Abstract

Management of Heterodera schachtii, a major pest of sugar beet, has depended heavily on use of soil fumigants and nematicides. Objectives of this research were to assess more environmentally friendly management approaches: use of resistant cultivars, a seed treatment for early season suppression, and site-specific management of H. schachtii. Two H. schachtii-resistant cultivars, Nematop and HM1334, were evaluated for agronomic characteristics and resistance to diseases and H. schachtii. Nematop showed extreme susceptibility to beet curly top virus with associated low yield in field experiments. HM1334 had similar yields as susceptible commercial cultivars in most field tests. Experimental and commercial U.S. sugar beet cultivars were evaluated for reaction to H. schachtii in a growth chamber study. Differences in H. schachtii reproduction and thus susceptibility were observed in tested sugar beet cultivars. Resistant cultivars HM1334 and Nematop exhibited constantly low reproductive rates. Abamectin (STAN) seed coating at 0, 0.05, 0.1, 0.2, and 0.3 mg a.i./seed was evaluated for early-season suppression of H. schachtii under growth chamber and field conditions. Abamectin seed coating decreased H. schachtii populations in growth chamber tests. Phytotoxicity at higher rates was observed under growth chamber and field conditions. Six sugar beet production fields in Wyoming were assessed for spatial and temporal distribution patterns of H. schachtii. Four research areas were repeatedly grid sampled over a period of 4 to 5 years. Distributions were compared between years by paired t-tests. Two research sites were grid sampled in 2001 only and contour maps were created by use of the whole data set and two data subsets that each included only half of the grid points. One site was geostatistically analyzed by use of variogram modeling and kriging. Heterodera schachtii distributions were patchy within sugar beet production fields. Field populations from year to year changed over time in 6 out of 10 comparisons (P < 0.1). Grid soil sampling at 65 m grid spacing was sufficiently dense to see the distribution pattern at one site but not at the other. Geostatistical analysis indicated spatial dependence of H. schachtii density over a range of 95 m.