Wholesale Plant Nursery News Blog

- What will Giraffe and Kudu eat when all the trees are gone? 

We are on the brink of an ecological disaster, all because of the Shot Hole Borer Beetle. Trees are dying and FABI has indicated that natural control is not in the pipeline at this point.

Sugar Volcanoes Shot Hole Borer Beetle

What is the Shot Hole Borer Beetle

(Euwallaceae whitfordiodendron). 

The Polyphagous Shothole Borer (PSHB) - Euwallaceae whitfordiodendron, is a species of Ambrosia Beetle.  These beetles belong to the Weevil family, and get their name from the symbiotic relationship they have with ambrosia fungi.  

The adult beetles carry these fungi into the trees that they bore into, and  cultivate gardens of it for the beetle larvae to feed off of.  This species of Ambrosia beetle is miniscule – only measuring up to 2mm. The male beetle is wingless and only serves to fertilise the females. 

Shot Hole Borer Beetles in South Africa

This foreign Borer Beetle was identified in South Africa in 2017 by Dr. Tudy Paap of FABI (Forestry and Agricultural Biotechnology Institute).  As infected trees are dying, experts are listing positive identifications in towns as far-flung as Hartswater, Knysna, George, Johannesburg, Pretoria and Durban. This has severe implications for Johannesburg, one of the world’s largest urban forests with an estimated 9-11 million trees. 

Judging by the numbers of dead trees killed by Shot Hole Borer Beetles in Johannesburg and Knysna, this could become one of South Africa’s worst ecological disasters.  While the beetles are primarily encountered in towns, there is a very real possibility, that they can spread out via tree corridors and start killing trees in the veld.  

In a worst case scenario, it could also move into Zimbabwe, Zambia, Malawi and Mozambique.  The beetle and fungus has already devastated trees in California and Israel.

How Shot Hole Borer Beetles kill trees

Shot Hole Borer Beetle appears to have a cosmopolitan appetite and so far, interpolating from local and Californian reports, 33 indigenous families and 21 positively identified indigenous species could be possible targets.

The beetle carries between 3-5 fungi species with it, of which Fusarium euwallaceae (a newly described Fusarium) is the beetle grubs’ main food source and the primary vector implicated in tree deaths.  The other fungi are suspected to aid with the colonisation of a newly infected tree.

ALERT! Shot Hole Borer reproduce rapidly!

The beetle multiplies rapidly. Females lay up to 30 eggs, which take four to six weeks to mature.  The male to female ratio can be manipulated by the egg-laying female, so that more egg-producing females are produced that males.  

In KwaZulu Natal FABI has discovered that there can be up to 6 emergence episodes per year.  The implication is that if you have 1 pregnant beetle in the beginning of the season, you will have 729 million beetles by the end of the year.  In a BEST case scenario, that is 364 million females!!!!

The threat of this infestation lies in the Fusarium fungus colonising in the tree and cutting off food and water supply by mechanical blocking of the tree’s system.  Some trees will have natural resistance to the fungus, but this we will only discover as we go.

Host Trees of the Shot Hole Borer Beetle

These are trees in which the Ambrosia beetle multiplies.  Controlling infestation on these, can go a long way towards curbing outbreaks.

• Platanus acerifolium        London Plane
• Liquidambar styraciflua    Liquidamber
• Ricinus communis        Castor Oil Plant
• Jacaranda mimosaefolia    Jakaranda
• Quercus robur            English Oak
• Laurus nobilis            Laurel Tree

Obviously indigenous host trees will be identified as we go.

Indigenous Trees infected by Shot Hole Borer so far

• Harpephyllum caffrum    Wild plum
• Cussonia spicata        Kiepersol
• Cunonia capensis        Red Elder
• Diospyros lycioides        Bluebush/Monkey plum
• Acacia species – several    Thorn Trees
• Schotia latifolia            Bush Boer-bean
• Melianthus major        Touch-me-not/HoneyFlower
• Erythrina humeana        Dwarf Erythrina
• Erythrina lysistemon        Common Coral Tree
• Podocarpus falcatus        Outeniqua yellowwood
• Calpurnea aurea        Wild Laburnum

Commercial Crops Susceptible to Shot Hole Borer Beetle

• Avocado
• Macadamia
• Olive
• Peach
• Orange
• Grapes

How to identify if your trees are infected by Shot Hole Borer Beetles

This should read “How to identify die-back symptoms of Fusarium Fungus”, as it is actually the fungus that causes the damage visible on the tree.

• Wet Stains on the bark at entry/exit holes.
• Sugar volcanoes on the bark at entry/exit holes.
• Gum exudate on the bark at entry/exit holes.
• Wood frass on the bark at entry/exit holes.
• Stained wood
• Wilting
• Branch die-back
• Death

Currently there are chemical injections done by arborists, but it is expensive and will have to be repeated. There is a company working with nano-lipids which is showing great promise, we will report back within a week or two.

Controlling the rapid spread of Shot Hole Borer Beetle

• Currently cutting down and burning the wood is the only management activity managing the spread.
• Care must be taken When moving wood around in the form of fire wood and mulch because the beetle can be moved with these.
• Inspection of nurseries so that infected trees are not sold to distant locations creating new sources of infection.
• We must look at sanitation of infected wood

Please report infestations of shot hole borer

• Report to FABI - email: [email protected]
• Report to Random Harvest Nursery to email: [email protected],  together with the following information:
  • photos of:
    • Symptoms
    • Possible entry/exit wounds
  • Street address or GPS co-ordinates – pin on WhatsApp to 082 7212 478
  • Affected tree species (if you are unsure, please provide photos)
  • Your contact details
• In the meantime, as important as it is to look out for affected species, it is equally important to watch out for trees that are not affected if you are in an area of infestation. This tells us that there is something that the particular tree species produces to prevent being attacked.
• DO NOT START THROWING AROUND HEAVY CHEMICALS, apart from damaging the ecology, the penetrability of most chemicals are almost zero and it will just be wasting money.

Random Harvest Indigenous Nursery has a control for this deadly tree pest. You can read more about this in the next article in this series.

References

1. https://pubag.nal.usda.gov/download/60349/PDF
2. http://www.avocadosource.com/Journals/IABC_2012/IABC_20120814_TOC.htm
3. http://www.avocadosource.com/papers/Research_Articles/HulcrJiri2011b.pdf
4. http://ucanr.edu/sites/socaloakpests/Polyphagous_Shot_Hole_Borer/ 
5. http://www.avocadosource.com/alert_ambrosia_beetle.htm     
6. http://www.barkbeetles.info/projects_database.php          
7. http://www.avocadosource.com/                         
8. http://ucanr.edu/sites/socaloakpests/Polyphagous_Shot_Hole_Borer/    
9. http://eskalenlab.ucr.edu/handouts/pshb_symptomsandlookalikes.pdf   
10.http://eskalenlab.ucr.edu/