Check your trees for the shot hole borer
Residents of the Overstrand have been asked to keep a watchful eye on their trees for any signs of activity by the Polyphagous Shot Hole Borer (PSHB).
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 PSHB is a tiny, invasive, black beetle that is smaller than a sesame seed and digs tunnels into numerous tree species to lay eggs and deposit fungus that block the tree’s internal transport system.
Female beetles make tunnels, or galleries, in the trunks and branches of host trees and lay their eggs inside. Males are much smaller, do not fly, and don’t leave the galleries. The females vector (or carry from tree to tree) a fungus (Fusarium euwallaceae) that grows in their galleries, and the adult beetles and their larvae depend on it for food. While this fungus definitely helps the beetles out, it is really bad for the trees and clogs their water and food conducting tissues.
Signs and symptoms of PSHB attack can vary a lot depending on the type of tree, but the 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’ tunnelling and break off, revealing webs of galleries filled with black fungus.
To date, no comprehensive solution has been found and there is no fully effective or registered treatment for either the insect or the fungus. The focus is on containment until a solution can be found.
According to botanists it is important to note the following:
• Correct disposal of infected wood is essential to curb the spread;
• Burning infected wood is not effective as the beetles fly away from the heat;
• Current pesticides and fungicides are not effective; and
• Chemical control is not effective as the beetles are deep inside the wood.
In an attempt to keep this infestation in check, Overstrand Municipality appeals to all property owners, and concerned neighbours, to check trees for signs.
Cautionary procedures should be taken when transporting or handling plants and trees. Don’t move plants that portray signs of infestations, and rather cut infected plants into smaller pieces, seal and keep them in direct sunlight. The heat from the sunlight will kill the insect and its larvae. The public can aid in the management of the spreading by reporting any signs of infestations. The Municipality is working on protocols for containment should the beetle be found in the Overstrand area.
Should any of the above symptoms be observed in trees that suggest infestation by PSHB, please report it to Horticulturist Lauren Rainbird (028 313 8972) or the Environmental Management Services Department (028 316 3724) or send an email to enquiries@overstrand.gov.za so that the necessary steps can be instituted to contain the risks.