INFLUENCE OF FENSULFOTHION AND FENAMIPHOS ON ROOT LESION NEMATODE NUMBERS AND YIELD OF FORAGE LEGUMES

Abstract

A field study was made of the effects of three rates of fenamiphos [ethyl-3-methyl-4-(methylthio) phenyl (1-methylethyl) phosphoramidate] and fensulfothion [O,O-diethyl O-(p-(methylsulfinyl) phenyl) phosphorothioate] on root lesion nematode numbers (Pratylenchus spp.), and on forage yields of red clover (Trifolium pratense L.), alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.). Both nematicides, at the rates tested (fensulfothion − 11.2, 22.4 and 44.8 kg/ha; fenamiphos − 5.6, 11.2 and 22.4 kg/ha) reduced populations of root lesion nematodes in the soil, as well as in rootlets of the three forage legumes. Seeding year yields were increased by both nematicides. Neither nematicide resulted in substantial yield increases at the time of the the first cut (June) of the second growing season, but did result in considerably increased yields at the time of the second and third cuts. At the same rates of application, fenamiphos provided better control of nematodes than did fensulfothion, particularly with increasing time following treatment. The larger total yield increases for the two growing seasons from fenamiphos-treated plots were coincident with better root lesion nematode control. Fewer alfalfa, birdsfoot trefoil and red clover taproots were infected by Fusarium spp. and Rhizoctonia solani Kühn in fenamiphos-treated plots, where there were fewer root lesion nematodes, than in check plots. Laboratory tests indicated that field rates of fensulfothion and fenamiphos were not fungicidal to a number of soil fungi, including Fusarium spp. and R. solani, found associated with forage legume roots.