Effect of crop rotations with green manures and other crops; fallowing; continuous potato cultivation; soli application of PCNB and chlorocin-their doses and time of application on the build up of common scab caused by S. scabies was studied at the Central Potato Research Station, Modipuram in a common scab infested field of known disease intensity. In plots where potato crop was grown continuously for two years disease intensity increased by 35.5% (1st year) and 65.5% (2nd year). PCNB @ 40 kg/ha a.i. applied as soil treatment brought down the disease level by 52.2% in the same year but it's residual effect was limited (18.8%). Subsequent application in the next crop season did not prove much effective (11.1%). Chlorocin was found ineffective. Amongst rotations, potato-wheat-rice-potato and potato-clover-bajra-potato proved superior over other rotations and fallowing. Slight depression in yield was observed in PCNB applied plots but was statistically non-significant.
