Influence of Nacobbus aberrans Densities on Growth of Sugarbeet and Kochia in Pots.

Among the physiological races of Nacobbus aberrans Thorne and Allen, only the "sugarbeet" race is present in the United States (5). This race reproduces on kochia (Kochia scoparia (L.) Schrad.), tomato (Lycopersicon esculentum Mill.), and sugarbeet (Beta vulgaris L.) but not on pepper (Capsicum annuum L.) and potato (Solanum tuberosum L. and S. tuberosum subsp, andigena Jus. and Buk.) (5). Kochia is an annual weed in cultivated and waste lands of the northern central and western United States. Suppression of sugarbeet plant weight ranged from 75 to 27%, compared with noninoculated controls, 30 and 60 days after single inoculations with 12 N. aberrans "subarbeet" race second-stage juveniles (J2)/cm 3 soil (6). Damage to pepper and tomato seedlings grown in soil infested with increasing densities (from 0.125 to 12 eggs/ cm 3 soil) of another race ofN. aberrans was reported in Mexico (8,9). However, little information exists on yield suppression of sugarbeet and other hosts caused by increasing densities ofN. aberrans. The "sugarbeet" race of N. aberrans may limit the growth of kochia and act as a biological antagonist of this weed in infested fields. Two greenhouse experiments were conducted to examine the relation between N. aberrans population densities and growth of sugarbeet and kochia in pots.