Evaluation of Runner-Type Peanut Cultivars and Approved Fungicides for Use in Organic Production.

Organic peanut (Arachis hypogaea L.) production in the southeastern U.S. has historically been limited due to significant disease pressure.  However, new disease-resistant peanut cultivars have greatly improved the potential for organic production in recent years.  Therefore, the primary objective of this study was to assess yield potential and early and late leaf spot (Cercospora arachidicola and Cercosporidium personatum, respectively) incidence of currently available peanut cultivars under organic management.  A secondary objective was to evaluate the efficacy of organically approved fungicides for yield and control of leaf spot diseases.  Two mid-maturing runner peanut cultivars (‘Florida-07’ and ‘McCloud’) and one late-maturing cultivar (‘Georganic’) were planted in Tifton, Georgia in 2008.  Four sub-treatment fungicide effects were applied to the Florida-07 plots (untreated, copper sulfate [2.2 kg ha^-1], QRD 800 [2.8 kg ha^-1], copper sulfate [2.2 kg ha^-1] + QRD 800 [2.8 kg ha^-1]).  All McCloud and Georganic plots were untreated.  Florida-07 (untreated plots) (5428 kg ha^-1) yielded higher (p = 0.001) than McCloud (3841 kg ha^‑1) and Georganic (3300 kg ha^-1), standardized at 10% moisture.  Georganic had low leaf spot incidence (early and late), with a rating of 5.9 on the Florida 1-10 scale (46% defoliation), although not statistically different in Florida 1-10 scale rating or percent defoliation (p = 0.142 and p = 0.171, respectively) than Florida-07 (6.6; 65% defoliation) and McCloud (7.0; 71% defoliation).  Additionally, there were no significant differences in leaf spot (early and late) incidence or yield among the untreated, copper sulfate, QRD 800, and copper sulfate + QRD 800 fungicide treatments (p < 0.05).  With no significant differences in leaf spot incidence among cultivars, the higher yield and shorter maturity range of Florida-07 make it an attractive cultivar option for peanut growers interested in organic production.