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Research updates

Read the latest Potato Update reports from FAR:


Ongoing Research Investment Streams

Psyllid / Candidatus liberibacter solanacearum (CLso) research

The main research programme has been two MPI SFF projects, the second of these (11/058) projects finished in October 2014.

The focus of this research has been on developing insect management programmes which use a combination of forecasting, monitoring and targeted insecticides.

The research to date has shown a good ability to use degree days to predict psyllid epidemics in the Pukekohe region and forecast insecticide intervention and there has been a significant amount of research conducted on a range of spray approaches and developing robust insecticide spray programmes.

The research has also shown sticky traps can be used as an indicator of adults moving into the crop in the Pukekohe region. Positioning sticky traps in the headlands and within the crop could be used to indicate if a headland spray will be adequate to control the pest.

The MPI SFF 11/058 programme also links to other government funded research that has been undertaken to better understand the disease life cycle, insect biology and life cycle and some molecular understanding of the pest.


Potato Yield research projects

Led by Plant and Food Research (PFR), the focus was to identify the factors responsible for reducing yields in potatoes.

The first year results included some modelling work to identify yield potential at each site linked to a survey of process potato crops in Canterbury. This showed that the yield gap was often over 30t/ha with top yields being 66t/ha. It was found that nutrients were generally not limiting and that foliar diseases were well controlled. The research to date has indicated that soil constraints and particularly soil borne diseases are reducing yields.

The results indicated that the major soil borne disease was Rhizoctonia (both AG2.1 stem canker and AG 3 tuber canker were present) and although new ground (potatoes only once in 10 years) had less disease there was not a marked difference in yield between new and old ground. The crops in rotation do appear to be influencing Rhizoctonia with less disease following grass than following wheat.

Spongospora (powder scab) root galling was also common. Nematodes (potato cyst nematode PCN (Globdera) and root knot (Meloidgyne) and root lesion nematode (Pratylenchus)) were reported in crops but the impact on yield is not clear.


Potato Research Projects

Ongoing TPP research includes:

Regional Pest Management Strategies

Psyllid work with continue with trials established in Matamata, Manawatu and Canterbury. The incidence, importance and timing of pests varies markedly between potato growing regions in New Zealand. The aim of the three field trials is to develop regionally focused pest management strategies, initially focussing on tomato potato psyllid (TPP) and zebra chip disease, putatively caused by Candidatus Liberibacter solanacearum (CLso).
This project will focus on developing reduced insecticide management strategies by: using thresholds to commence a spray programme (psyllid-count based or Degree Days) and incorporation of agricultural oils into a spray programme to protect the crop from insect pests and consequently from being infected with CLso (TPP) or viruses (aphids).

Crop Covers

The Biological Husbandry Unit has undertaken some research on crop covers to exclude the insect pest and have had extremely good results at controlling TPP. The covers also significantly reduced the incidence of late blight so could markedly reduce pesticide application in potatoes. To date the commercial evaluation of the covers and comparison of these to other control methods (forecast and spray or calendar spray) have not been made so the cost benefits cannot be determined. While these covers may not be an option for process potatoes they may have a fit for early generation seed potatoes (they could also exclude aphids and reduce virus risk). Internationally these covers are widely used on brassica crops.

For more information on crop covers in the integrated insect management research project.

Evaluation of Oil Sprays

Research by Peracto has evaluated oil sprays and the use of oils alternated with insecticides and comparisons of different insecticides. The oils, particularly at the higher rate on their own or in conjunction with insecticides, appear to give good levels of control when under low insect pressure.

For more information on evaluation of oil sprays in the integrated insect management research project.

Review of Agrichemical Options

Agrichemical companies have evaluated a number of products in trials.


Evaluation of Tamarixia as a biological control (natural parasitoid of psyllid in Mexico and US) for psyllid in New Zealand. Tamaraxia will not give control in the paddock situation as it only attacks fourth instar larvae but it may suppress overall background population.

For more information on the use of Tamarixia in the integrated insect management research project.

