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Title: Evaluation of a novel nematicide for use in the management of the potato cyst nematode, Globodera pallida
Author: Norshie, Patrick M.
ISNI:       0000 0004 7656 1429
Awarding Body: Harper Adams University
Current Institution: Harper Adams University
Date of Award: 2014
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The potato cyst nematodes (PCN) Globodera rostochiensis and Globodera pallida are two economically important potato pests constituting major limiting factors to production of the crop in the UK. Soil treatment with synthetic nematicides is wi dely practiced and is an essential part of an integrated management tactic for PCN. Howe ver, environmental concerns and human health issues have prompted the withdrawal o f a number of active substances leaving a limited few, which are not only under Euro pean Union review (Hillocks, 2012; Anon, 2009), but are suggested to provide inad equate control of G . pallida (Trudgill et al ., 2003), the predominant of the two species in England and Wal es. Consequently, alternative nematicides and crop protection strat egies are urgently required to ensure sustainable production of the potato. This thesis report s the findings of experiments conducted (i) to evaluate the efficacy of fluensulfone, a novel molecule belonging to the fluoroalkenyl group, for control of G . pallida and (ii) to determine factors likely to influence the efficacy of fluensulfone. In all, five experiments (three as field and two as polytunnel pot experiments) determined fluensulfone soil treatments on the control of G . pallida . The field experiments were conducted in 2010 and 2011, and were undertaken in commercial p otato fields that were predominantly infested by G . pallida at Woodcote and Howle near Newport in Shropshire, England. The field experiments 1 and 2 studied the control of G . pallida by fluensulfone application at five rates (1.95, 3.00, 4.05 (full rate), 5.05 a nd 6.00 kg a.s. ha -1 ) as a 15% granular (G) formulation and a single rate (4.05 kg a.s. ha -1 ) of a 480 g L -1 emulsifiable concentrates (EC) formulation. These treatments were compared w ith the currently commercially available fosthiazate (as Nemathorin 10G) and oxam yl (as Vydate 10G) applied at their respective recommended rates of 3.00 and 5.50 kg a.s. ha -1 . An assessment of the number of nematodes found within potato roots at ca. 4 a nd 6 weeks after planting indicated that the treatments with fluensulfone had decreased t he invasions of root by G . pallida and that fluensulfone had similar effects as the fosthiazate o r oxamyl treatment. Besides the effects on the root invasions, the multiplication r ate and final population density at harvest were reduced. Overall, the application of fluensulfo ne at the full rate gave more consistent controls than the two lower rates of 1.95 and 3.00 k g a.s. ha -1 , and the data showed no significantly greater effects for the applications higher th an the full rate. Despite the clear reduction in PCN root invasion and population increase, no sign ificant improvements in plant growth and tuber yields were recorded for the fluensulfon e, as well as the two standard nematicide treatments. In 2012, a follow-up polytunnel pot expe riment (Polytunnel experiment 1) determined the effects of granular fluensulfone t reatments at 1.95, 4.05 and 5.05 kg a.s. ha -1 on G . pallida egg viability, juvenile hatching and root invasion. The data suggested that at the studied rates, fluensulfone may be more e ffective at suppressing activities of the infective juvenile G . pallida in the soil than in eggs within cysts. The field experiment 3, at Howle in 2011, determined the integration of g ranular fluensulfone application at the full rate and partially resistant potato (Sa nté or Vales Everest) treatment on G . pallida . The results showed significant interactive effects on the mul tiplication rate and the final population density, but not on the root invasions . Furthermore, there was evidence to suggest that fluensulfone had integrated effectivel y with Santé but not with Vales Everest in controlling G . pallida population increase. In order to determine factors li kely to influence efficacy, flu ensulfone persistence and sorption on soil were investigated. The persistence studies inv olved measurements of the half-life (DT 50 ) as per the granular fluensulfone application at the full rate in the Field experiments 1 and 2, as well as in four arable soils in pot und er polytunnel conditions (Polytunnel experiment 2). The data indicated persistence no lo nger than 24 days at an incorporation depth of 15-20 cm in the fields and in the soils in the polytunnel. Fluensulfone persisted similarly as fosthiazate in the field plots. Regressi on analyses, however, could not establish a significant relationship between the DT 50 , as well as the dissipation rates constant ( k ) and soil properties. It was, t herefore, suggested that fluens ulfone had dissipated independently of the prevailing conditions. Additionally, infer ences from the reductions seen for the application of fluensulfone at the full rate on root in vasion and population build-up, suggested that the determined dissipation rates did not affect the efficacy of fluensulfone. The sorption measurements were made both for the technical-grad e and the granular product and were undertaken on a range of UK arable soil using the batc h equilibrium technique. The results, as per both the Freundlich and equilibrium sorptio n coefficients K F and K D , respectively, showed variable, but generally, low sorption of f luensulfone. The formulation gave a four-fold decrease in the sorption, and the difference w as due to limited availability of fluensulfone for uptakes. The pesticide mobility factor ( K OC ), likewise, was low, ranging from 64 - 115 mL Kg -1 OC. In all instances, the soil organic carbon accounted for mo st of the variations in sorption, and both the K F and K D correlated positively with soil amendments with peat. The theory that soil organic matter would constitute a limiting factor to the efficacy of fluensulfone was, however, not supported by a follo w-up polytunnel pot experiment (Polytunnel experiment 3) in 2012, which showed that the application of granular fluensulfone at the full rate had decreased root invasion by G . pallida in a peat-amended Shropshire sandy clay loam, irrespective of level of moss peat amendments. Fluensulfone analyses, as per water extraction in this experiment, showed th at the solution concentration of fluensulfone, throughout the duration of the experiment, was higher than the minimum effective concentration proposed in vitro for control of G . pallida J2 hatching and mobility. The suggestion, therefore, was that sorption may not limit avai lability of fluensulfone in the soil for nematicidal activities.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available