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In experiments in 1979 and 1980 in eastern England, the spread of eriophyid mites and ryegrass mosaic virus (RMV) from transplanted old sward through plots of newly sewn Italian ryegrass greatly exceeded spread by windborne mites from outside the plots. During the summer and autumn of each year, mites and RMV spread at least one metre through the ryegrass (6/7 rows) from the old sward. Applying aldicarb (10 kg/ha equivalent) to the seedbed before sowing the Italian ryegrass prevented colonisation by mites and greatly decreased spread of RMV from old sward. lt is concluded that old diseased swards should be completely killed before reseeding and that RMV is likely to spread quickly to plants slot-seeded into old pastures. The use of acaricides might prevent this spread but would be costly. [ABSTRACT FROM AUTHOR]