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New on-line PCN model launched

8 April 2013

 

AHDB Potatoes has recently launched a new on-line model for Potato Cyst Nematode (PCN), replacing an older CD version. The new pallida model is more user friendly allowing more flexibility to look at “what if” scenarios. 

 
PCN is the most significant pest of potatoes in Britain, with an estimated 64% of potato land infested, with Globodera pallida being the dominant species. Estimated crop loss due to infestation is nearly £26M* a year, with some losses not attributed to PCN due to low levels of infestation being difficult to detect.
 
“When land becomes infected, it can take many potato crops within the rotation before the level of PCN is high enough to be detected. Also with the distribution across a field, sampling can be hit or miss as to whether it is found with early infestations,” says Gary Collins, AHDB Potatoes’s PCN specialist. 
 
“Although there are infestations of G. rostochiensis, the biggest issue is with G. pallida. This is due to a number of reasons. Varieties are at best, only partially resistant to pallida, although there are new varieties coming to the market with higher resistance scores than we have seen in the past. Also pallida has a longer hatching period, this means that some later hatching will occur when any nematicide used may have degraded below the threshold for control”.
 
It may appear that a low level of 1 egg per gram of soil can be ignored in order to reduce the cost of production, but if a variety that has no tolerance or resistance is being grown, such as Maris Piper (25% of the potato area in GB) this is the best time to tackle PCN. 
 
At low levels there is the largest increase in population, which can be seen in the graph below. Population increases can be measured using the Pf:Pi ratio, which is the ratio between the final and initial populations. 
 
In the example below, Maris Piper grown in a sandy loam soil with an initial population of 1 egg per gram will increase the population from 1 to 28.5, giving a Pf:Pi ratio of 28.5. 
 
When the initial population is 49, the Pf:Pi ratio is 3.6. The legacy of not managing a low population at planting is elevated levels of PCN for the next potato crop (9.3 eggs per gram of soil in the example).
 
 
 
The model will also show the theoretical yield. Using the same example above where an estimated maximum Maris Piper yield of 50t/ha was used, the model shows the yield reduction due to pallida infestation. 
 
As there are many factors than can decrease yield over the growing season, it is difficult to attribute all or part of this loss to PCN when the initial population is low. The benefit of the model is to highlight the effect of low initial populations on yield. The example below shows a 3 t/ha reduction from the estimated maximum yield of 50t/ha in the first cropping year. So the use of a nematicide will not only help to control the PCN population as part of an integrated approach, but will help protect yield and could pay for itself even at low initial populations.
 
 
“The plan is to add G. rostochiensis into the model and to add connectivity to the British Variety database for a complete list of resistance scores,” adds Gary, who would be interested in feedback about the model’s functionality and the proposed future developments (email: gary.collins@ahdb.org.uk).
 
 Industry responses on the old model suggested a better user interface and useful notes to describe key attributes of PCN control. These have both been incorporated into the new model. 
 
Gary concluded “The newly formed Nematode Management Initiative, a group that includes Agchem manufacturers and nematode experts, will provide additional information when it becomes available. This will include guidance in areas such as sampling strategy and a best practice guide to incorporation. I would encourage you to open the model and look at various scenario’s that will help to show suppression of your G. pallida populations”.
 
The model can be found in the toolbox on the AHDB Potatoes’s website at www.potato.org.uk/online-toolbox/pcn-calculator
 
*Pesticide availability for potatoes following revision of Directive 91/414/EEC: Impact assessments and identification of research priorities.
S Twining, J Clarke, S Cook, S Ellis, P Gladders, F Ritchie & S Wynn, ADAS
May 2009
 
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