Characterization of early leaf spot suppression by strip tillage in peanut.

ABSTRACT Epidemics of early leaf spot of peanut (Arachis hypogaea), caused by Cercospora arachidicola, are less severe in strip-tilled than conventionally tilled fields. Experiments were carried out to characterize the effect of strip tillage on early leaf spot epidemics and identify the primary target of suppression using a comparative epidemiology approach. Leaf spot intensity was assessed weekly as percent incidence or with the Florida 1-to-10 severity scale in peanut plots that were conventionally or strip tilled. The logistic model, fit to disease progress data, was used to estimate initial disease (y(0)) and epidemic rate (r) parameters. Environmental variables, inoculum abundance, and field host resistance were assessed independently. For experiments combined, estimated y(0) was less in strip-tilled than conventionally tilled plots, and r was comparable. The epidemic was delayed in strip-tilled plots by an average of 5.7 and 11.7 days based on incidence and severity, respectively. Tillage did not consistently affect mean canopy temperature, relative humidity, or frequency of environmental records favorable for infection or spore dispersal. Host response to infection was not affected by tillage, but infections were detected earlier and at higher frequencies with noninoculated detached leaves from conventionally tilled plots. These data suggest that strip tillage delays early leaf spot epidemics due to fewer initial infections; most likely a consequence of less inoculum being dispersed to peanut leaves from overwintering stroma in the soil.