Potato IPM case study 3: IPM delivers Tomato Potato Psyllid control in New Zealand Potato Crops

In 2006 Tomato Potato Psyllid (TPP) (Bactericera cockerelli) was detected in New Zealand. This insect is a serious pest of potatoes and other solanaceous crops such as tomatoes, capsicums ,chillies,  eggplants and tamarillos. However, it can survive on a much wider range of host plants which means that once present in an area it is very difficult, if not impossible, to eradicate. It causes direct losses due to its feeding on plants but in processing (crisping) potato crops it is even more damaging because it vectors a bacterium, Candidatus Liberibacter solanacearum (Lso), that causes irregular colouring when the potatoes are fried.  This is commonly known as “Zebra chip”.

Prior to the arrival of TPP in New Zealand control of insect pests in most cases was achieved using insecticide applications but it was not a “heavy” spray program. McCain growers in the South Island were using an approach very similar to the IPM approach being implemented in Australia. Aphids and potato moth were the main pests to be dealt with and this was achievable without too many insecticide sprays.

Immediately after the arrival of TPP and the recognition of what this pest could do, things changed.  It became common for 14 or more insecticides to be applied per crop (some tank-mixed together and sprayed at the same time). The pest was not eradicated but damage was avoided or minimised.  It was generally accepted by the industry that this was not desirable or sustainable but was the only approach that could be relied on at that time to prevent serious losses due to TPP and Lso.

There was an intense research effort put in place with many researchers searching for more knowledge and better control options. One of these efforts was Project PT09004, which was a collaboration between IPM Technologies P/L (an Australian company specialising in IPM) and The New Zealand Institute for Plant & Food Research (Plant & Food NZ). This project aimed to find control measures for TPP that would be compatible with an IPM approach, both in NZ at first and then in Australia, when and if it arrived.

The first step of this project involved testing in New Zealand of potential insect predators nominated by IPM Technologies. This work was carried out in Auckland and demonstrated that at least four key generalist predators that are of importance in Australian potato crops would prey on all life stages of TPP. Knowing this, Dr Paul Horne and Jessica Page from IPM Technologies visited a range of locations and crops to attempt to develop an IPM approach to dealing with the pest. They looked at possible cultural controls and how to best use selective insecticides that were not going to disrupt the key beneficial species. They also looked at how best to use insecticides (timing and placement).

At the start of the third (final) year of the project they had formulated a draft strategy but they needed commercial crops in which to test it. Fortunately, with the support of independent agronomist Duncan McLeod they gained the co-operation of Canterbury farmers Danny Lovett and Ross Hewson who each agreed to follow the proposed strategy on one paddock. The paddocks were monitored intensively by entomologists from Plant & Food NZ.

The potatoes from the two paddocks were destined for processing by McCain, and they were processed successfully without damage. Following this success McCain growers in New Zealand all largely followed the same approach in subsequent years (2013 – 2014). The approach involved a greatly reduced use of insecticides but also involved using very different types of insecticides (no broad-spectrum insecticides products).

Since 2013 there have been changes in the range of insecticides available and also in the level of TPP in the wider environment across New Zealand. Trapping for adult TPP is used to indicate the pest pressure from outside of the crops and monitoring in the crops indicates the life stages present and so allows the selection of appropriate insecticides. Duncan McLeod comments that “TPP is manageable without using frequent applications of broad-spectrum insecticides. However, dealing with this pest involves understanding its biology and also the different requirements for different sectors, that is processing, seed or fresh market”.

New Zealand potato growers that are implementing IPM are able to achieve the same level of TPP (and Zebra Chip) control as growers that are instead relying on a heavy spray program that includes broad-spectrum products. The advantage for the IPM growers is that by using only soft selective products, they can preserve an army of natural predators that work day and night to stop TPP from establishing in their crops. By minimising the number of insecticide applications and using border sprays rather than treating whole crops where possible, IPM growers save on labour and chemical inputs and this helps to balance out the fact that the soft insecticides are more expensive than the ‘cheap and nasty’ broad-spectrum products.

Can we expect to be able to manage TPP successfully within an IPM strategy in Australia? The combination of the development of an effective IPM strategy that is proven in New Zealand; a handful of new soft insecticide options; and the fact that there are many more potential insect predators of TPP in Australia than in New Zealand means that there is good reason for Australian potato growers to be optimistic about controlling this pest using an IPM approach.