Shot Hole Borer

Shot Hole Borer (5)

Friday, 01 November 2019 13:38

Shot hole borer invasion: SALI posters for distribution

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The South African Landscaper's Institute (SALI) is joining the battle to fight the invasive polyphagous shot hole borer (PSHB) beetle that poses a serious threat to both exotic and indigenous trees across South Africa.

The beetle is known to invade the host tree and bore holes in the branches. If undetected, it can destroy a tree within a relatively short period of time.

Adult beetles invade a variety of tree species and dig tunnels to lay eggs. The PSHB beetles then transport a fungus which attacks the tree’s vascular tissue, causing a disease called fusarium dieback (FD).

FD in turn interrupts the supply of water and nutrients to the tree. It’s known that PSHB attacks more than 300 tree species countrywide of which more than 130 of these species are susceptible to FD.

The PSHB beetle attacks a variety of tree species which include oak, most willows, plane trees, avocado, some acacias and most maples.

Reports quoting academic research show that, in other parts of the country, more than 10 000 trees have been lost which could have an adverse effect on the ecosystem and take years to replace.

Metropolitan areas such as Johannesburg and Durban as well as Pietermaritzburg, George and Knysna have lost thousands of trees.

How can you help?

    1.  Contact a SALI landscaper to advise if you have a PSHB invasion in the trees on your property.

    2.  Distribute the TWO education posters on the PSHB beetles prepared by SALI. 

Poster 1:  Are your trees dying

    Click here to download the banner:   Are your trees dying?

SALI PSHB BrochurePS

 

Poster 2:  Help STOP the spread of polyphagous shot hole borer (PSHB) beetle

    Click here to download the banner:   Help stop the spread of polyphagous shot hole borer (PSHB) beetle.

SALI PSHB StopPS

The invasive Asian polyphagous shot hole borer (PSHB) - also known as an ambrosia beetle - is a tiny black beetle the size of sesame seed (2mm).

The adult females:

  •  Carry a fungus with them from tree to tree.
  •  Burrow into a tree - 60 species have been affected worldwide.
  •  Make tunnels or galleries in the trunks and branches of the host tree.
  •  Deposit the fungus they carry, which then grows into the walls of the wood in the tunnels.
  •  Lay their eggs in the tunnels or galleries.

The fungus grows in the galleries. The adult beetles and their larvae depend on this fungus for food. 

Males are much smaller, do not fly and do not leave the galleries.

 

Symbiotic relationship

The beetles and the fungus have a symbiotic relationship - which means that these two very different species depend on each other to survive:

  • The fungus provides a ready source of food for the beetle
  • The beetle provides the fungus with a free ride to new trees.

 

Why do trees invaded by the borer beetles experience die-back or death?

Whilst the fungus feeds the beetles, the fungus is really bad for trees, as it clogs their water and food conducting tissues.

It is the maze of tunnels filled with beetles and fungus inside the trunk of the tree, together with the clogging of the arteries of the tree - that eventually kills the tree.  

 

What do landscapers 'look for' when inspecting for a shot hole borer invasion?

Signs and symptoms of PSHB attack can vary a lot depending on the type of tree. 

However this is what you need to look for:

  • Tiny beetle entry and exit holes (a bit smaller than the tip of a ballpoint pen) are usually present in the tree’s bark. 
  • 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), ‘gumming’ symptoms (blobs of goo coming out of the bark), or ‘sugar volcano’ symptoms (little cone-shaped piles of white powdery stuff on the bark). 
  • PSHB causes branches to die and can eventually kill the whole tree. 
  • Branches can also be weakened by the beetles’ tunneling. 
  • The branches break off, revealing webs of galleries filled with black fungus. 
  • The PSHB and its fungus friend can be moved in firewood. 
  • Cutting down and moving dead trees is also a vector for spreading the invasion. 

 

An academic explanation

The team at the Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria explains the life cycle of the PSHB and how it attacks your trees. 

As adult female beetles burrow into trees to establish brood galleries, they introduce the symbiotic fungus Fusarium euwallaceae which colonises gallery walls, becoming a food source for developing larvae and adult beetles (Eskalen et al., 2012; Mendel et al., 2012).

