EN
Susceptibility of different sugar beet cultivars to larva damage caused by the third generation of beet fly (Pegomya hyoscyami Panz.) was tested in the field condition in 2008 and 2009. The effect of the pest damage on yield was estimated. Twenty four cultivars were tested in one location in 2008 (Piołunowo). Ten cultivars were tested in four locations in 2009 (Tytlewo, Tylice, Piołunowo, Zbójno). Experiments were designed by randomized blocks in four replications. Estimation of damage was done in the end of September using a six degree scale where: 1 – means very slight damage, 5 – heavy damage. The level of infection was calculated as a percentage. Yield was estimated on each plot by digging beets from 10 m2 area. Analysis of variance and correlation was done at p < 0.05. Significant differences in susceptibility of sugar beet cultivars to damage cause by beet fly larvae were stated. The level of damage ranged from 10% (cultivar Balladyna) to 45% (cultivar Picasso) in 2008. Six cultivars was weakly damaged, sixteen moderately, and two strongly. No significant correlation between leaf damage and root yield (r = 0.194, N = 24, p = 0.928). The average damage level was from 12% (cultivar Nancy) to 36.6% (Aldona) for four experiments in 2009. Damage level was week for two cultivars, moderate for six, and strong for two. Lack of correlation between root yield and damage level was stated. The obtained results revealed that sugar beet protection against the third generation of P. hyoscyami is pointless in case of a low or moderate level of damage.