Pests & Diseases

 

~Fungal Disease~

 

Silver leaf                                      Chondostereum purpureum                                

Silver Leaf is an aggressive live wood fungal disease that can quickly kill large healthy trees. It is easily spread, through spores infecting vulnerable, neighbouring trees. The most commonly affected trees are cherry trees and silverbirches. Other host trees include stone fruit, poplars, willows and escalonia hedges.

 

Signs of Silver Leaf are:

  • Tip die-back on healthy branches; tips browning off wilting back by   15-30cm.
  • Silver colouration on leaves.
  • Die-back of twigs to die-back of heavy structural branches.
  • In the case of well established infection, small fruiting bodies on dead branches (15-25mm across).

 

Tip die-back on cherry tree

 

 Silver colouring (pale green) on cherry tree leaves compared to healthy  green leaves from the same tree


Branch die-back on cherry tree

 

Branch die-back on silverbirch




Continual die-back after two seasons of growth
crown has less than 50% live growth



Fruiting bodies on a dead cherry tree branch



Life Cycle:

  • Airborne spores released  autumn/early winter.
  • Establishes on pruning cut, insect wound or natural opening.
  • Toxins trigger changes in leaves, manifests as silver colouration in leaves.
  • Fungi blocks conducting vessels.
  • Branches die-back.
  • Eventual plant death.

 

Control:

  • Prune out any infested branches and burn them or remove them from the property.
  • Remove any dead or infected trees that could be a possible source of the contamination.
  • Prune in  summer or early autumn if possible, when the weather is warm and dry. This is because silver leaf fruiting bodies release spores during cooler, wetter periods.
  • Larger pruning cuts can be inoculated with Trichoseal to establish the beneficial fungi Trichoderma viride on the cut. This will help prevent silver leaf spores getting established on the host tree. 
 

Trichoseal comes in powdered form and is combined with water to make a paste which is applied to pruning cuts to inoculate the area with the benifical fungi. This product is NOT classed as a pruning paste/sealer as such products are counter productive to healthy plant responses to target pruning.

 

  • If silver leaf is identified early then a biological control can be used such as trichodowls.

These are manufactured by inoculating small wooden dowels with beneficial fungal spores called Trichorderma viride which are installed into the truck of the tree. The Trichoderma will establish in the host tree and prevent the silver leaf establishing. This method is only a control and will not reverse existing damage caused by silver leaf, but it can manage it at the level of when the Trichodowls were installed. This is why it is critical to identify silver leaf disease in trees at an early stage to have any chance of saving the tree. A speciman that is infected will usually require several inoculations at yearly intervals until the signs of silver leaf have been eliminated.

 

 

 

Woodrot Fungus 

Ganoderma

Ganoderma is a saprophytic (deadwood) fungus which means it only breaks down the already dead heartwood central core of the wood tissue and does not affect the outer living sapwood. This means a stem or trunk of a tree can be infected with the ganoderma fungus and still sustain a relatively healthy canopy as the sapwood around the outside of the trunk is not damaged by this fungus. Because of this process, ganoderma can only be considered as a secondary contributing factor to the health of a tree as the primary factor will more likely be a more aggresive pathogen like phytophthora, armillaria or silver leaf fungal disease. These fungal diseases are parasitic and attack the living tissue of a plant causing sudden decline. If ganoderma gets established in a diseased tree, it may weaken the living vascular system compounding the damage of the primary infection.

 

Signs:

  • Gradual decline of tree health in the canopy ie: smaller leaf size, major deadwood in the crown.
  • Large fruiting bodies at the base of trunks/stems that can grow up to 30cm across. These plate-like fruiting bodies have a darker layered form on the upper side which can often provide a clue to the age of the fruiting body as each layer is usually associated with one years growth.

 

Control:

  • Removing the large fruiting body from the infected tree trunk may help reduce the likelyhood of re-infection through the release of spores to neighbouring specimens.
  • Tricodowels can be installed to help control the Ganoderma by introducing a benificial fungi called Tricoderma veridaeThis product is used successfully to control silver leaf disease in trees and shrubs which is a much more aggresive fungal disease. For the Tricodowls to have the maximum effect, they will need to be installed annually for approximately five years.

 

 Ganoderma Fruiting body

Although the fruiting body is quite large, it is often overlooked as it has the same appearance as tree bark and develops lower down on the trunk making it easily concealed by grass, shrubs and surrounding growth.


 wood tissue condition at ground level 

The wood tissue in the center of this Kowhai stem has been broken down by the ganoderma fungus and the tree has responded by setting up a heavy dark barrier around the decay to prevent the spread of the disease. This is a very clear example of the compartmentalization process naturally occuring in all trees and shrubs. The white wood tissue around the outside is the living sapwood of the tree which has become compromised causing the tree to gradually decline then die. 

 

 

Cypress Canker                                            Lepteutypa cupressi 

Cankers are fungal infections that cause swollen/deformed growths on branches and stems or trees and shrubs.                                               Tip growth and branches die-back as a result of water and nutrients becoming restricted due to the damage caused by the canker.              The die-back can have an adverse affect on the form of the tree by making it look very 'patchy' and untidy. Cypress canker fungi is active in wet weather when branches are infected through wounds or pruning cut.   Tiny fruiting bodies within cankers expose masses of minute spores which are spread by water splash. Mycelium within the bark becomes inactive during hot, dry weather, then reactivates once conditions are favourable for growth and infection.

