Pest control for primary industries

Cassida beetles introduced to Southland have been successful in eradicating the Californian Thistle. This pest is a burden to farmers with an industry cost of about $200 million dollars annually.

Pest control represents a significant ongoing cost for most farmers but recent scientific advances promise better outcomes.

Chemical control agents have come a long way, with much more selectivity now possible. An example is new selective herbicide `Puma S' for use against yellow bristle grass (YBG).
YBG is a significant weed of pasture and crops, especially prevalent in the Waikato. It reduces feed production by up to 20 per cent, with costs for replacement feed or pasture renovation estimated by DairyNZ at $500/ha.

As an alternative to more traditional chemical controls, the development of appropriate biological control agents for key agricultural pests is becoming more common. Put simply, a biological control agent is when one organism is used to control another. Once established, pest control of the target organism continues as long as the population of the control agent is maintained. Such control is extremely selective.

Control of the clover root weevil is an excellent example. Introduced accidentally in the 1990s, it devastated our clover pastures in many regions. In order to control the clover root weevil, a tiny parasitic wasp from Ireland was introduced and is making a significant contribution to the control of this pasture pest.

Another example is the use of cassida beetles against Californian thistle. Thistle control is a burden for farmers, with chemicals, mechanical topping and lost production estimated to cost close to $200 million annually. Control is particularly difficult for hill country farmers, where topography may make expensive helicopter spraying the only viable option.

Five years ago, scientists introduced cassida beetles on to farms in Southland. These have proved so successful that Agresearch and farmers have submitted a proposal to the Sustainable Farming Fund to investigate its release into hill country areas of North Canterbury and the North Island. The beetle eats only thistles and when numerous can defoliate plants.

Another Sustainable Farming Fund project in Manawatu-Wanganui is investigating options for biocontrol of field horsetail. A fern-like plant native to North America and Eurasia, it has become a serious invasive pest in wetter regions of New Zealand. Traditional control measures are costly and largely ineffective. At present, no selective herbicide is available. Field horsetail has an extensive root system, which enables it to regrow aggressively every year. It can be toxic to livestock, while making hay and silage supplements go rank.

Federated Farmers is very supportive of efforts put into the development of bio-control agents. Working with natural processes often delivers a good long-term outcome. A combined approach of traditional chemical solutions, clever on-farm management and use of bio-control agents needs to be co-ordinated to maximise efficient and cost-effective pest control in our agricultural sector.