Systemic application of sodium silicate can significantly enhance the levels of leaf silica in winter wheat (Triticum aestivum L. cv. Mercia), suggesting that this material could reduce the palatability of plants to vertebrate herbivores (e.g. rabbits, Oryctolagus cuniculus L.). A bioassay was developed using hydroponically grown wheat plants. Plants treated with sodium silicate were significantly more resistant to grazing by wild rabbits than untreated plants, with severe, potentially lethal feeding damage being reduced by over 50%. Further studies were carried out to develop more practical techniques for boosting silica levels in plants using silicon-rich ‘fertilisers’ including calcium silicate and calcium silicate slag (CSS). Silica levels were elevated in the plant 1.9–2.8 times over the control through the application of various silicon materials, in line with those of the hydroponic treatment. Encouragingly, levels of silica were elevated even in young wheat plants, which are most vulnerable to rabbit damage, and in a range of wheat varieties. The use of CSS is particularly promising because of its lower cost in comparison with calcium silicate, and it has a proven track record in slag fertilisation of rice and sugar cane crops. At the optimum CSS application rate of 3 g silicon L−1 soil, wheat silica levels were approximately doubled, with no detrimental impacts on long-term growth or yield. Crown copyright 2006. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.