Peanut (Arachis hypogaea L.) is susceptible to diseases caused by numerous soilborne pathogens. In the southwestern United States pathogens including Botrytis cinerea Pers.: Fr., Pythium spp., Rhizoctonia solani Kühn AG-4, Sclerotinia minor Jagger and Sclerotinia sclerotiorum (Lib.) de Bary, Sclerotium rolfsii Sacc., and Verticillium dahliae Kleb. routinely affect peanut yield. This region has an arid climate and peanut development is generally later than in other peanut production areas, hence the time plants are exposed to pathogens is increased. These pathogens cause similar symptoms in the field; therefore, proper diagnosis is needed so that the appropriate management strategies can be implemented.
Field experiments were conducted in 2004 and 2005 to evaluate the response of several peanut cultivars to standard and reduced-input fungicide programs under production systems which differed in the duration of crop rotation, disease history within a field, or in the presence or absence of irrigation. Effects on early leaf spot (caused by Cercospora arachidicola), late leaf spot (caused by Cercosporidium personatum), and southern stem rot (caused by Sclerotium rolfsii), pod yields, and economic returns were assessed. Standard fungicide programs were similar for both sets of experiments and included applications of pyraclostrobin, tebuconazole, azoxystrobin, or chlorothalonil. Reduced-fungicide programs, comprising combinations of the aforementioned fungicides, resulted in two and four applications for the cultivar and irrigation experiment, respectively. Two additional programs (a seven-spray chlorothalonil and a nontreated control) were included in the cultivar experiment. Fungicide programs provided adequate levels of leaf spot suppression, and stem rot incidence was similar among fungicide programs within the two management systems. In the cultivar experiment, returns were significantly lower for the reduced program compared with the full program and seven-spray chlorothalonil program; however, they were significantly higher than the nontreated control. Significant differences in leaf spot, stem rot, and yield were observed among cultivars in both experiments. Overall, leaf spot intensity was lowest for the cvs. Georgia-03L and Georgia-01R and greatest for Georgia Green and Georgia-02C. Georgia-03L, Georgia-02C, and AP-3 consistently had lower incidence of stem rot than the other cultivars. Pod yields for all cultivars were equivalent to or greater than Georgia Green in both experiments; however, the performance of reduced-fungicide programs was inconsistent.
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