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Broom

Five different agents have been released in Southland to target broom (Cytisus scoparius). In addition, the broom twig miner moth (Leucoptera spartifoliella) has spread to Southland from other parts of New Zealand. Each agent affects different parts of broom plants at different times of the year. When all broom agents are present at the same time they place constant pressure on broom populations and reduce the impact of the affected broom plants.

Broom psyllid (Arytainilla spartiophila)

Broom psyllids were first released in Southland in 1995. Since then this tiny insect has spread to broom throughout the north-west part of the region. Both adults and juveniles feed on sappy new growth causing broom plants to wilt. In areas where the density of psyllids is high, the damage to broom plants can be severe and may kill broom seedlings.

The number of psyllids available to harvest each spring is usually high. Field days are held at this time so members of the public can collect psyllids to release on their property. Please contact Environment Southland to find out about the next broom psyllid field day.

Broom seed beetle (Bruchidius villosus)

Broom seed beetles were first released in Southland in 1995 but they have been slow to spread out on their own. The impact caused by this agent on broom is not obvious, as it is the beetle larvae which cause the damage by feeding on broom seeds. This slows down the rate at which populations of broom spread. While broom seed beetles are not numerous in Southland, they are plentiful in other parts of the South Island. This summer (2010) we will harvest beetles from other areas to carry out more releases in Southland.

Broom leaf beetle (Gonioctena olivacea)

This beetle is one of the more recent biocontrol agents which target broom. It was first released in Southland in 2007. Both the adult beetles and larvae feed on broom, damaging the leaves, growing tips and fleshy green stems. Heavy feeding damage reduces the plants' ability to photosynthesize and growth is checked. It is too soon to tell how much damage this agent will cause to broom in Southland. We will continue to monitor release sites to help determine what impact this biocontrol agent is having.

Broom shoot moth (Agonopterix assimilella)

This new biocontrol agent was first released in Southland in 2009. The caterpillars of this moth damage the broom by feeding on soft new growth and can sometimes kill whole stems and branches by ring-barking them. It is hoped this agent will perform well in New Zealand as it can tolerate a variety of climates and should affect broom wherever it grows. Highly mobile insects such as moths can make excellent biocontrol agents as they are able to disperse widely and establish new populations where they encounter their host plant. It is too early to tell how well the broom shoot moth will establish and spread throughout Southland. We will continue to monitor existing release sites to help determine whether we need to actively distribute this biocontrol agent, or can let it disperse naturally.

Broom gall mite (Aceria genistae)

This broom biocontrol agent was first released in Southland in 2009. These tiny mites damage broom by feeding inside the buds of stems. This activity causes the broom to produce galls which stunts the development of the plant. Over time successive gall formation can severely reduce the growth of broom plants and hinder flowering and may even kill whole bushes. It is too soon to tell how much damage this agent will cause to broom in Southland. We will continue to monitor release sites to help determine what impact the broom gall mite is having.