 

Signs: 

  • Tip and branch die-back
  • Swollen cankerous growths on branches often oozing gum

 

Control:  

  • Prune out damaged, infected branches to help reduce the spread of infection
  • Application of a fungicide spray, especially during periods of wet weather
  • Selection of disease resistant specimens ie: Juniper chinensis 'Pyramidalis' Taxus baccata 'Fastigiata'  Thuja occidentalis

 

            Shape/form compromised by cypress canker 

 

                Tip die-back caused by Cypress Canker

 

Thuja provides a strong column form and is resistant to cypress canker

 

 Links to other common fungal diseases:

 Phytophthora Root Rot

Phytophthora Root and Crown Rot of Fruit Trees

Armillaria Root Rot

Armillaria Root Disease

disease_descriptions - Peach leaf curl

Leaf_curl

 

Links to other common Bacterial diseases:

Fire Blight damage in trees

Slime_flux

tree-diseases-wetwood 

 

 

~Insects~

 

Thrips                     

Heliothrips haemorrhoidalis

Thrips are tiny sap sucking insects, around 2-3mm long. Adult thrips are black and nymphs are cream. They are a common garden pest and host plants include: rhododendrons, azeleas, viburnums, photinia, lilly-of-the-valley, bay. Where thrips have become established on small or medium sized host plants, they can eventually cause the plant to die. Thrips will damage older leaves and then re-establish on newer leaves not allowing the plant a chance to recover. The older damaged leaves will drop off, leaving the plant looking very sparse and unwell and if left untreated, will cause the plant to decline completly until it dies.

 

Signs of Thrips are:

  • Silvering on the upper side of the leaf
  • Brown frass on the under side of leaves
  • Thin or sparse crown density

 



Life cycle:

  • Egg
  • Newly emerged larva
  • Fully grown larva
  • First resting stage (prepupa)
  • Second resting stage (pupa)
  • Adult
  • Back to egg                                           

 

Control:

  • When treating Thrips, it is important to remove accumulated leaf litter from under the plant as thrips can over-winter.                                  

  • Thrips like cool, shady conditions so pruning the crown to make it more open, in larger less affected trees, is a way of managing thrip populations as this increases light levels and air circulation.                                         

  • An effective chemical control is to spray with a systemic insecticide eg. Confidor which is absorbed into the plants vascular system and taken up by the thrips. Several applications are required as they have many generations in a short period of time. On larger plants where spraying is to difficult, the systemic insecticide can be applied to a tree band, a fabric band with plastic outer, and secured to the trunk or individual stems to allow the chemical to be absorbed through the trees bark and into the vascular system. The tree bands can be re-used to apply more chemical to get a more effective control.                 

 

Tree bands applied to stems of a large rhododendron to control thrips. Drawing pins have been used to secure the bands which allows them to be removed and chemical reapplied.


 

Puriri Moth                                    Aenetus virescens

This is our largest native moth and is most commonly found in the North Island in areas near native bush.                                                     The caterpillers can grow up to 100mm long. While the wing span of the adult male can be 100mm, adult females can be up to 150mm across. Young caterpillers bore into trunks and branches where they make a characteristic '7' shaped burrow in the wood. The caterpillers feed on the callus growth around the hole of the entrance which when active is covered by a silky, bark coloured web. This is a an effective strategy for comaflaging the entrance as it makes it very easy to overlook.             The caterpiller needs to mature for up to six years before it will be ready to metamorphosize into an elegant adult moth.                                         Once the caterpillers have left their tunnel, Wetas commonly move into this purpose built accommodation, known as a 'Weta-Hotel'.                 Healthy, established trees will be able to withstand the damage caused by the puriri moth caterpiller but smaller trees and branches can become completely ring barked by the caterpiller. This makes the host tree susceptible to die-back or breakage.

Native host plants include: puriri, ngaio, titoki, putaputaweta and kamahi while introduced plants affected are: goldern elm, ash, paulownia, maple, silverbirch, oak, poplar and willow.

 

Control:

  • There are no effective controls against puriri moth as they are completely protected by their tunnel and webbed entrance.             It would be possible to introduce an insecticide with a probe if the tunnel entrance could be located.
  • Moreporks are known to catch adult moths in flight and it is likely that most newly-hatched caterpillers exhaust their food supplies and die before finding or becoming established on their host plants. 
 

 Puriri moth damage on ash at base of trunk

Incredibly, this ash tree is able to sustain this level of damage                 and is still able to support a healthy crown showing how resilient some trees can be.
 
 
 
 
Links to other common Insect Pests:
 
 
 
 
 
 
 

 

 

~Growth Disorders~


Stem Fasciation

One of natures more quirky oddities; fasciation occurs randomly and for no apparent reason. It causes the cells at the growing point to become flattened instead of round which creates a flat, destorted stem. Fasciation is not harmful to the overall health of the tree as it usually only occurs in a few isolated points in the the crown.                                                   Common host tress are: kowhai, ngaio, cherry.


Witches Broom

These abnormal growths are caused when buds are infected with a fungal pathogen called Taphrina betulina. The resulting growth is a profusion of thick matted twiggy shoots that originate from a single growth point, creating a dense nest-like clump. These growths are not harmful to the tree and can be controlled by carefully pruning them out of the crown.

 

Burls

Burls are caused by abnormal cell growth in the cambium layer resulting in large swollen growths protruding from tree trunks. There have been no scientific studies carried out to confirm the cause of burls but it is generally understood that physical and insect damage, fungal and viral diseases are associated with the development of this growth disorder.                     Timber from burls is highly valued by wood turners and cabinet makers for it's unique, distorted grains that produce extraordinary and unique works of art.

                          Large burls on a macrocarpa in Eastbourne

 

Examples of woodturning burl wood:

Burlwood