Effects of environmental change: increased nematode pest status on UK crops.

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Plant parasitic nematodes are important, economic, agricultural pests. They cause crop damage both directly as a result of their feeding and as viral vectors of diseases such as spraing on potatoes. Plant parasitic nematodes can be classified as either sedentary e.g. potato and beet cyst nematodes and root knot nematodes, or free-living e.g. stubby root and needle nematodes. Nematicides have historically been used to control nematode problems but have tended to be broad spectrum and relatively persistent. Legislation has already resulted in the recent loss of two major nematicides in response to the environmental concerns that their use raised. Amendments to relevant EU directives will cause loss from the market of the three remaining nematicides with limited prospects for safe alternatives becoming available. The loss of nematicide control and potential changes in climate present a dire situation for many British growers.Climate change is predicted to increase summer temperatures in the UK by 2.4-4 oC and alter rainfall patterns with summers predicted to be drier by 30% (a median value from several climate models). Climate change could result in increased economic damage caused by nematodes that are already prevalent in the UK. Higher soil temperatures will increase the rate of development of plant parasitic nematodes resulting in greater multiplication of some and hence more damage to host crops. Earlier maturity of potato cyst nematodes may influence the proportion of the second generation that enters a period of dormancy, allowing greater re-infection of the crop within a growing season. The number of generations of beet cyst nematodes may also increase. The impact of cyst nematodes is enhanced when crops must also withstand the abiotic stress of dry soils as reported for potato, beet and other crops. Climate change may cause nematode species that are prevalent, but infrequently damaging in the UK, to become important agronomic pests. Dry soils are detrimental to control of cereal cyst nematodes. They are normally under natural control from fungi but this suppression is reduced in dry summers because some of their fungal enemies infect nematodes with zoospores that require high soil moisture levels for their activity. This risks damage to the next cereal crop from an increase in overwintering population levels of cereal cyst nematodes. Changes in rainfall will also impact on those free-living nematodes that attack plants. For instance, high soil moisture enhances the activity of trichodorids and longidorids close to the soil surface leading to seedling damage as in Docking disorder of sugar beet.Increased temperatures could lead to a greater threat from nematode species that are recorded rarely (but when found are present in high numbers) becoming widespread in the UK. There is a risk that alien species of root-knot nematodes, that are abundant elsewhere in Europe, can become established pests as UK soils warm. In this work, nematologists will collect the biological information necessary for a climate impacts modeller to integrate the new information with that already available to predict increased risks from nematode pests of UK agriculture as climate change continues. Simulation models of UK nematode populations will be developed and tested using primary data relating soil temperature and moisture to nematode development, multiplication rates and crop damage. The model will be refined and tested using secondary biological data prior to being used with the UKCP09 climate data to project the risk of future nematode occurrence. Resolution will be to 25km2 and be related to soil type. The insights gained will be used to develop pest management strategies to mitigate the impact of changes in nematode pest status. This is necessary given chemical control of nematodes as used widely in the past is unlikely to be available to growers following changes in EU legislation.