Pest Alert for Lilly Pilly Hedges

This is a repeat of an article written on the Coffs Harbour Garden Club’s blog some time ago. It has always generated a lot of comment and interest. The latest advice is for a Yates product – Baythroid. You can see product reviews here where some claim success. What has to be taken into account is that this product is HARMFUL to bees so if there are any present avoid using Baythroid. Read instructions and warnings thoroughly before use.

 

Looks a pretty ‘cool’ beetle with its glossy pale green colour? Well think again folks, this little critter can completely decimate your Lilly Pilly (Syzygium) hedge. If your hedge is looking a bit like the following image ……. read on for the bad news.

For some time the green strip leaf beetle Calomela pallida was thought to be the culprit for the edges of Syzygium leaves being chewed which gave the hedge a sparse, lacy appearance. However, Dr Chris Reid, an Entomologist and Leaf Beetle expert at the Australian Museum in Sydney correctly identified Paropsides calypso was to blame.

This 9mm, bright green beetle is an Australian native beetle from northern NSW but can now be found from the tip of Queensland all the way into Victoria – mainly due to the popularity of Lilly Pilly hedges and poor quarantine between nurseries. It has taken from 5-10 years for the beetle to spread such a huge distance.

Its eggs are laid on leaves or leaf buds, and the green larvae are relatively solitary (not clustering) during feeding. Paropsides calypso pupates in the soil and both beetles and larvae feed on Syzygium leaves. The larvae is quite large – around 2cm, pale green, glossy and a bit like a curl grub stretched out (quite chubby). 

As this pest has only recently been identified as being a huge problem, there is not a lot of information on just how best to be rid of it. If you are lucky enough to have chooks a sweep along the hedge might knock the larvae to the ground and the ‘girls’ can forage for the juicy larvae, also as they pupate in the ground the chooks might be able to scratch them out too. Neem oil has been found to be effective but one has to be quite diligent to get good spray coverage on the hedge. There was a post written earlier this year about Diatomaceous Earth – this might be worth a go too.

Growing plants as a monoculture can be a problem as it has been found that one by one the world’s most toughest garden plants are succumbing to newly-discovered, debilitating pests and diseases – take for instance the Elm, Ash, Buxus, Roses, Agapanthus, Impatiens, Clivea etc etc – the list goes on.

Every time we plant a hedge, or a single-species border or a sweep of identical perennials, we can spread and encourage either existing or future pestilence. Just figure, the pathogens that are attacking these mass-planting favourites aren’t usually unknown (as is the case with Paropsides calypso) however when we start to supply them with unlimited food all conveniently co-located, they can rage out of control. With so much food on hand they can quickly multiply and spread rapidly, the plant species affected doesn’t have time (through seed-grown generational development) to generate resistance.

Monoculture planting is not a modern design element in gardens – Boxwood (buxus) hedges, for instance have been used for hundreds of years in formal gardens. Its use has been popular because it can be shaped to produce intricate topiary and have a dramatic effect in very formal arrangements like knot gardens. Design elements with grouped swathes or hedges of single plants to provide harmony and unity within a garden space have always held sway in garden design.

Why do we grow hedges? Is it for privacy, as a boundary marker, to keep intruders out, as a windbreak, as a way of creating special spaces within a garden, or as a feature? …….. most hedges would be grown for more than one of these purposes.

Perhaps a sure fire way of preventing the spread of these modern day pests is to have diversity in our plant selections in our gardens. If privacy is the main driver for a hedge and space allows, an informal, or natural hedge could be worth a thought. The disadvantage of course, is that there is not the actual ‘formality’ of a hedge. On the flip side though, a natural hedge of mixed plantings will only require light pruning from time to time and provide a wonderful soft backdrop in your garden. Of course, the excellent added bonus would be encouraging a diverse cross section of fauna to your garden to assist with management of pests!


Further reading can be seen at Derek J. Whitten’s blog

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