Plant parasitic nematodes are microscopic worms in soil that feed on plant roots, stunt their growth and make root systems much less efficient at withdrawing nutrients and water from soil. The yields of nematode-infected crop plants are reduced and annual losses world wide are estimated to cost US$100b, despite control measures. In the UK the major nematode pest, potato cyst nematodes, causes £50m of yield losses each year to the potato crop. Nematodes usually do not cause characteristic symptoms in plants and the general stunting of infected crops is often attributed to other causes; nematodes are frequently referred to as the hidden enemy. In intensive cropping systems growers depend on host resistance and chemicals (nematicides) to manage nematode pests. Nematicides are some of the most toxic products used in crop protection and their use has been banned in several European countries because of environmental concerns and public pressures to reduce dependence on agro-chemicals. There is an urgent need to develop other control methods to replace current nematicides. This research proposal builds on recent work at Rothamsted Research that has demonstrated that root-knot nematodes, which include the most important nematode pests in world agriculture, may use indole acetic acid and other plant-derived indole compounds to locate and invade host-plant roots in soil. We will confirm this observation and identify the most active compounds. We will also investigate how these compounds cause changes in nematode behaviour and guide them to infection sites. The output of this project will provide nematode targets for chemical or genetic intervention. Interfering with host recognition processes, offers great promise for the design of efficient, specific, safe and environmentally friendly management tactics to limit plant damage due to major groups of nematode pests, including the potato cyst nematodes.