The Polyphagous Shot Hole Borer (PSHB) and its fungus in South Africa

PSHB information pamphlets  

PSHB - Information sheet   PSHB - Life stages of the beetle   PSHB - Symptoms

PSHB - External symptom types   PSHB - How to photograph for diagnosis   PSHB - How to sample

PSHB - Distribution Map     PSHB - Host Tree List    PSHB - Frequently Asked Questions

PSHB in the news

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PSHB videos

The impact of a tiny beetle and its deadly fungus on South Africa’s forests (Youtube 36 min) 

by Prof. Wilhelm de Beer, presented at the National Science and Technology Forum (NSTF) for Plant Health in South Africa on 10 June 2021

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PSHB background  

The beetle-fungus symbiosis

The discovery of this beetle and fungus in South Africa is of major concern to farmers, foresters, landscapers, home owners and ecologists, as together, these organisms can be aggressive tree killers. The PSHB is a 2mm long ambrosia beetle native to Southeast Asia. The PSHB has a symbiotic relationship with three species of fungi. These include the tree pathogen, Fusarium euwallaceae. This fungus provides a food source for the beetle and its larvae, but in susceptible trees, it kills the vascular tissue, causing branch dieback and tree death. 

In its native environment in Southeast Asia, it seems as if the beetle and fungus do not cause serious damage because tree species have evolved with the beetle-fungus complex and have resistance towards them, and because there are most likely a suite of natural enemies of the beetle. However, the beetle and fungus were somehow introduced into Israel and California in the early 2000's where they caused serious damage on several ornamental trees as well as avocado trees.

Identification of the beetle and fungus

Until December 2018 the PSHB was known as Euwallacea nr. fornicatus. However, Gomez et al. (2019) showed with DNA sequences that 'Euwallacea fornicatus' is actually a species complex including four closely related, but distinct species. These four species of Shot Hole Borer are very similar in shape, and can only be distinguished by specialists under a microscope or with DNA sequences. The four species carry different fungal species, have different host ranges, and different geographical distributions (Gomez et al. 2018). Although they suggested the name Euwallacea whitfordiodendrus should be used for the PSHB, this was an error that was corrected in a subsequent paper by Smith et al. (2019). The correct names of four Shot Hole Borer species in the E. fornicatus complex are:

1. Tea Shot Hole Borer A [TSHB-a = Euwallacea perbrevis (Schedl 1951)]

{Distribution: Asia (American Samoa, China, Indonesia, Papua New Guinea, Samoa, Sri Lanka, Taiwan, Thailand), Australia, and introduced in the USA (Florida and Hawaii)}

2. Tea Shot Hole Borer B [TSHB-b = Euwallacea fornicatior (Eggers 1923)]

{Distribution: Asia (Malaysia, Papua New Guinea, Singapore, Sri Lanka)}

3. Polyphagous Shot Hole Borer [PSHB = Euwallacea fornicatus(Eichhoff 1868), previously referred to as Euwallacea nr. fornicatus and Euwallacea whitfordiodendrus (Schedl 1942)] 

{Distribution: Asia (China, Hong Kong, Japan, Taiwan, Thailand, and Vietnam) and introduced in USA (California), Israel, and South Africa} 

4. Kuroshio Shot Hole Borer [KSHB = Euwallacea kuroshio Gomez and Hulcr 2018]

{Distribution: Asia (Indonesia, Japan, and Taiwan) and introduced in Mexico and USA (California)}

To date, only the PSHB has been found in South Africa. However, both the PSHB and KSHB have invaded California, while TSHB-a has invaded Florida. These species carry similar fungi, have similar life styles and similar effects on trees. With our borders being open for trade to Southeast Asia, the risk that one of the other species can be introduced is very high. Co-occurring species increase the chances for interbreeding which will enhance the adaptability of the beetles to new hosts and new environments, posing a greater threat. From a management perspective, they are dealt with in the same ways. In California they have thus started referring to the PSHB and KSHB jointly with the single term Invasive shot hole borers (ISHB). It is recommended that for management and legislative purposes we also adopt the term ISHB in South Africa.