The fungus then invades tree vascular tissue, causing cambial necrosis, branch dieback and death of a broad range of trees (Eskalen et al., 2013).

 PSHB beetle life stages

If you are worried about the trees in your landscape - contact the professionals - contact a SALI member. 

 

 

Friday, 01 November 2019 13:25

Trees: A kit for identifying shot hole borer damage

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The Polyphagous Shot Hole Borer (PHSB) and Fusarium dieback is a new insect-disease complex threatening South Africa.

Up to 60 species of alien and indigenous trees are under threat, including avocado trees.

Do you have shot hole borer damage in your trees?

The team from the Forestry and Agricultural Biotechnology Institute (FABI) at the University of Pretoria have compiled a tool kit of images.

If you think you have shot hole borer, contact a SALI landscaper or arboriculturist for assistance in your area. 

Friday, 01 November 2019 13:25

Check your trees for the shot hole borer

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Are your trees dying?

Get a SALI landscaper or arboriculturist to help you with identifying the Polyphagous Shot Hole Borer in your area.

Who discovered the borer?

  • Last year, the Forestry and Agricultural Biotechnology Institute (FABI) undertook a survey of tree health in the botanical gardens of South Africa.
  • The project - entitled ‘Monitoring tree health at sentinel sites: botanic gardens and arboreta’ - was funded by the South African National Biodiversity Institute.
  • FABI is a post-graduate research institute was established in 1997, based on a recognition that the future of forestry and agriculture in South Africa.

Where did FABI first discover the problem?

  • FABI discovered the ambrosia beetle/fungal associate damaging an avenue of London plane trees (Platanus x acerifolia) in the KwaZulu-Natal National Botanical Gardens (KNNBG), Pietermaritzburg (Fig 1).
  • The polyphagous shot hole borer (PSHB)  is native to Asia.
  • Together with its fungal symbiont Fusarium euwallaceae, the borer was identified as the causal agent (Paap et al., 2018) of the significant damage to London plane trees in the KNNBG in Pietermaritzburg.

 PSHB Fig 1 Final

Fig 1. a-b. external symptoms of polyphagous shot hole borer attack on Platanus x acerifolia;   c. removal of bark and cambial tissue exposing symptoms caused by fungal colonisation associated with beetle entry hole;     d. longitudinal section through branch showing internal symptoms of discolouration around beetle gallery.

Why is this borer a problem for South Africa?

  • The PSHB is one of three cryptic species in the Euwallacea fornicatus species complex.
  • As adult female beetles burrow into trees to establish brood galleries, they introduce the symbiotic fungus Fusarium euwallaceae which colonises gallery walls, becoming a food source for developing larvae and adult beetles (Eskalen et al., 2012; Mendel et al., 2012).
  • The fungus then invades tree vascular tissue, causing cambial necrosis, branch dieback and death of a broad range of trees (Eskalen et al., 2013).
  • PSHB appears to attack trees of all age classes, the outcome varies from complete death of the tree to mild symptoms of branch dieback or sometimes no impact.
  • FABI believe this pest presents a very serious threat to the health of trees in urban, agricultural and natural environments.
  • It has become alarmingly apparent that PSHB is well established, thus has more than likely been present in South Africa for some years.

 

PSHB Fig 3 Final

Fig 2. Tree decline and death associated with polyphagous shot hole borer.    a. Quecus robur, George;   b. Acer negundo, Hurlingham Johannesburg;    c. Virgilia divaricata, Knysna;     d. Harpephyllum caffrum, Hurlingham Johannesburg and     e. Afrocarpus falcatus, Kareedouw.

 

Where in South Africa are trees being killed by the borer?

  • Since this first detection of PSHB in the KZN NBG, subsequent infestations have been confirmed in Durban, Hartswater, Bloemfontein, Johannesburg, George and Knysna.
  • The municipalities of George and Johannesburg are already facing removal of hundreds, potentially thousands of dead and dying street trees (Fig 2).
  • The suburb of Craighall Park is an epicentre of the invasion in northern Johannesburg. Entire streets of trees in Bedfordview (Talisman Rd) in Ekurhuleni are now also infected and dying.
  • It has become alarmingly apparent that PSHB is well established, thus has more than likely been present in South Africa for some years.

