Evaluation of Organic Seed Treatments for Peanut Stand Establishment.

Establishing a viable plant stand is a critical goal for organic crop production.  This is especially true for peanut (Arachis hypogaea L.), which is strongly affected by soilborne pathogens during germination and early season growth.  Experiments were conducted in 2010 and 2011 to determine the effectiveness of potential organic seed treatments for peanut (copper sulfate, copper sulfate with cola as sticking agent, and bacillus subtilis GB03) compared to untreated seed, and seed treated with a conventional fungicidal seed treatment (captan plus trifloxystrobin).  Organic management practices were maintained for all plots for the remainder of the growing season.  Stand counts were made 1, 2, 3, and 4 weeks after planting, along with mortality plant counts made at 2, 3, and 4 weeks to compare total emergence versus plants that germinated but died.  The conventional seed treatment had the highest level of emergence across all 4 weeks in both years.  The conventional treatment had 23% (2010) and 49% (2011) better stands than the untreated seed by week 4, and virtually no plant mortality.  The copper sulfate with cola treatment resulted in the poorest stands (lower than the conventional treatment by 28% in 2010 and 74% in 2011 by week 4).  Also, copper sulfate with cola delayed emergence compared to all other treatments.  Copper sulfate alone had slightly improved plant stands and less mortality than bacillus subtilis whenever differences occurred, and would be preferred as an organic seed treatment for peanut.  However, there were no differences in peanut yields in 2010 (2870-3940 kg ha^-1), when plant stands were relatively adequate (7.4-10.3 plants m^-1).  But during the much hotter and drier conditions of 2011, yields were affected as stands were much lower in all treatments (2.3-8.8 plants m^-1).  The conventional treatment (1860 kg ha^-1) yielded best, copper sulfate with cola yielded worst (660 kg ha^-1), while the other three treatments were moderate (1190-1330 kg ha^-1).  From this trial, organic peanut production would have resulted in profit in 2010 and a net revenue loss in 2011 based on yield and labor inputs for hand weeding.  Organic peanut production has potential for the southeastern U.S., but is risky when grown under adverse conditions.  Among organic seed treatments, copper sulfate alone provided the most consistent results with respect to emergence, plant stand, and plant mortality, but could not match the superior results of a conventional fungicidal seed treatment.