A large diversity of host trees

'Polyphagous' refers to the ability of the PSHB to infest many different tree species. In California, surveys in botanical gardens revealed that more than 200 tree species have been infested, damaged and often killed, by these organisms (Eskalen et al. 2013). An important distinction is being made between different types of infestations. Reproductive host trees are trees that the beetle infests and where it successfully establishes a breeding gallery in which the fungus grows, where eggs are laid, and larvae develop into mature adults, thus completing its life cycle. The majority of reproductive hosts eventually succumb to the disease symptoms caused by the fungus. Non-reproductive host trees are attacked by the beetle, but the beetles do not establish breeding galleries. The fungus may, or may not cause disease. Trees are generally not expected to die.

A problem when compiling these lists is that sometimes PSHB can infest a stressed tree (e.g. as result of drought, too much water, root damage, etc.). Such an individual, stressed tree might then become a reproductive host, whereas healthy growing individuals of the same species are barely affected. When trees are assessed for Fusarium Disease or whether it is a reproductive host, other stress factors on the tree should always be considered.

The invasion in South Africa

Since its discovery in KwaZulu-Natal in 2017, the FABI team has confirmed the presence of the PSHB in eight of the nine provinces in South Africa. The only exception as of March 2021 is Limpopo, but that might merely be because appropriate samples have not been received from that province. Below is a list of all the host trees in South Africa on which the presence of the beetle and/or fungus have been confirmed with DNA sequences in FABI. 

Based on the experiences in California and Israel, avocado trees are among the most susceptible agricultural crop trees to PHSB infestation and FD. To date, PSHB has been found on some backyard avocado trees in Sandton and Knysna, but its presence has not yet been confirmed in any commercial orchards in South Africa (van den Berg et al. 2019). PSHB has been detected in pecan and macadamia orchards, but effects seem to be limited on these crops at the moment, most likely as these do not seem to be reproductive hosts Other fruit trees in private gardens on which PSHB has been detected include lemon, orange, guava, peach, and grapevine. However, at this point, there is no evidence suggesting that PSHB pose a threat to these crops, but producers should carefully monitor and report any infestations.

In addition to agriculture, commercial forestry is another sector that is concerned. PSHB infestations have been observed on a small number of roadside wattle trees – but to date, no trees in commercial plantations have been infested. Based on observations on Acacia spp. from commercial forestry in SE Asia, however, there is concern around the threat posed to species of importance to the South African forestry industry.

The most visible impact of the PSHB invasion in South Africa is in urban forests on street, park and garden trees, and this became the focus of many articles in the media. Many trees have been killed by PSHB in Sandton, George, and Knysna, while reports from Sedgefield, Bloemfontein, the Ekhurhuleni metro, Jankempdorp, Hartbeesfontein, Pietermaritzburg and Durban suggest that the impact is becoming worse in those areas. The most common trees to be killed are English oak, Chinese maple, Japanese maple, boxelder and sweetgum.

Of great concern is the recent discovery of PSHB on London plane and sweetgum in Somerset West in the Cape Peninsula. With the major impact of the disease on oak trees in especially the George and Knysna areas, it is inevitable that the famous oaks of Stellenbosch and the surrounding wine farms will be dramatically impacted.

Most unpredictable is the impact that the PSHB invasion will have on our native forests. Several native tree species were found to be infested in the gardens of Sandton, George and Knysna, with species like the coral tree, keurboom and Cape willow being particularly vulnerable and often killed. It is now known that the beetle is spreading from the urban areas into native forests close to the towns of George, Knysna and Durban. However, which species will be affected and to what extent, is unpredictable.

The PSHB Research Network

PSHB as an invasive is relatively new to science, and has only been studied since the outbreaks in California and Israel in the early 2000s. There are thus many unanswered questions about this pest that is essential to understand to be able to better reduce its impact. The research team at FABI is engaging with various government agencies, municipalities and industries to advise on policy and strategy, and to secure funding for research projects. In the process they have established a research network including academics from seven other universities who will collaborate on various aspects of the PSHB invasion in the different regions.

