowling. 1997. Journal of Applied Ecology 34: 317-332.

Quote:

An interesting example of a plant, animal and fungi interaction can be seen in the round galls that form on silver wattles (Acacia dealbata) and other acacias. These galls are the result of infection by the rust fungus Uromycladium tepperianum. Young, stressed trees and older, declining trees are particularly susceptible to attack from the rust fungus, which forms round galls on the stems, phyllodes (leaves) and tips of the flowering shoots. Sometimes, new galls develop on older ones. If this happens, the galls can become large, globular masses that damage branches and kill mature trees.

Recent studies in Tasmania have found that 32 species of insects, including moths, beetles and wasps, use the galls formed by Uromycladium tepperianum as a food source or refuge. Some beetles and their larvae feed on the spores that cover the outer surface of the fungus, while some insects use the tunnelled-out galls as refuges. Parasitic wasps, in turn, hunt in and around the galls. Some species of moth lay their eggs, and complete their development within the galls. These gall inhabiting moths probably have a mutually beneficial association with the fungus. The moths benefit because the galls give them protection and a food source. The fungus benefits because the moths disperse the spores when they emerge from the galls and travel to other acacias.
(Bashford 2002)

TrevMcRev · 19th March 2009, 10:16 PM

Dog shit in a tree

Next time i'm asked "whats that in my tree" at a consult i'm gonna have to resist telling them that and cracking up

TrimSolutions · 24th August 2010, 05:42 PM

Greetings...

First post, and i am dragging up old threads :P

Just wanted to add something interesting, im currently doing a assignment on "Acacia Gall Rust", The Images you show is defiantly "Acacia Gall Rust" (Uromycladium tepperianum) and it grows mainly on Acacia saligna, Looking at that image you were working on it looks like a Acacia saligna, The interesting thing about this gall is that you may or may not know but in South Africa, Acacia saligna is a major invasive weed (just like it is here in QLD :P ), to try and counter this problem the south african goverment imported "Uromycladium tepperianum" and delebritly started infecting tree's to kill them off, so that Gall we all see everywere on Acacia saligna's is being used in other parts of the world as a method of control for weeds.

Just wanted to share that tidbit...
Regards,
Scott

19th March 2009, 10:16 PM	#2
TrevMcRev Sponsor Join Date: Feb 2007 Location: Melbourne, Victoria, Australia. Posts: 1,499	Re: Wattle gall fungal rust Dog shit in a tree Next time i'm asked "whats that in my tree" at a consult i'm gonna have to resist telling them that and cracking up __________________ Total Tree Care - Melbourne Arborist Reports & Consulting,Tree Pruning & Removal \| Elm Leaf Beetle Treatment Melbourne www.treegear.com.au - Australia's Best Value Arborist Supplies FREE shipping for TREEGEAR Members-Join here

24th August 2010, 05:42 PM	#3
TrimSolutions I'm new here so be nice Join Date: Aug 2010 Location: Brisbane Posts: 1	Re: Wattle gall fungal rust Greetings... First post, and i am dragging up old threads :P Just wanted to add something interesting, im currently doing a assignment on "Acacia Gall Rust", The Images you show is defiantly "Acacia Gall Rust" (Uromycladium tepperianum) and it grows mainly on Acacia saligna, Looking at that image you were working on it looks like a Acacia saligna, The interesting thing about this gall is that you may or may not know but in South Africa, Acacia saligna is a major invasive weed (just like it is here in QLD :P ), to try and counter this problem the south african goverment imported "Uromycladium tepperianum" and delebritly started infecting tree's to kill them off, so that Gall we all see everywere on Acacia saligna's is being used in other parts of the world as a method of control for weeds. Just wanted to share that tidbit... Regards, Scott

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