Growers report yield has been decreasing each year.  In other crops growers have the ability to utilise the genetic gain from breeding but in potatoes, as there is very little change in cultivars, any yield improvement has to come mostly from agronomics.

Soil Quality – Compaction

Compaction has been identified as being a problem and a value of 1.5 MPa has been identified as a critical factor above which yield is reduced. Although it was identified that compaction reduced yield the research has not identified what aspects of crop management are causing compaction or if yield loss is directly due to compaction or to the impact of compaction on plant water use or irrigation management.

FAR were successful with an application to MPI SFF. The project will run for three years (from 2015) in Pukekohe, Manawatu and Canterbury and focus on ‘Increasing potato yield through understanding the impact of crop rotations and soil compaction’.

Year 1 is well underway with eighteen commercial potato field crops being evaluated for this season. The desired outcome of the project is to better understand where potatoes fit in the rotation, how to reduce soil compaction and improve soil structure whilst understanding how all these factors impact of soil borne diseases. Comprehensively testing abiotic and biotic factors along with understanding the rotation and soil borne diseases over three years will give us the full spectrum of how and where potatoes fit best along with understanding where we can increase yield.

In-Paddock Variability.

The yield gap project has identified large in-paddock variability with up to 90t/ha in some parts of some paddocks.

The use of guidance technology and variable-rate application, based on soil testing is being undertaken, but there is limited crop-based management of inputs. There may be opportunity to manipulate some inputs. In-paddock variability can be relatively easily identified using remote sensing equipment (both NDVI and Infrared) but there are three major problems with potatoes:

  • Remote sensing can identify differences in a paddock but these need to be “ground-truthed” to determine the reason for any difference – e.g. canopy disease etc.
  • Often, by the time a difference is apparent on a crop sensor map, (even when it is ground-truthed), growers cannot implement a management decision that will change the crop performance.
  • Yield maps are generally used as the baseline reference for Precision Agriculture and this is both difficult and expensive to implement for potatoes.

Crop Rotations – Bio-fumigant Crops.

There is a significant amount of international data which outlines how different crops in a potato rotation influence the incidence of a range of pests, but only a limited amount of data on how these crops impact on yield. In New Zealand, and elsewhere in the world, there is interest in biofumigant crops, such as Caliente Mustard, with limited data on how they influence diseases and pests or crop performance. Thus it is not clear if, or when, growers should use these crops to maximise the value of a cropping program. The theory is that these crops produce gucosinolates that through enzyme action produce bioactive isothiocynates and these control the diseases.

There are two major programmes (internationally) looking at biofumigant crops in potatoes, in the US and UK. The UK programme only commenced in March 2014 and appears to be well-funded and long-term.

MBIE Psyllid Project

Realising potato export growth through sustainable management of the zebra chip disease complex

This programme addresses the major problem affecting the NZ potato industry, the recently arrived Tomato Potato Psyllid/Ca. Liberibacter solanacearum (TPP/Lso) complex, and is developing effective control measures and resistant potato cultivars for sustainable management of the TPP/Lso incursion.

Start date 01/10/2013, end date 30/09/2019, total contract value $6,665,400.00

The multidisciplinary team of Plant and Food Research scientists and international collaborators is studying the insect-pathogen interaction at levels ranging from the population to the molecular.

Key areas of research activity, are:

  1. Development of disruptant/attractant-based tools through understanding psyllid sensory cues;
  2. Providing better management information through understanding TPP population genetics and Lso association, as well as insecticide resistance status of TPP;
  3. Making progress toward developing resistant or tolerant potato cultivars using the information gained by understanding the potato plant’s responses to TPP and Lso in primary and secondary metabolism and in defence pathways; and
  4. Stakeholder communication to ensure technology transfer and uptake.

The outcomes of the programme will be achieved via several pathways involving growers, the processing industry, pest control companies and the joint Potatoes NZ Inc./Plant and Food Research breeding programme.

Benefits to the Maori economy will accrue through increased opportunities to participate in the growing potato industry and a return to production of Taewa (Maori potato), which has also been affected by the TPP/Lso complex.

Contact for further information – Gail Timmerman.