Population dynamics of stubby root nematodes (Trichodorus and Paratrichodorus spp.) associated with ‘Docking disorder’ of sugar beet (Beta vulgaris L.), in field rotations with cover crops in East England

Stubby root nematodes (SRN)—(Trichodorus and Paratrichodorus spp.) are economically important plant parasitic nematodes (PPNs) in east England and have been reported to cause up to 50% root yield reduction in sugar beet (Beta vulgaris). The banning of nematicides such as Vydate (oxamyl) due to environmental concerns limits the management options available to farmers for the management of this nematode. Cover crops (CCs) present a practical option for farmers to manage nematodes whilst enhancing other soil properties such as structure, organic matter content and soil biodiversity, which contributes to the overall soil health. This study evaluated the population dynamics of SRN in field rotations with cover crops. The effect of cover cropping on the yield and quality of follow-up crop, sugar beet, was also evaluated. Field experiments were initiated at two sites in England: Bury St Edmunds, Suffolk (site 1) and Docking, Norfolk (site 2). The cover crops evaluated were—Indian mustard (Brassica juncea), oilseed radish (Raphanus sativus), daikon radish (Raphanus sativus var. longipinnatus), Festuca-lolium hybrid grass (Festulolium loliaceum) with endophyte (E+) and without (E−), Italian rye grass (Lolium multiflorum), phacelia (Phacelia tanacetifolia) and opium poppy (Papaver somniferum). At site 1, plots drilled with brassica cover crops, Indian mustard and oilseed radish, had significantly lower SRN reproduction factor (Rf) (p < .05) compared to the fallow control and daikon radish. In site 2, plots drilled with the cover crops—Italian rye grass, Indian mustard, grass without endophyte (E−) or left fallow and undisturbed had a significantly higher Rf (p < .05) compared to plots with phacelia, opium poppy, and disturbed or sterile fallows. Sugar beet root fanging (%) and root soil tare (%) were lower in plots that had lower SRN reproduction, that is, phacelia, opium poppy, sterile fallow, and disturbed fallow. Environmental variables such as rainfall and soil temperature also influenced SRN densities at different sampling points where SRN increased with increasing rain and decreasing soil temperatures. Results from this study indicate that under field conditions the population dynamics of SRN are influenced by multiple factors such as the host status of the CCs grown, weed occurence which serve as alternative hosts as SRN are polyphagous in nature, soil temperature, rainfall, and soil disturbance. It was also clear that multiplication rate of SRN in CCs such as phacelia and opium poppy was lower despite SRN being able to multiply in all cover crops tested in this study.