Resiliency of a nematode community and suppressive service to tillage and nematicide application

Abstract

We hypothesized that populations of predatory and omnivorous nematodes would be slower to recover from conventional tillage and nematicide application than other nematode trophic groups, and that lower populations of predators and omnivores would lead to greater survival and reproduction of plant-feeding nematodes (i.e., pest resurgence). A field study was conducted from 2008 to 2010 with two tillage regimes (strip and conventional) and two nematicide treatments (1,3-dichloropropene+aldicarb and a no-nematicide control) with six replications arranged in a split-plot design. Soil samples were collected pre-fumigation/tillage, post plant, and mid season during each year. Nematodes were extracted from soil and identified to genus. The field site had relatively high populations of predatory and omnivorous nematodes and abundance of these feeding groups translated into a relatively high Structure Index (≥60) in the control plots. Tillage had little impact on the nematode community, but the nematicides reduced numbers of all trophic groups compared to the control at post plant and mid season. However, for bacterial and plant feeders, there was also a consistent lingering effect of the nematicides the following year at pre-fumigation. Omnivores and predators were not severely impacted by the nematicide treatment; populations of both groups repeatedly recovered by the following spring from the yearly application of nematicides, with the exception of predators in 2008. We used two bioassays to measure the suppressive service of the soil community: one determined survival of the reniform nematode (Rotylenchulus reniformis) and the other reproduction of Meloidogyne arenaria on peanut. Survival of R. reniformis was greater in defaunated compared to native soil indicating that the soil contained organisms that consumed nematodes. Application of nematicides led to an increase in survival of the R. reniformis from 53% in the control to 78% in treated plots at post plant, and from 55% in the control plots to 66% in treated plots at mid season. Likewise, reproduction of M. arenaria was greater in soil treated with nematicides. At post plant, survival (%) of R. reniformis was negatively correlated with abundance of predators+omnivores. Organisms other than nematodes were likely involved in the suppressive service. This was particularly evident at pre-fumigation/tillage, when survival of R. reniformis was lower in plots previously treated with nematicides than in control plots. The nematicides may have altered the soil community to allow a fungal, bacterial, or invertebrate antagonist of nematodes to increase in abundance.