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Comparing protection afforded by different organic alternatives to conventional fungicides for reducing scab on pecan

Clive Bock: USDA ARS, Southeastern Fruit and Tree Nut Research Laboratory

<div>Pecan scab (<em>Venturia effusa</em>) is the major yield-limiting disease in the southeastern USA. Although conventional fungicides are available to manage the disease, there is no comparison of organic methods (organically produced nuts attract a higher price). In 2011, 2012, 2014, 2015 and 2016 trees of cv. Desirable were treated with Bordeaux mixture (BM), Compost tea, Sodium Bicarbonate, Serenade, Serenade + Kocide 2000, Sulfur, Nordox 75WG, or Regalia (R). Exact number of sprays depended on the year. Samples of fruit were assessed for severity of scab. Only in 2011, a dry year, did the sulfur treatment have more severe scab compared to any other treatment (F=2.9, P=0.007). The control (C), and the other treatments were not significantly different to each other. In all remaining years, the C had significantly more severe scab compared to some (2012 [F=11.6, P<0.0001], 2014 [F=14.6, P<0.0001] and 2015 [F=14.6, P<0.0001]) or all other treatments (2016 [F=15.5, P<0.0001]). Trees treated with R had less severe scab compared to the C (2012 [C = 9.7%, R = 2.81%], 2014 [C = 70.0%, R = 24.8%], 2015 [C = 22.1%, R = 4.61%] and 2016 [C = 7.18%, R = 3.22%]). BM did significantly reduce scab severity on fruit in three of five years, in 2012 (4.5%), 2015 (3.33%) and 2016 (2.27%) compared to the C. Other treatments were less consistent. Although organic fungicide options reduce scab, using resistant cultivars will be more reliable for organic pecan production in the southeastern USA.</div>