Fumigation of marine clay soils infested with Globodera pallida and G. rostochiensis using 1,3-dichloropropene and additional top soil treatments
Authors: Been Thomas , Schomaker Corrie 
Published: March 2012

Three fields of marine clay soil were fumigated with 150 l/ha 1,3-dichloropropene (DD) (Telone IITM, Shell 95TM). On three dates after application, concentrations of Z - and E-1,3-dichloropropene were measured per 5 cm layer of soil to a depth of 40 cm and integrals of concentration time products were calculated. When the fumigant was no longer detectable, a top soil treatment with either 150 l/ha metam-sodium or 180 kg/ha dazomet (active compound methyl isothiocyanate) was applied, followed immediately by autumn ploughing. Soil samples were taken before and after fumigation and after the top soil treatment to extract potato cyst nematodes (PCN). Survival was determined from hatching tests. Mortality after the DD treatment, defined as the complement of the percentage of survival, was estimated for each 5 cm layer of soil to a depth of 30 cm to construct dosage response curves. Fumigation with DD killed 48, 48, and 72% of the PCN per field, respectively. Accelerated breakdown of DD by micro-organisms accounted for the two lower mortality rates. The additional top soil treatment with metam-sodium increased mortality to 90% or more. Dazomet, however, was less effective (53 and 80%) considering that twice as much of the active compound was applied as in the metam-sodium treatment. Multiplication, in pot experiments, of hatched juveniles originating from the injection layer after the DD treatment was 25% less than that of those from untreated plots. This was caused by a lower fraction of juveniles developing into cysts. PCN could be retrieved from soil layers as deep as 80 cm below the surface. Fumigation reached only a fraction of the infested soil, down to 25-30 cm. The infestation foci were so small compared to the standard minimum area fumigated (1 ha) that 90% of the active compound would be wasted on non-infested soil. Soil fumigation, whether or not combined with an additional top soil treatment, will seldom be profitable. Monitoring for infestation foci is recommended. Fumigation de sols argileux d'origine marine infestes par Globodera pallida et G. rostochiensis a l'aide de 1,3 dichloropropene et d'un traitement additionnel de surface - Trois champs au sol argileux d'origine marine ont ete traites avec 150 l/ha de 1,3 dichloropropene (DD) (Telone IITM, Shell 95TM). A trois moments apres le traitement, les concentrations en Z - et E-1,3 dichloropropene ont ete mesurees dans chaque couche de sol epaisse de 5 cm jusqu'a une profondeur de 40 cm et les integrales des produits concentration/temps calculees. Lorsque le produit fumigant n'etait plus detectable un traitement de surface a ete applique a l'aide de 150 l/ha de metam-sodium ou de 180 kg/ha de dazomet (matiere active: isothiocyanate de methyle), traitement immediatement suivi par un labour d'automne. Les nematodes a kyste de la pomme de terre (PCN) ont ete extraits d'echantillons de sol preleves avant et apres fumigation ainsi qu'apres le traitement de surface. La survie des nematodes a ete chiffree a l'aide de tests d'eclosion. Le taux de mortalite (= 100 - % de survie) apres traitement au DD a ete estime pour chaque couche de sol de 5 cm d'epaisseur jusqu'a 30 cm de profondeur pour permettre l'elaboration des courbes dose/effet. La fumigation au DD a tue respectivement 48, 48 et 79% des PCN par champ. La degradation acceleree du DD par des micro-organismes est rendue responsable de la faiblesse des deux premiers taux. Le traitement additionnel de surface accroit la mortalite jusqu'a 90% et plus. Le dazomet est cependant moins efficace (53 et 80%) si l'on considere que son compose actif a ete applique a une dose double de celle du traitement au metam-sodium. Dans les experimentations en pots, le taux de multiplication des juveniles eclos provenant des couches de sol ou le DD avait ete injecte a ete de 25% inferieur a celui des temoins. La cause en est le plus faible nombre de larves se developpant dans les kystes. Les PCN peuvent etre rencontres dans le sol a des profondeurs allant jusqu'a 80 cm. La fumigation n'atteint qu'une fraction de sol, situee a 20-30 cm de la surface. Les foyers d'infestation sont si reduits par rapport a la surface traitee (1 ha) que 90% de la matiere active est gaspillee dans du sol non infeste. La fumigation du sol, combinee ou non avec un traitement de surface, sera donc rarement rentable. La prise en consideration des foyers d'infestation est recommandee.