Improving upon the management of soilborne diseases of peanut in West Texas



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Peanut (Arachis hypogaea L.) is susceptible to numerous soilborne pathogens in the High Plains of West Texas 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. Because these pathogens may cause similar symptoms in peanut fields, accurate diagnosis is important for proper management to mitigate damages and losses caused by these pathogens. Fungicides are the primary management option for this region, and current application regimes are based on models developed in the Southeastern United States. This region has an arid climate and peanut development is generally later than in other areas of the United States. These factors impact initial fungicide application timing and may affect efficacy. The objectives of this research were to i) develop a disease diagnostic guide for peanut producers of this region, ii) evaluate fungicide application timing for pod rot and iii) quantify the residual activity of fungicides used in the management of pod rot of peanut. Large plot fungicide trials were conducted in the growing seasons of 2010 and 2011 to study the effects of delaying initial applications of fungicides, azoxystrobin, mefenoxam, and flutolanil on disease development. Initial applications were made 68 or 82 days after planting (DAP) with subsequent applications using a banded spray application. In 2010, the percentage of pods affected and percent damaged kernels were reduced by early applications of mefenoxam and azoxystrobin. The flutolanil treatment in 2010 showed the greatest improvement in yield compared to the control. The 2011 trial was greatly affected by drought, and no appreciable differences were seen for any of the parameters evaluated. In 2011, a fungicide bioassay was conducted to determine the residual activity of the fungicides azoxystrobin and flutolanil + propiconazole on the foliage and pods of the peanut cultivars GA09B and McCloud. Broadcast applications of both fungicides were made three times in the growing season using a backpack sprayer system. Plants were destructively sampled prior to fungicide application and 1, 3, 5, 7, 14, 21 and 28 days after application. A detached leaflet assay was completed using Sclerotium rolfsii as a quantitative measure. Fungicides did not show significant differences between one another, with both fungicides reducing activity of S. rolfsii as compared to the non-treated control. The residual activity of azoxystrobin and flutolanil + propiconazole ranged from 7 to 28 days. Additional testing is required to obtain a more accurate determination of residual activity of these fungicides. Despite poor environmental conditions for 2011, the studies conducted show that application timing may differ from current recommendations. Further study is needed to improve current fungicide application regimes and improve the management of soilborne disease in this region.