The effects of yellowing viruses on yield of sugar beet in field trials, 1985 and 1987

The separate effects of beet yellows virus (BYV) and beet mild yellowing virus (BMYV) on yield of sugar-beet cultivars inoculated at different growth stages were assessed in field trials in 1985 and 1987. Early or mid-season inoculation decreased sugar yield by up to 47% for BYV, and up to 29% for BMYV. Infections after the end of July had no significant effect on yield. Both viruses caused significant increases in the juice impurities sodium, potassium and amino-nitrogen after infecting plants early in the season. Yield losses associated with infection were determined by the causative virus, the time of infection, and susceptibility of the sugar-beet cultivars.