Projects that are fully funded at present include the monitoring and impact on avocados (Prof. Noelani van den Berg), macadamias (Dr Gerda Fourie), pecans (Prof. Wilhelm de Beer), botanical gardens (Dr Trudy Paap and Dr Mesfin Gossa), and forestry crops (Dr Trudy Paap and others from the Tree Protection Co-operative Programme (TPCP) and biological control (Prof Brett Hurley).

Other ongoing projects include an assessment of the impact of PSHB on native trees and forests in the southern Cape and KwaZulu-Natal (Prof. Wilhelm de Beer, Dr Trudy Paap, Prof Francois Roets [Stellenbosch University], and Prof Martin Hill [Rhodes University]).

The team appreciate the funding from the Department of Environment, Forestry and Fisheries (DEFF), SAPPA, SAMAC, Hans Merensky Foundation, DSI NRF Centre of Excellence in Plant Health Biotechnology, SANBI. 

What can be done?

There is no way in which the PSHB invasion in South Africa can be stopped. However, some treatments and management strategies can reduce its impact.

Municipalities should:

• Train staff to recognize and cut down heavily-infested reproductive host trees from streets and public areas.
• Infested branches can be cut if the main stem is not infested (unlikely, as PSHB usually infests the stem first).
• Designate dedicated dumping sites where infested wood can be dumped as it poses a risk of spreading the beetle.
• Chip wood to pieces finer than 5cm at the dumping sites.
• Provide a help desk (preferably online) where the public can report infested trees and get information.

Tree growers/home owners should:

• Try to determine whether the symptoms are really caused by PSHB (see FABI brochures).
• If unsure, ask help from municipal or other help desks, or your local arborist.
• If the tree is a heavily-infested reproductive host, cut it down.
• Infested branches can be cut if the main stem is not infested (unlikely, as PSHB usually infests the stem first).
• Dump the wood at a dedicated (by your municipality) dumping site.
• Chip the wood to finer than 5cm, allow chips to compost by keeping it wet.
• Or burn the wood on site (some beetles will fly away when the wood becomes hot or when smoke appears, so do not burn in uninfested areas).
• DO NOT MOVE FIREWOOD AROUND, ESPECIALLY NOT OUT OF THE INFESTED AREA WHERE YOU LIVE.
• Or solarize (leave in full sun) chopped wood under thoroughly-sealed clear plastic sheets for at least one month in summer or several months during winter.
• At present no chemical product is registered (legal) to use on PSHB in South Africa.

PSHB enquiries

Western Cape: fill in the online report form at www.capetowninvasives.co.za 

Johannesburg: email trees@jhbcityparks.com or Whatsapp: 0828030748

Other parts of the country, especially from towns where it has not been reported, and host tree species not on the list below: email pshb@fabi.up.ac.za (English please, some of our staff are foreigners who do not speak Afrikaans)

PLEASE DO NOT SEND SAMPLES TO FABI WITHOUT FIRST CONTACTING US AT pshb@fabi.up.ac.za

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PSHB host list¹ 

(Download list here) (Last updated 2021-07-06)

REPRODUCTIVE HOST TREES²

Exotic species:

Acacia longifolia (long-leaved wattle); Acacia mearnsii (black wattle); Acacia melanoxylon (blackwood); Acer buergerianum (trident (Chinese) maple); Acer negundo (boxelder); Acer palmatum (Japanese maple); Acer saccharinum (silver maple); Brachychiton discolour (pink flame tree); Casuarina cunninghamiana (beefwood); Gleditsia triacanthos (honey locust); Liquidambar styraciflua (American sweetgum); Magnolia grandiflora (southern magnolia); Persea americana (avocado); Photinia x fraseri (Christmas berry); Platanus x acerifolia (London plane); Populus alba (white poplar); Populus x canescens (grey poplar); Populus nigra (Lombardy poplar); Populus simonii (Chinese cottonwood); Quercus palustris (pin oak); Quercus robur (English oak); Quercus suber (cork oak); Ricinus communis (castor bean); Salix alba (white willow); Ulmus parvifolia (Chinese elm); Viburnum odoratissimum (sweet viburnum), Wisteria sinensis (Chinese wisteria).

