Current: Development of crop management strategies for ‘free-living’ plant parasitic nematodes infecting sugar beet (Beta vulgaris)

Timescale: 2020 - 2023
Project Lead: Nyambura Mwangi - PhD study (Supervisors: Dr Matt Back, Prof Mark Stevens & Dr Alistair Wright)
Project Sponsor: Harper Adams University and BBRO

Project Summary

Plant parasitic nematodes (PPNs) are important pests for many crops globally and result in a c. 14% loss of production annually, which equates £132 billion. The sugar beet crop is no exception, being subject to infection by a variety of different PPN species, including those categorised as free-living. Free-living PPN’s are ectoparasitic, meaning that the nematodes feed from the surface of roots and complete their life cycle within the soil. In the UK, stubby root (Trichodorus and Paratrichodorus spp.) and needle nematodes (Longidorus spp.) are the most economically important genera of free-living PPN.

Main Objectives

They are generally restricted to sandy (light) soils of higher pH and low organic matter. However, some species of Longidorus occur in heavier soils with higher clay and organic matter content. Nematode activity and subsequent damage occurs when the soil conditions are moist during seedling establishment. Stubby root nematodes feed just behind the root cap of tap roots producing brown necrotic lesions, fanging and yield loss of up to 50%. The symptoms of stubby root nematode damage is known as ‘Docking’ disorder, after the English village where the disease was extensively studied in the 1970s.  Meanwhile, feeding by Longidorus spp. can cause diffuse patches of plants of uneven size, sometimes with nitrogen and manganese deficiency. Swellings or galls may occur at the root tips and this is often accompanied by local necrosis around the point where feeding took place.

Management options for stubby root and needle nematodes are extremely limited in the UK. The oxime carbamate oxamyl (Vydate) is available to growers but most regard it as an expensive option for treating crops. For instance, 2,966 ha of sugar beet received nematicide treatment in 2016, equating to c. 2.82% of the total sugar beet grown. To compound matters, stubby root nematodes have a wide range of hosts, meaning that rotation planning is challenging, and additionally, there are no resistant cultivars for any of these nematode genera.

Currently, there is much speculation over the impact of cover cropping on free-living PPN species. A number of suppliers claim that their cultivars will reduce nematodes, but there is also some anecdotal feedback to suggest the contrary. It is possible that the confusion is due to generalisation and a lack of knowledge about specific nematode-plant interactions. However, there is little, if any, research conducted with UK sugar beet crops to support appropriate use of cover crops for this purpose. Cover crops may reduce nematode population densities through being poor hosts (trap crops), biofumigants (certain brassica species) or releasing toxic compounds from their roots (allelopathy). Such mechanisms of suppression requires thorough investigation.

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