The following are the high priority exotic pests of tree nuts (including almonds, chestnuts, hazelnuts, macadamias, pistachios and walnuts) as identified in the development of the Biosecurity Plan for the Tree Nut Industry.
All would have serious consequences should they be introduced into Australia. The severity of the impact may be dependent on rootstock-scion combinations and the presence or absence of pathogen vectors.
Implementing biosecurity measures to control endemic pests will go a long way towards preventing exotic pests from entering and becoming established on your farm.
The climate of Australia would allow each of these pests to survive, establish and spread, should they be introduced. Additional information on each of these pest threats is included in the fact sheets.
For a complete list of exotic pests, see the relevant industry page on the Plant Health Australia website.
Xylella fastidiosa. Photo by Alex H. Purcell, University of California – Berkeley, Bugwood.org
Almond leaf scorch
Also known as Pierce’s disease
Bacterium – Xylella fastidiosa
Found in North and South America, and the Mediterranean
‘Burn’ zones on leaves with golden margin; causing wilted, ‘scorched’ canopy resembling salt damage; and stunted trees
Spread by sap-feeding leafhoppers or by grafting of infected planting material
Adult brown marmorated stink bug. Photo: Bugwood.org
Brown-marmorated stink bug
Insect – Halyomorpha halys
Adult is a 12-17 mm long mottled brown coloured stink bug, shaped like a shield
Very wide host range and affects many plants, including tree nuts such as hazelnut, pecan and potentially walnuts
Originally from eastern Asia, but recently introduced to North America and Europe where it is having a significant impact on agriculture and as a nuisance pest
Saliva causes significant damage to plant tissues
Eggs are cream to yellow-orange and approximately 1.6 mm long and laid in clusters on the underside of leaves
Five nymph stages that range from less than 3 mm to 12 mm long. The nymphs are orange and black when they first hatch but quickly develop a similar colouration to the adults
The adults and larvae can be confused with a number of other brown coloured stinkbugs that are present in Australia
Hitchhikes in container shipments of a range of commodities, including plant material. Adults are capable of flight allowing localised spread of the pest
Lethal canker on main stem. Image: Linda Haugen, USDA Forest Service, Bugwood.org
Chestnut blight
Fungus – Cryphonectria parasitica
Enters through wounds in the bark and grows underneath it causing a canker
Cankers are not easily seen on older thick barked trees until they crack open, exposing the buff-coloured inner bark and orange fungal fruiting structures
Eventually girdles and kills the branch above the infection point
Branch loss stimulates the tree to sprout from below the infection point or from the collar region
Can kill the tree if the trunk is girdled by a large canker or several cankers growing together
The first signs of infection are often wilting, yellowing and death of leaves and shoots. Yellow-brown to orange cankers on young smooth barked trees or branches may also be early signs of infection
The fungus is spread by animals that come into contact with the cankers and in the air after rain
Chestnut blight occurs in Japan, China, Korea, USA, Canada, Italy and throughout Europe and infects chestnut, oak, red maple, shagbark hickory and eucalypts
Image: Daren Mueller, Iowa State University, Bugwood.org
Green stink bug
Stink bug – Chinavia hilaris
Feeds on a wide range of crops including grains, fruit and nuts (including pistachio, hazelnut and almonds)
Adults are 14-19 mm long, green coloured, and shaped like a shield
The head and thorax of nymphs are black and orange when they first hatch, becoming green as they mature. Nymphs have two black coloured patches in the middle of their abdomen, which become more obvious as they mature
Could be confused with the other green coloured stink bugs in Australia, but the most obvious differences are the colour of the nymphs and the shape and colour of the adult wing covers
Any unusual stinkbug sightings in your crop should be followed up
Can spread on plant material. The adults are also capable of flight allowing for localised spread
Trogoderma granarium: Photo by Ministry of Agriculture and regional Development Archive, Ministry of Agriculture and Regional Development, Hungary, Bugwood.org
Khapra beetle
Beetles & weevils – Trogoderma granarium
Adults are small (2-3 mm long) and do not fly
Spread in infested grain
Larvae are hairy and can survive for over a year without food
Image: Natasha Wright, Florida Department of Agriculture and Consumer Services, Bugwood.org
Leaf footed bugs
The leaf footed bug (Leptoglossus clypealis), the western conifer seed bug (L. occidentalis) and the western leaf footed bug (L. zonatus)
All three species are similar in appearance and cause similar damage
Adult leaf footed bugs are approximately 19-25 mm long, brown coloured with a white band across their back. The hind legs have a widened area that resembles a leaf, giving these bugs their name
Eggs are brown coloured, rectangular and laid in a row on the leaves, fruit and nuts of the host plant.
Can spread on plant material. The adults are also capable of flight allowing for localised spread
A small 2.5-3 mm long black wasp that lays its eggs in the buds of chestnut
Egg laying induces the formation of green to rose coloured galls up to 20 mm in diameter. In cross section, small white grubs may be visible inside the gall. After the adult wasps emerge these dry out and eventually fall from the tree
Any galls on chestnut trees should be reported for diagnosis
Severe infestations can cause up to 70 per cent yield losses and in some cases the death of the tree
Considered to be the most significant insect pest of chestnuts worldwide
Can be spread by the movement of grafting material. The adults are also capable of flight allowing for localised spread
Native to Asia (china, Japan and Korea): recently introduced into the United States and Europe
Damage to a macadamia shell. Image: Vincent P Jones
Tropical nut borer
Beetles & weevils – Hypothenemus obscurus
The most important pest to macadamia production in Hawaii
It can damage up to 60% of the crop in heavily infested areas where harvesting is not strictly managed
Damage is usually seen as abundant 0.5 mm holes in the husk of the nut
Extensive tunnelling is visible throughout the husk, shell and kernel
Damaged kernels are open to further spoiling through fungal infection. The beetles are very small and up to 190 have been found in a single macadamia nut
Widespread in North America (including Hawaii), Central and South America where it attacks several tree species
Risk is from new, defoliating strains establishing to which the local cotton varieties have little or no resistance (non-defoliating strains present in Australia)
Extremely wide host range, including vegetable, fruit and broadacre crops
Leaf mottling, vascular peppering, total defoliation, boll shedding
When the stem is cut lengthways, vascular discolouration exhibits flecking of the inner tissues
Spread by spores in water, soil and infected plant material, clothing and equipment
Non-defoliating strains of Verticillium dahliae occur in Australia. The defoliating strain VCG 1A is known to occur in Australia and is currently under review
Pest of almonds, chestnuts, pistachios and walnuts