Native SA Species:

Afzelia quanzensis (pod mahogany); Anisodontea scabrosa (rough-leaf African mallow); Bauhinia galpinii (pride of de Kaap); Brachylaena discolor (coast silver oak); Calpurnia aurea (wild laburnum); Combretum erythrophyllum (river bushwillow); Combretum krausii (forest bushwillow); Diospyros glabra (Cape star-apple); Erythrina caffra (coastal coral tree); Kiggelaria africana (wild peach); Podalyria calyptrata (water blossom pea); Psoralea aphylla (leafless fountain bush); Psoralea pinata (fountain bush); Salix mucronata (Cape willow); Sparrmannia africana (African hemp); Trema orientalis (pigeon wood); Trichilia emetica (Natal mahogany); Vepris lanceolata (white ironwood); Virgilia oroboides subsp. ferruginea (keurboom).

NON-REPRODUCTIVE HOST TREES³

Exotic Species

Bauhinia purpurea (butterfly orchid tree); Betula pendula (silver birch); Bougainvillea sp. (bougainvillea); Camellia japonica (common camelia); Carya illinoinensis (pecan nut); Ceiba pentandra (kapok); Cinnamomum camphora (camphor); Citrus limon (lemon); Citrus sinensis (orange); Diospyros kaki (persimmon); Eriobotrya japonica (loquat); Erythrina livingstoniana (aloe coral tree); Eucalyptus camaldulensis (river red gum); Ficus carica (common fig); Fraxinus americana (American ash); Fraxinus excelsior (European ash); Hakea salicifolia (willow-leaved hakea); Hibiscus rosa-sinensis (hibiscus); Jacaranda mimosifolia (jacaranda); Macadamia sp. (macadamia nut); Malus domestica (apple); Melia azedarach (syringa); Metasequoia glyptostroboides (dawn redwood); Morus nigra (black mulberry); Olea europaea subsp. europaea (cultivated olive); Platanus occidentalis (American plane); Platanus racemosa (Californian plane); Plumeria rubra (frangipani); Prunus avium (sweet cherry); Prunus cerasifera (cherry plum); Prunus nigra (black plum); Prunus persica (peach); Psidium guajava (guava); Quercus rugosa (net leaf oak); Robinia pseudoacacia (black locust); Salix babylonica (weeping willow); Schinus molle (pepper tree); Solanum mauritianum (bugweed); Taxodium distichum (swamp cypress); Ulmus minor = Ulmus procera (English elm); Vitis vinifera (grape vine).

Native SA Species:

Adansonia digitata (baobab); Afrocarpus falcatus (Outeniqua yellowwood); Albizia adianthifolia (flat crown); Buddleja saligna (false olive); Calodendrum capense (Cape chestnut); Celtis africana (white stinkwood); Commiphora harveyii (copper stem corkwood); Cordia caffra (septee tree); Cussonia spicata (cabbage tree); Diospyros dichrophylla (star apple); Diospyros lycoides (monkey plum); Diospyros whyteana (bladdernut); Dombeya rotundifolia (wild pear); Dovyalis caffra (kei apple); Ekebergia capensis (Cape ash); Erythrina lysistemon (common coral tree); Ficus natalensis (Natal fig); Ficus sur (Cape fig); Grewia occidentalis (cross berry); Gymnosporia buxifolia (spike thorn); Halleria lucida (tree fuschia); Harpephyllum caffrum (wild plum); Ilex mitis (Cape holly); Leonotis leonurus (wild tobacco); Melianthus major (honey flower/Kruidjie-roer-my-nie); Nuxia floribunda (forest elder); Olea europea subsp. africana (wild olive); Olinia ventosa (hard pear); Osteospermum moniliferum (bietou); Podocarpus henkelii (Henkel’s yellowwood); Protea mundii (forest sugarbush); Prunus africana (red stinkwood); Rapanea melanophloeos (Cape beech); Schotia brachypetala (weeping boerbean/huilboerboon); Searsia chirindensis (red currant); Searsia lansea (karree); Senegalia burkei (black monkey-thorn); Senegalia (Acacia) galpinii (monkey-thorn); Syzygium cordatum (waterberry); Vachellia (Acacia) karroo (sweet thorn); Vachellia (Acacia) sieberiana var. woodii (paper bark thorn); Virgilia divaricata (keurboom).

