The use of genetics and cultural practices to suppress foliar diseases of peanut and reduce fungicide requirements
Cantonwine, Emily Gayle
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Peanut is affected by a number of plant pathogens that degrade the health of foliage, including Cercospora arachidicola, the cause of early leaf spot. The standard peanut production system in Georgia (the cultivar Georgia Green, conventionally tilled field, 14-day interval fungicide schedule) is relatively expensive and may be less profitable under the new market loan system than the previous quota program. Studies were conducted to characterize the effects of enhanced host resistance and strip-tillage on foliar disease epidemics of peanut and to utilize combinations of those factors with optimal applications of fungicides for integrated management of those diseases. The onset of early leaf spot epidemics was delayed by approximately 12 days in strip-tilled plots compared to conventionally tilled plots as evidenced by fewer initial infections. The onset delay appears to be the result of fewer initial inocula, rather than the facilitation of a less favorable microclimate or induction of enhanced resistance. Less than half of disease suppression observed with strip-tillage could be attributed to the maintenance of surface residue, while little to no effect was observed for pre-plant applications of glyphosate. Suppression of early leaf spot by strip-tillage was not consistently observed in fields planted to peanut in sequential years. Severity of a new leaf spot, Florida leaf spot (FLS), peaked around 50 DAP and decreased as the season progressed. This study provided no evidence that FLS is caused by a fungal or bacterial pathogen. Components of resistance to C. arachidicola, monitored using inoculated detached leaves of Georgia Green, DP-1 and C-11-2-39, corroborated the ranking of resistance by these genotypes in the field. DP-1 and C-11-2-39 had lower infection frequencies, smaller lesion diameters and longer latent periods than Georgia Green. Integrated management of early leaf spot was comparable with 2 or 3 fewer fungicide applications to the standard system. In most cases, yields and net returns were comparable with 4, 5, or 7 applications of chlorothalonil. From these results, the integrated management of foliar diseases with enhanced host resistance and/or strip-tillage is feasible for reducing fungicide inputs, with minimal economic risk due to early leaf spot.