Mapping Infestations of Potato Cyst Nematodes and the Potential for Spatially Varying Application of Nematicides

The most important constraint to potato production in the UK is the damage caused by the potato cyst nematodes (PCN) Globodera pallida and Globodera rostochiensis. These are serious pests, capable of causing substantial yield loss. Modern management systems depend heavily on nematicides which, at c. £360 ha−1 for granular and c. £550 ha−1 for fumigant nematicides, are costly to use. Mapping field infestations of PCN gives growers the option of applying nematicide variably across their fields. We intensively sampled a field, infested with G. pallida, before and after potatoes were grown and used the results to consider decisions the grower might have taken and to examine the consequences of various actions. Sampling intensity is important in generating accurate maps. In our results, spatial independence in PCN counts occurred at about 60 m, although there was also evidence of spatial independence at a range of 10–20 m in intensively sampled areas of the field. A strategic requirement to keep PCN population densities small, rather than the more tactical objective of avoiding yield loss, would mean blanket treatment of infested fields with granular nematicide. Maps could then be used to target ‘hot spots’ of PCN infestation for additional treatment with fumigant. This procedure would avoid blanket treatment with both types of nematicide, thereby diminishing the cost of chemicals applied and reducing possible environmental damage. However, the inverse relationship between pre-planting population density and multiplication rate of PCN makes it difficult to devise safe spatial application procedures, especially when the pre-planting population density is just less than the detection threshold.