¹ Only tree species on which the presence of the beetle and/or Fusarium fungus have been confirmed with DNA sequences are listed here. 

² Host trees in which both the beetles and the fungus establish, and where the beetle successfully reproduce. In most cases the reproductive hosts will eventually be killed by the fungus.

³ Host trees that are attacked but the beetles do not establish breeding galleries. The fungus may, or may not cause disease. Trees are generally not expected to die.

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PSHB distribution in South Africa

(Download map here) (Last updated 2021-07-06)

EASTERN CAPE: Kaukamma (Storms River; Tsitsikamma Falls); Makana (Makhanda - Grahamstown); Ndlambe (Port Alfred); Buffalo City (East London)

FREE STATE: Mangaung (Bloemfontein)

GAUTENG: Ekurhuleni (Bedfordview); City of Johannesburg (Region A: Lanseria, Midrand; Region B: Craighall Park, Hurlingham, Randburg; Region C: Roodepoort; Region D: Soweto); Tshwane (Daspoort, Rietondale Park)

KWAZULU-NATAL: eThekwini (Buffelsdraai, Durban, Durban North, Gillets, Kloof, Scottburgh, Umhlanga); KwaDukuza (New Guelderland, Shaka's Rock); Msunduzi (Pietermaritzburg); Umdoni (Pennington); uMhlathuze (Felixton); Ray Nkonyeni (Umzumbi)

MPUMALANGA: Mbombela (Nelspruit)

NORTHERN CAPE: Frances Baard (Jan Kempdorp)

NORTHWEST: Dr Ruth Segomotsi Mompati (Greater Taung); Matlosana (Hartbeesfontein)

WESTERN CAPE: Bitou (Greater Plettenberg Bay, Harkerville Forest); George (George, Wilderness); Knysna (Knysna, Sedgefield); City of Cape Town (Somerset West)

 

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PSHB Frequently Asked Questions

(Downlaod FAQ document)

 

What is the Polyphagous Shot Hole Borer (PSHB)?

- Background information on the PSHB 

- Life stages and sexes of the PSHB 

 

What is the difference between the Polyphagous shot hole horer (PSHB) and Invasive shot hole borers (ISHB)?

The Polyphagous Shot Hole Borer [PSHB = Euwallacea fornicatus] is one of four closely related species. The other three species are:

- Tea Shot Hole Borer A [TSHB-a = Euwallacea perbrevis]

- Tea Shot Hole Borer B [TSHB-b = Euwallacea fornicatior]

- Kuroshio Shot Hole Borer [KSHB = Euwallacea kuroshio]

To date, only the PSHB has been found in South Africa. However, both the PSHB and KSHB have invaded California, while TSHB-a has invaded Florida. These species carry similar fungi, have  similar life styles and similar effects on trees. From a management perspective, they are dealt with in the same ways. In California they have thus started referring to the PSHB and KSHB jointly with the single term Invasive shot hole borers (ISHB).

 

I think my trees are infested with PSHB, how can I know for sure?

The entrance holes of PSHB are about 1 mm in diameter. This is approximately the size of the tip of a ballpoint pen or toothpick. The holes are perfectly round (never oval). 

You can compare the symptoms on your trees with the following photographs:

- General symptoms of PSHB attack and the disease its fungus causes in trees 

- Variety of PSHB attack symptoms on different tree species 

 

What does the PSHB look like?

