The Degradation Of Soil Applied Nematicides Used For The Control Of The Potato Cyst Nematodes Globodera rostochiensis And G. pallida

Ambrose, Emma Louise (1999). The Degradation Of Soil Applied Nematicides Used For The Control Of The Potato Cyst Nematodes Globodera rostochiensis And G. pallida. MPhil thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000ff84

Abstract

The persistence of oxamyl and the control of potato cyst nematodes (PCN), was studied at 10 sites where Vydate was applied at commercial rates. Soil and plant samples were taken at weekly intervals for 13 weeks. Oxamyl concentrations were assessed using HPLC and potato roots stained with acid fuschin to determine invasion. Oxamyl was degraded significantly faster at one site, with a complete breakdown of the chemical 21 days after application. This was correlated with warm temperatures, moist soils and a high pH of 7.0. At 4 sites PCN invasion was observed 42 days after application, however at the other sites invasion began within 21 days. No correlation between oxamyl concentrations and control was found, however a relationship to the development of the potato was observed, with earlier invasion in faster developing plants.

At 4 sites oxamyl degraded at significantly similar rates in both thé laboratory and field. These sites had shorter half-lives of 14-25 days compared to 36-42 days at the other sites. This suggested that microbial degraders were able to remain sufficiently active in stored soils, however with the other sites activity was suppressed. Soils were taken from the field before oxamyl application, and 13 weeks and 6 months after application. At six sites degradation rates increased after a second treatment, however at 4 sites no significant increase in the rate of breakdown occurred.

Total aldicarb residues degraded quicker in aldicarb treated sods, however both aldicarb and oxamyl degraded at accelerated rates in oxamyl treated and untreated soils. This was related to increased hydrolyis at the higher pH of 6.1 in the untreated soil compared to 4.7 in the treated soils. Oxamyl degraded at similar rates in the aldicarb treated and untreated soils suggesting the breakdown was by abiotic transformations of the chemical rather than microbial degradation.

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