Effect of cultivar, carbofuran and row spacing on the incidence of stem and leaf nematodes (Ditylenchus dipsaci and Aphelenchoides ritzema-bosi) in lucerne (Medicago sativa) and on lucerne herbage yield

Abstract

SUMMARYIn a clay loam at Rothamsted, inoculated with lucerne stem nematode (Ditylenchus dipsaci) and a leaf nematode (Aphelenchoides ritzema-bosi), lucerne herbage yields were increased on average by 17 and 59% respectively, in the first and second years of a 4-year experiment (1988–91), by carbofuran granules applied around the seeds at sowing in spring 1988. In seven-row plots over the 4 years of the experiment, 1·65 kg a.i./ha increased total yield as much as did 3·3 kg a.i./ha (11 and 12%, respectively). In four-row plots over the same period, 1·9 kg a.i./ha increased total yield by 9%. The cultivars Euver and Vertus, which are partially resistant to D. dipsaci, yielded 44·3 and 48·5 t dry matter/ha, respectively, whereas Europe and Vela, which are susceptible to the nematode, yielded less (36·3 and 28·6 t/ha, respectively). When sown in summer 1990 in four-row plots, cultivars Europe and Euver yielded larger crops in 1991 in plots given 1·2 or 2·3 kg a.i. carbofuran/ha in 1990 (on average 34 and 48%, respectively) than in untreated plots. As little as 0·6 kg carbofuran/ha increased the yield of cv. Europe in infested soil.The stunting of lucerne plants, associated with D. dipsaci infestation, was greatly decreased by carbofuran, which prevented infestation of the first crop by D. dipsaci and A. ritzema-bosi. Stem nematode infestation of lucerne plots was adequately and quickly assessed by measuring the lengths of rows stunted by D. dipsaci. Other methods of assessment were laborious and no more reliable.