If you found beetles on your tree(s), compare them with these photographs:

- PSHB life stages 

- Note: the PSHB beetle is only 2 mm long.

 

I found a beetle larger than 2 mm in my trees. What is it?

Many other larger beetle species bore into dead and dying trees, but these are usually secondary, and not the cause of tree death. The PSHB is one of only a few insects that will bore holes into living stems or branches of trees.

 

I am still not sure if I have found PSHB, who can help me with identification?

You can send photographs of the infested trees to the FABI diagnostic team, but to assist you we need a specific set of photographs and some basic information. 

• Please follow these instructions when taking photographs
• Please provide the tree species (if known) and location (name of the town, if possible the exact address).
• Send the photos by email to: pshb@fabi.up.ac.za (English please, some of our staff do not speak the other South African languages)

 

Should I send a sample of PSHB or the infested tree to FABI?

PLEASE DO NOT SEND, POST OR COURIER LIVING BEETLES TO US WITHOUT DISCUSSING IT WITH US FIRST, AS THEY CAN EAT THROUGH PAPER AND PLASTIC. WE DO NOT WANT TO SPREAD THE BEETLE AROUND THE COUNTRY!

We shall request you to provide a sample for confirmation only when the tree species in question is not on the current host tree list, or is in an area where the beetle has not been found before (current distribution in South Africa). 

• Instructions on how to prepare a sample. 
• Please fill out this sample information sheet with as much information as is available, print and include with the sample, and email it to diagnostic.clinic@fabi.up.ac.za 

 

What is the difference between reproductive and non-reproductive host trees?

The PSHB can attack many species of trees. However, it is not able to breed and multiply on all these tree species.

- Reproductive hosts: trees in which both the beetle and the fungus establish. The beetles construct galleries (tunnels) and breed successfully. In many cases reproductive hosts will eventually die.

- Non-reproductive hosts: trees that are attacked by the beetle, but in which the beetles do not establish breeding galleries. The fungus may, or may not cause disease. Trees are generally not expected to die.

What is a ‘heavily infested’ reproductive host tree?

A tree is considered to be a heavily infested reproductive host if PSHB is actively breeding throughout the tree. You will see many entrance and exit holes, with other signs such as frass or noodles indicating extensive beetle activity. Once a susceptible reproductive host tree becomes heavily infested, it is generally not expected to survive.

 

What species of trees are attacked by PSHB?

An updated list of confirmed host trees in South Africa. Tree species are only added to this list if the identity of the beetle and/or the fungus was confirmed in our laboratories by means of DNA sequencing.

 

In which parts of South Africa has the presence of PSHB been confirmed?

Map of confirmed locations in South Africa. Localities are only added to this list if the identity of the beetle and/or the fungus was confirmed in our laboratories by means of DNA sequencing.

EASTERN CAPE: Kaukamma (Storms River; Tsitsikamma Falls); Makana (Makhanda - Grahamstown); Ndlambe (Port Alfred); Buffalo City (East London)

FREE STATE: Mangaung (Bloemfontein)

GAUTENG: Ekurhuleni (Bedfordview); City of Johannesburg (Region A: Lanseria, Midrand; Region B: Craighall Park, Hurlingham, Randburg; Region C: Roodepoort; Region D: Soweto); Tshwane (Daspoort, Rietondale Park)

KWAZULU-NATAL: eThekwini (Buffelsdraai, Durban, Durban North, Gillets, Kloof, Scottburgh, Umhlanga); KwaDukuza (New Guelderland, Shaka's Rock); Msunduzi (Pietermaritzburg); Umdoni (Pennington); uMhlathuze (Felixton); Ray Nkonyeni (Umzumbi)

LIMPOPO: No confirmed reports to date.

