By David Goldney
A native of Europe, the elm leaf beetle was first found in Australia in 1989, along the Mornington Peninsula. In Victoria. Approximately the size of a large grain of rice, the elm leaf beetle appears dull green in colour early in the season, with the colour becoming more defined as the season progresses. Elm leaf beetles hibernate over the winter period in dry sheltered places such as under tree bark and around buildings etc. Activity begins in spring as temperatures rise with beetles emerging and feeding on young elm leaves and new sucker growth. As the season advances beetles start laying small eggs in a double row, the colour and appearance of mini lemons, approximately the size of a sesame seed. Hatching begins in 7-10 days depending on temperature, with larvae resembling small black specks. Larvae (caterpillar like) have three moults – and grow significantly between the first and third moult. Beetle larvae feed on the leaves of elms by eating the green matter out, leaving a skeleton of veins that desiccates leaves. This is the cause of complete canopy defoliation. The most severe damage is done after the third moult, with larvae consuming 18 times more leaf material compared to the first moult stage. Late in the third moult stage, the larvae begin to migrate down the trunk, or drop out of the canopy to the ground, where they pupate either on the ground or in crevices in the bark of the lower trunk. After about 10 days, temperature dependent, new beetles emerge from the pupae and the new generation disperses. and the cycle continues. In Australia, we now know that up to 4 generations of beetle breeding can occur over the spring-summer period.
Buildings located near heavy infestations of elm leaf beetles often suffer the immigrations of overwintering beetles, or second or third generations invasions as the current infestation appears to be, often in plague proportions. Infestations can be greater when strong winds dislodge adults and larvae (caterpillar-like stage) who then seek shelter nearby.
Prior to periods when beetles move to nearby buildings, sealing all cracks that allow entry, caulking areas around window moulding, and minimizing entry points at door openings is an effective control measure. Screens should be in place where windows can be open and shut. Some increase in control is possible if sealing is accompanied by spot insecticide treatment of the building exterior. Several household formulations of pyrethroid insecticides containing permethrin, bifenthrin and related compounds are available for this use from nurseries and similar outlets.
Regular vacuuming is most effective for beetles that are found within a building. This is best done during warm periods when most of the beetles are active and mass on windows or walls. During cooler periods, the overwintered beetles often return to sheltered areas.
Elm leaf beetles do not reproduce in buildings nor do they feed on household foods and furnishings. However, they can leave yellowish stains on walls and curtains. Although they are periodically active, overwintered beetles, or as in this case, second or third generation spring-summer beetles, the nuisance problems, whilst often severe, will end by autumn, after all beetles have gone outdoors or died as the temperature drops.
Consecutive generations of beetle can continue to feed well into the first week of May, depending on temperature and the nutritional quality of the leaf.
The best practice control of this beetle with few natural enemies in Australia, is usually regarded as stem injection of an appropriate insecticide into infected trees implemented by an experienced professional. Soil injection is very effective but generally avoided because of adverse environmental outcomes. Those chemicals used in Australia have mostly been banned in Europe because of their collateral impact on bees. Native bees do not usually show much interest in Elm trees. Bathurst Regional Council generally accepts responsibility for treating elm trees on its land, but not on private land. Not for profit groups would usually find great difficulty in raising the capital needed for the three-year injection cycle.
Specific Notes on the Perthville UCA Elm Beetle Infestation
The source of the beetles is almost certainly from infested elm trees along the Vale Road mainly on the Perthville section. There are no elm trees within the grounds of the UCA. Some elm trees on the Vale Road are seemingly immune to Elm Tree Beetle attack whilst others are heavily infested. Elm tree age varies from around 60 – 100 years to young saplings struggling to survive intense competition from fellow elms. Most understory trees are around 10-20 years old and growth locked.
Live and dead adult beetles were located this morning (31/01/2017) at the entrance doors of church and hall, but no larvae. Less were found on external window sills. No larvae were in these positions. The photo in The Western Advocate on 31st Jan 2016, identifies hundreds of adults on an internal window sill of the church. These can only have accessed this space by entering via openings around windows and/or openings around the pair of external double doors. Given that adults are not particularly good flyers, it is possible that recent wind gusts have blown the beetles into the church yard from infected trees, and they have then sought shelter in the church buildings.
Recommendations
- Vacuum clean church and hall regularly.
- Block potential entry points around doors and windows, as well as checking potential entry points via damaged ceilings.
- Use a Mortein type contact insecticide around the perimeter of the buildings, external windows and sills, and around the entry doors, but not internally.
- Seek permission to remove excess Elm saplings along Perthville road between church and the entrance to Perthville village without destroying the ambience of the road side vista.
- Seek help from BRC to inject targeted pesticide into large adult trees along the roadside.
Notes supplied by David Goldney on 31/01/2017, sourced and modified from various reliable Web sites. David is a member of BCCAN and Greening Bathurst. Neither organisation necessarily endorses the views that I have expressed.