Rabbits cause an estimated $225 million in damage to crops each year in Britain.

Researcher David Cowen and colleagues at Britain's Central Science Laboratory near York say the application of slag to wheat growing in greenhouses has no effect on yield but causes the plants to incorporate the silica and express it as spiky structures on their leaves. The spikes deter rabbits by abrading their teeth and causing stomachaches.

Since humans only eat the wheat grain, the repellent would only affect the rabbits. When the slag-treated plants were compared with normal plants, grazing damage fell by more than half.

Slag -- or calcium silicate -- is a plentiful byproduct of blast furnaces and is inexpensive and environmentally friendly. It has been identified as an effective fertilizer in rice paddies and sugar cane fields.

The research appears in Chemistry & Industry magazine.

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