MPUMALANGA: Mbombela (Nelspruit)

NORTHERN CAPE: Frances Baard (Jan Kempdorp)

NORTHWEST: Dr Ruth Segomotsi Mompati (Greater Taung); Matlosana (Hartbeesfontein)

WESTERN CAPE: Bitou (Greater Plettenberg Bay, Harkerville Forest); George (George, Wilderness); Knysna (Knysna, Sedgefield); City of Cape Town (Somerset West)

 

How does the PSHB kill trees?

As adult females bore into trees to establish breeding galleries, they introduce the fungus Fusarium euwallaceae, which colonises gallery walls. The fungus is cultivated as a food source for developing larvae and adult beetles, but it invades and kills the tree’s vascular tissues, preventing sap flow. This can lead to branch dieback and tree death. 

 

I have confirmed PSHB is attacking trees on my property. What should I do now?

Treatment or removal of infested trees on private land is the responsibility of the landowner. Firstly, try to determine whether or not your tree is a reproductive host and how severely it is infested.  This will determine which action should be taken. 

 

If the tree is a heavily-infested reproductive host (list of reproductive hosts), cut it down. If you are unsure, your local arborist might also be able to advise. 

• If the main stem is not infested, only the infested branches need to be removed. (But this is unlikely, as PSHB usually infests the stem first).
• Preferably treat the cut wood on site in one of the following ways:
• Chip the wood (if possible to finer than 5cm), and allow chips to compost by keeping the heap wet.
• OR burn the wood on site if fire is permitted in the area where you live. Some beetles will fly away when the wood becomes hot or when smoke appears, so do not burn wood in uninfested areas.
• OR solarize (leave in full sun) chopped wood under thoroughly-sealed clear plastic sheets for at least one month in summer or several months during winter.
• If the wood has to be removed from the property, dump the wood at a dedicated dumping site (contact your municipality to find out where such a site is) .
• DO NOT MOVE FIREWOOD AROUND, ESPECIALLY NOT OUT OF THE INFESTED AREA WHERE YOU LIVE.

 

If the tree has only a few beetle holes, and no signs of further activity after the initial attacks are seen, it is most likely a non-reproductive host (list of non-reproductive hosts).

 

Do I really need to cut my tree down?

The removal of heavily infested reproductive host trees is considered an important strategy to reduce the number of beetles in the environment. Heavily infested reproductive hosts become a major source of large numbers of beetles, which increases the risk of adjacent trees being infested, and the likelihood of PSHB spreading to new localities. Removing these heavily infested trees reduces the risk of unchecked beetle spread.  Importantly, after the removal of an infested tree, the material has to be disposed of appropriately to reduce beetle survival and spread. 

 

I have confirmed PSHB is infesting trees on government land. What should I do now?

Inform the relevant authority. Trees on municipal land (e.g. streets and city parks) are the responsibility of the municipality, and may not be removed without their permission. Trees on other government property (e.g. nature reserves) are managed by a variety of provincial and national government bodies (e.g. SANParks, CapeNature, Ezemvelo KZN Wildlife). Some of these authorities have put reporting structures in place. The ones of which we are aware, are listed here:

Western Cape: fill in the online report form at www.capetowninvasives.co.za 

Johannesburg: email trees@jhbcityparks.com or Whatsapp: 0828030748

Other municipalities: contact the Parks, Garden or Environment section of the relevant municipality.

For parks or protected areas: report to the appropriate government structure.

 

Are there any chemicals that I can use to treat my trees?

At present no chemical product is registered (legal) to use on PSHB in South Africa. However, control of light infestations on trees may be achievable by direct injection of insecticides and fungicides. Studies from California show combinations of the insecticides emamectin benzoate and bifenthrin and fungicides, including propiconazole, can reduce infestation, especially when applied during early stages (Mayorquin et al. 2018; Grosman et al. 2019). Chemical control of PSHB in more heavily infested trees, however, seems unattainable (Mayorquin et al. 2018). Chemical treatments are currently being investigated in a South African context. While some of these may prove effective, applying these in natural settings will not be feasible.

(PSHB webpage last updated 2021-07-15)

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Other online resources

University of California resources   California host tree list    California information brochures

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