PSHB: What tree species are affected?
Trees across South Africa are under attack? Horticulturist and SALI member - Francois Malan of Brand’s Tree Felling - says he has been involved in the felling of about 30 PSHB infected trees during 2018, with box elder (Acer negundo) and oaks trees being worst hit around the Johannesburg area.
“The first signs of infection are tiny borer holes and a fine sawdust that comes out of the hole,” said Malan.
“The maples have a black ring around the hole and some trees ooze resin or gelatinous drops from the entrance holes.”
The polyphagous shot hole borer beetle or PSHB (Euwallacea fornicatus) is an ambrosia beetle native to Southeast Asia.
It was first discovered in South Africa in 2017 on London plane trees (Platanus × acerifolia) in the KwaZulu-Natal National Botanical Gardens in Pietermaritzburg.
In it's natural environment - in South East Asian countries such as Vietnam - the PSHB only attacks dead or dying trees.
Like any invasive species, the PSHB has no natural enemies in South Africa. As such, its invasion is particularly devastating for local trees.
Experts estimate that Johannesburg - one of the largest urban forests in the world - could loose up to 40% of its trees.
In 2018, the PSHB beetle was detected in dying trees found in the suburbs of Pietermaritzburg, Durban, Bloemfontein, George, Knysna and Bedfordview.
International invasion - what can we learn?
The PSHB has invaded trees across Israel - and is also found in a currently limited range on the coast of California, from Los Angeles south to San Diego.
In California, the PSHB has invaded trees in neighborhoods, avocado farms, and several public gardens.
To date, the PSHB has been known to attack plants from 58 different tree families.
Against this background, find below a list of trees that are most likely to susceptible to invasion by the PSHB in South Africa:
Indigenous South African trees:
What indigenous trees have been invaded by the PSHB ambrosia beetle and its fungus...
- Acacia (Acacia spp.)
- Bush willow (Combretum spp.)
- Yellowwood (Afrocarpus/Podocarpus spp.)
- Wild plum (Harpephyllum caffrum)
- Tree fuchsia (Halleria lucida)
- Cape willow (Salix mucronata)
- Cape chestnut (Calodendrum capense)
- Fountain bush (Psorelea pinata)
- Sweet pea bush (Podalyria caliptrata)
- Forest elder (Nuxia floribunda)
- Cross berry (Grewia occidentalis)
- Keurboom or blossom tree (Virgilia divaricata)
- Coral tree (Erythrina spp.)
Alien tree species found in South Africa:
What alien trees in South Africa are likely to be ... or have already been invaded ... by the PSHB ambrosia beetle and its fungus...
- Box elder (Acer negundo)
- Big leaf maple (Acer macrophyllum)
- Trident maple (Acer buergerianum)
- Japanese maple (Acer palmatum)
- Mimosa (Albizia spp.)
- Gum (Eucalyptus spp.)
- Holly (Ilex spp.)
- Sweetgum (Liquidambar styraciflua)
- Avocado (Persea americana)
- London plane (Platanus x acerifolia)
- Poplars (Populus spp.)
- Engelmann Oak (Quercus engelmannii)
- English Oak (Quercus robur)
- Cork Oak (Quecus suber)
- Weeping willow (Salix babylonica)
- Red Willow (Salix laevigata)
- Japanese wisteria (Wisteria floribunda)
The invasive PSHB beetle is know to invade a number of South African Invasive Species.
Whilst many conservationists may regard 'a beetle invasion' of 'a plant invader' welcome, it is important to remember that all infected trees are carriers of the PSHB and it is only a matter of time before the PSHB beetles thriving in the wood of these three invasive trees start to invade indigenous trees around them.
Invasive species that are currently being attacked by the PSHB... in South Africa:
- Castor-oil plant (Ricinus communis) - Category 2
- Mesquite (Prosopis spp.) - Category 2
- Tree of heaven (Alianthus altissima) - Category 1b
Signs and symptoms of PSHB attack?
Do you have a tree that is dying in your garden, street or suburb? What do you look for?
- Tiny beetle entry and exit holes (a bit smaller than the tip of a ballpoint pen);
- Sawdust is often found around the holes or on the ground around the trunk;
- Sometimes a sawdust “toothpick” can be seen sticking out of the beetle hole.
- In areas around the beetle holes, trees may have ‘bleeding’ symptoms (liquid oozing out of the bark);
- Look for ‘gumming’ symptoms (blobs of goo coming out of the bark) around the holes;
- Around the beetle holes, look for ‘sugar volcano’ symptoms (little cone-shaped piles of white powdery stuff on the bark).
- Branches can also be weakened by the beetles’ tunneling and break off, revealing webs of galleries filled with black fungus.
What do you do?
If you think you have a tree infected by PSBH, call a SALI landscaper.
See the SALI principle member list.