Best practices for PSHB

A summary of strategies for monitoring, containment, and eradication. By Anna Mouton.

There are currently no registered — or even unregistered — treatments to eliminate PSHBs or their fungal symbiont from infested trees. Prevention is the only option available to growers: keep the beetles off your property. If they do show up, eradicate them.

Guidelines for monitoring and controlling the beetles are available on the Hortgro Science PSHB website. Read on for the condensed version.

Monitoring

Traps are not freely available. Growers must monitor by scouting for visual signs of infestation.

PSHBs are likely to attack preferred hosts first. Therefore, beetle activity will probably be noticeable in ornamental and windbreak trees such as English oaks, box elders, London planes, weeping willows, and beefwoods before pome- and stone-fruit trees.

Growers should identify preferred hosts on their property and visually inspect these every two weeks. If evidence of infestation is observed, the presence of PSHBs should be confirmed by an expert.

For a detailed illustrated guide on how to collect samples, visit the Hortgro Science PSHB website. Before sending samples for identification, growers should contact Hortgro at pshb@hortgro.co.za. Members of the public should contact their municipality.

How to tell if your tree has PSHB

1. Multiple round entry holes ± 1 mm diameter in trunks or branches.
2. Wet staining, gumming, or fine pale sawdust associated with the entry holes.
3. The affected tree is a known reproductive host. Click here for an updated host list.

To see photos of typical infestations in different tree species, visit the Hortgro Science and FABI PSHB websites.

Containment

PSHBs are not strong fliers, so they mostly spread with human help. Prevent introductions by keeping all untreated wood, especially firewood, off your property. This includes living plants with stem diameters greater than 20 mm.

The beetles can also spread from tree to tree along continuously wooded areas. This is another good reason to remove stands of invasive aliens such as blackwoods, castor bean plants, long-leaved and black wattles, and white and grey poplars.

Eradication

Observations suggest that PSHBs might not consider deciduous fruit trees a preferred host. But if heavily infested trees occur near orchards, spiralling beetle populations will target less-attractive trees. This is why the removal of infested reproductive host trees is critical.

Beetles start to disperse once their host is cut down, therefore infested material should be chipped as soon as possible and as small as practical — ideally to 50 mm.

Alternatively, cover any infested material with clear plastic and leave it in the sun to trap and cook the beetles. Logs or piles should be small enough to heat through. Keep covered for at least three months in summer and six months in winter.

Chipped material can also be composted to kill beetles, provided the heap heats sufficiently.

Remember that movement of infested wood spreads the beetles: untreated material should never be taken off-site.

Before moving it to a new area, clean all equipment used to process infested material to prevent spreading the beetles.