Effects of potential trap crops and planting date on soil infestation withpotato cyst nematodes and root-knot nematodes

In 1997 and 1998 the stimulation of hatch of potato cyst nematodes (PCN) by a trap crop was studied at various times during the growing season in a co ntainer and a field experiment. Solanum nigrum '90-4750-188' was used as th e trap crop in both experiments and was sown on 1 May, 16 June or 1 August in two successive years on different plots. Neither experiment revealed muc h seasonal variation in hatchability of PCN juveniles under a trap crop. In the container experiment, the hatch of the Globodera pallida Pa3 populatio n was equally and strongly stimulated (89%) at all sowing dates in both yea rs, except for the 1 August sowing in 1998 (when the hatch was 77% under ex tremely wet soil conditions). In the control treatment with non-hosts (flax followed by barley) the total spontaneous hatch was 50% over 2 yr. In the field experiment, the hatch of PCN, averaged over the four populations, was also equally stimulated (71%) at all sowing dates in both years. In the co ntrol treatment with non-hosts (flax barley) the total spontaneous hatch wa s 36% over 2 yr. Total hatch under the trap crop over 2 yr varied between t he four PCN populations from 63% to 80%. In 1998 and 1999, control of potato cyst nematodes (PCN) by the potential t rap crops Solanum sisymbriifolium and S. nigrum '90-4750-188' was studied i n the field. Potato was also included as a trap crop. In the 1998 experimen t, potato, S. sisymbriifolium and S. nigrum strongly stimulated the hatch o f PCN compared with the non-host white mustard (Sinapis alba). Roots of pot ato and white mustard were mainly found in the top 10 cm of soil, whereas r oots of S. sisymbriifolium and S. nigrum were also abundant at depths of 10 -20 cm and 20-30 cm. In the 1999 experiment, soil infestation with PCN decr eased markedly with potato and S. sisymbriifolium as trap crops. In plots m oderately to severely infested with 2yr old cysts (2-29 juveniles ml(-1) ai r dried soil), potato reduced soil infestation by 87% and S. sisymbriifoliu m by 77%. In plots moderately to severely infested with I-yr old cysts the reductions were 74% and 60%, respectively. The reduction was least on plots very severely infested with PCN (110-242 juveniles ml(-1) soil): 69% and 5 2% for potato and S. sisymbriifolium, respectively. Soil infestations of pl ots that were initially slightly to severely infested with the root-knot ne matode Meloidogyne hapla were greatly reduced under fallow and S. sisymbrii folium but increased under potato. From these and previous experiments it w as concluded that, for several reasons, S. sisymbriifolium is a promising t rap crop.