The impact of fertiliser applications on nematode larval numbers on pasture can be influenced by the subsequent migration of larvae from soil onto herbage.

Two trials were conducted to ascertain whether the movement of nematode larvae out of soil onto herbage could explain the relatively poor efficacy sometimes seen following treatment of pastures with larvicidal compounds which had previously shown high efficacy in vitro . A tunnel house trial compared turfs contaminated with larvae onto the herbage with turfs contaminated onto the herbage plus into the soil. The number of larvae recovered from herbage was doubled when larvae were inoculated into soil as well as deposited onto herbage. A field trial compared plots contaminated with larvae onto the herbage, with plots contaminated into the soil or both onto the herbage and into the soil. There was no difference in the number of larvae recovered from herbage between plots contaminated onto the herbage and those contaminated only into the soil, indicating that larvae migrated from soil to herbage. When plots were contaminated onto herbage plus into soil, the number of larvae recovered from herbage was approximately doubled compared to the other plots, again indicating that larvae migrated freely from soil to herbage. The number of larvae recovered from the top 50 mm of soil was highest in the surface plus soil contamination plots, lower in the soil only contaminated plots and lowest in the surface only contaminated plots. Trial results support the hypothesis that migration of larvae from soil onto herbage is a plausible explanation for the sometimes-poor efficacy of larvicidal treatments applied to herbage. Overall, the test product reduced the number of larvae recovered from herbage. • Contaminating soil with larvae increased the number recovered from herbage • Larvae migrated rapidly between soil and herbage • Soil was an important reservoir of infective larvae • Migrated larvae potentially reduced the impact of larvicidal treatment • A test fertilizer treatment reduced larval numbers on herbage