What tree species are affected?

  • The list of susceptible host species continues to grow.
  • Currently the list of host tree species observed in South Africa stands at around 60.
  • Confirmed highly infected tree species observed in the urban environment include Acer spp., Quercus spp. Platanus spp.
  • The growing list of indigenous tree species affected, include Erythrina spp., Combretum spp., Afrocarpus/Podocarpus spp., Harpephyllum caffrum and Vachellia spp. , Halleria lucida, Salix mucronata, Calodendrum capense, Psorelea pinata, Podalyria caliptrata, Nuxia floribunda, Grewia occidentalis and Virgilia divaricata.
  • Some of these observations come from semi-natural areas including the Garden Route Botanical Gardens (George) and Pledge Nature Reserve (Knysna).
  • In recent years, PSHB has emerged as an important invasive pest killing trees in Israel and California.
  • In these countries, it is causing significant and costly damage to urban trees, as well as presenting a major threat to the avocado industry (http://ucanr.edu/sites/pshb/).
  • In California PSHB was initially observed causing problems in urban and agricultural settings, however, as in South Africa, it has recently appeared in natural settings raising grave new concerns (Boland, 2016).

 How does the beetle spread?

  • The movement of the dead wood of infested trees - through chipping/composting, solarisation or burning – is the single biggest pathway for spread of the beetle.
  • Another potential pathway is nursery stock, we have recently observed PSHB attacking containerized trees in the nursery environment.
  • The potential for spread over long distances through the sale and movement of nursery stock is cause for serious concern (Fig 3).
  • Surveys to monitoring the spread of the beetle and fungus throughout South Africa are continuing, and chemical treatment trials and experimental trapping are planned.
  • Given the extent of the threat this pest poses to trees in urban, agricultural and natural environments, a well-developed and coordinated national action plan is required.
  • A well supported awareness campaign emphasising the risk associated with the movement of infested wood as a major pathway for continued spread of PSHB throughout the country will essential.
  • DAFF together with DEA and stakeholders have formed a Steering Committee to drive development of the action plan and awareness campaign.

Fig 4 Nursery Stock PSHB Final

Fig 3. Infested nursery stock.

 

References

Boland, J.M., 2016. The impact of an invasive ambrosia beetle on the riparian habitats of the Tijuana River Valley, California. PeerJ 4, e2141.

Eskalen, A., Gonzalez, A., Wang, D.H., Twizeyimana, M., Mayorquin, J.S., Lynch, S.C., 2012. First Report of a Fusarium sp. and Its Vector Tea Shot Hole Borer (Euwallacea fornicatus) Causing Fusarium Dieback on Avocado in California. Plant Disease 96, 1070-1070.

Eskalen, A., Stouthamer, R., Lynch, S.C., Rugman-Jones, P.F., Twizeyimana, M., Gonzalez, A., Thibault, T., 2013. Host Range of Fusarium Dieback and Its Ambrosia Beetle (Coleoptera: Scolytinae) Vector in Southern California. Plant Disease 97, 938-951.

Mendel, Z., Protasov, A., Sharon, M., Zveibil, A., Yehuda, S.B., O'Donnell, K., Rabaglia, R., Wysoki, M., Freeman, S., 2012. An Asian ambrosia beetle Euwallacea fornicatus and its novel symbiotic fungus Fusarium sp. pose a serious threat to the Israeli avocado industry. Phytoparasitica 40, 235-238.

Paap, T., de Beer, Z.W., Migliorini, D., Nel, W.J., Wingfield, M.J., 2018. The polyphagous shot hole borer (PSHB) and its fungal symbiont Fusarium euwallaceae: a new invasion in South Africa. Australasian Plant Pathology 47, 231-237.

Source: FABI, University of Pretoria. 

Friday, 01 November 2019 13:25

PSHB: What tree species are affected?

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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.

Invasive beetle

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)

Invasive trees 

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:

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.