Category: Disorders Plant Animal

Witches (Witch's) Broom

2/5/2016

Witches broom or little leaf disease is usually a hormone-induced growth distortion of woody plants that only affects part of the plant.

In a prior Foxypress I discussed galls that differ from the strange and miniature witches broom shoots and leaves, which are induced by insect spread viruses and phytoplasma (primitive bacteria), or fungal infection.
The image on the left shows a wandoo affected by witch's broom near the Marri picnic area.

Fasciation is an associated disorder that causes strange strap-like flattening of growing points and flowers. Images below are on canola and an isopogon.

Images below show a type of witches broom caused by A rust fungus Ceratacoma jacksoniae that affects a range of pea flowers. Images show an infection on stinkwood (Jacksonia epiphyllum). The strange red growths contain tiny reddish fruiting rods that are quite different from the powdery rust pustules that occur on our crops.

witches broom on stinkwood

strange growths containing the fruiting bodies

rod-like fruiting bodies

0 Comments

Marri decline

9/3/2016

0 Comments

Greetings fellow Foxies,
Marri trees are flowering profusely this year, possibly due to the February rains. However I have noticed a lot of red gum oozing from adult trees and a few have died spontaneously in recent years. The penny dropped when I saw beautiful adult marris in a Perth (and later Narrogin) garden with unblemished bark, in stark contrast to scabby specimens in Foxes Lair. The gum is a defence mechanism against damage by mainly woodborers.
As Foxes Lair is on the eastern edge of marri range, marris are under more water stress, slower growing, and more susceptible to parasites.

Young tree in full flower

Foxes Lair (left) and Perth garden (right) trunks

Gum flow

There are still some magnificent and ancient marris in Foxes Lair like the fire damaged specimen on the left, that still manage to produce a flower or two.
However as rainfall decreases and temperatures rise I fear that marri, jarrah and bull banksia may slowly be replaced by scrub and mallees in the reserve.

A number of factors have been suggested

Marri Canker (Quamabalaria coryecup) disease is killing marris in higher rainfall areas. Luckily I haven’t seen the characteristic symptoms here
Wildfire damage. Marri is more susceptible to fire damage than jar and wandoo. I went to an area opposite Williams Road that had marris scattered in amongst dense Dryandra nobilis scrub where the fire was most intense in 2009, and sure enough found clear fire damage. Interestingly the scars had healed with relatively little associated insect damage, and on closer observation I noticed that the scar often been affected by prior damage as there were 2 concentric scars and the exposed wood was sometimes burnt. The reserve was burnt in the 1970’s and 4WD vehicles also used to career through the bush and may have damaged trees. I also noticed that younger trees were less likely to have the scars. Regular low intensity fires that don't burn through the outer bark promote healthier trees that are more able to resist insect attack. I have recommended that scheduled cool burns in a mosaic pattern with each bay burnt every 10+ year to keep biodiversity in the reserve be included in the Foxes Lair management plan.

Probable fire damage

Possible fire damage

Secondary burn on old fire lesion

Borer damage can be easily spotted by copious outpouring of kino (red gum) from a single point, and sometimes a multiple exudations it bark splits. Kino outpours are a natural reaction from the tree to drown invading insects. Water-stressed trees are more liable to insect attack because there is less and thicker kino and it has more sugars that attract insects. The warming climate is also affecting insects’ biology by making them come out of dormancy earlier. DPAW was investigating insect damage in the reserve in the late nineties.

Copious kino from a hole

bark shaved off to show insect holes

Bullseye borer escape hole

Spontaneous splitting? DPAW colleague Peter White reminded me that gum bands occur routinely in marri wood, and that some smooth barked eucalypts have splits in their bark following large variations in rainfall.
A lot of these splits have healed.
When I shaved the rough bark back from a split, I found live flesh underneath the split with bark on either side. I have also noticed tumorous type growths on old marri branches, but suspect insect involvement.

Split and growths

bark scraped off split to show underlying growth

Growths on live and dead branch

0 Comments

Lerps and Galls

26/10/2015

Thinking that lerps were all leaf sucking insects that hid under translucent shell-shaped cases, I googled lerp to find that this refers to the sugary case, and not the insect beneath that is called a psyllid; and that psyllids also cause galls. Adult psyllids look a bit like small cicadas but are related to aphids and scale insects.
Galls develop when leaves are sucked by the juveniles, which meta morphose into adults that erupt out of the gall (remember the movie ‘Alien’?). Click here for more psyllid information.

Red galls as they mature

intact and erupted galls on lerp mallee

psyllids from lerp gall and from a lerp

A couple of months I noticed that some mallees near the Foxes Lair entry track had distorted leaves that were covered with lumpy galls. The mallee is Eucalyptus intrasylvatica, a hybrid derived from E. incrassata that is also called lerp mallee
There is a significant lerp infestation on Foxes Lair wandoos at the moment.

Sugary lerps and ants attending psyllids about to fly off

Lerp above and psyllid below

In October I saw a Honey Myrtle/ Hypocalymma angustifolium plant that was flowering but also appeared to have seed pods. The 'pods' were are actually galls.
The nightmarish looking little critter from a woody eucalypt gall is an Apiomorpha species.

Hyocalymma angustifolium galls

Some manna wattles on the Banksia walk are so heavily infested with galls that they appear to be festooned with round fruits like berries or nuts.
When I opened a few to have a look, I found maggots instead of psyllids. The maggots are larvae of the gall-midge (in actual fact a Cecidomyidae fly) that produces saliva, which forces acacias to produce gall cells. These have replaced flowers making the plant look like it has fruit.

Manna wattle galls

Fly maggot in split gall

Fly gall affected Acacia lasiocalyx flowers

Eucalyptus macrandra in the arboretum has branches severely affected by a galls on leaves and flowers that contain a small grub like those in acacia galls