ROGUING POTATO CROPS FOR VIRUS DISEASES

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Abstract
Removing virus‐infected plants from plots of Majestic potatoes at Rothamsted on 2 July 1947 did not reduce the spread of leaf roll but reduced rugose mosaic (potato virus Y) to about one‐fifth of that in plots rogued on 21 July or left unrogued. Roguing Arran Pilot potatoes on 16 June or 2 July reduced leaf roll to five‐sixths of that in unrogued plots; roguing on 16 June reduced rugose mosaic to about half that in plots rogued on 2 July, and about a quarter of that in unrogued plots. Lifting Arran Pilot potatoes in mid‐August reduced virus diseases to about two‐thirds.Roguing flattened the gradient (decrease in percentage plants diseased with increasing distance from the source of infection) with rugose mosaic, but had little effect with leaf roll. Evidently any plants prevented by roguing from contracting virus Y were near the initially infected plants.In 1948, Majestic and King Edward potatoes at three places were rogued during 22–24 June and tubers were dug during 28–30 July and again at the end of the season. Leaf roll spread more in Majestic than in King Edward, and rugose mosaic spread more in King Edward. Roguing reduced the spread of both by about one‐fifth at Rothamsted, but had no effect at Sutton Bonington. At Bretton, in the Derbyshire hills, roguing had no effect on leaf roll, but prevented the spread of rugose mosaic.The small benefit occasionally achieved by roguing in the ware‐growing districts of England does not make the practice economically worth while.