The effect of soil‐applied granular pesticides and irrigation on the yield of sugar beet in fields infested with Trichodorus viruliferus

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Abstract
SUMMARY: In field samples taken on a grid pattern during four winters over an 80 ha farm there were many Trichodorus viruliferus (up to 3000/litre soil) in light soils but few in heavier soils. Depth samples taken during the summer showed Trichodorus to be the only nematode genus which was more numerous below plough depth than in the plough layer. In field experiments in the most heavily infested part of the farm, soil‐applied granular pesticides did not increase sugar yields following the dry spring of 1982; aldicarb increased sugar yields in one experiment following the wet spring of 1983 although it, and other granular pesticides, did not affect yield in an adjacent experiment where T. viruliferus were fewer. Irrigation during the dry summer of 1983 maintained relatively large populations of T. viruliferus, whereas in unirrigated plots without aldicarb populations declined by over 50%. Economic thresholds for T. viruliferus in 1983 at Broom's Barn were about 700/litre in unirrigated soil and 300/litre in irrigated soil.