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Hagan, A. K., Campbell, H. L., Bowen, K. L., and Wells, L. 2015. Seeding rate and planting date impacts stand density, diseases, and yield of irrigated peanuts. Plant Health Progress doi:10.1094/PHP-RS-14-0019. Release of peanut cultivars with enhanced tomato spotted wilt (TSW) resistance along with the decline in the incidence of this disease gives Alabama producers the option of earlier planting of irrigated peanuts to optimize farm operations and lower seeding rates to reduce input costs. Mid-April and mid-May plantings of the cvs. Florida-07, Georgia-06G, and Georgia Green at 6.6, 9.8, 13.1, and 19.7 seed/m were monitored over three years for TSW, stem rot, and leaf spot diseases as well as yield. Despite low TSW pressure and lack of a seeding rate response, disease incidence was higher in Georgia Green than Florida-07 and Georgia-06G with higher TSW indices noted for the April than May plantings of the former but not latter two cultivars. While not impacted by planting date, stem rot incidence, which was higher at 13.1 and 19.7 than 6.6 seed/m, was lower on Florida-07 than Georgia-06G and Georgia Green with the latter proving most susceptible. Although leaf spot intensity was not impacted by seeding rate, disease ratings were higher for May than April plantings, with Florida-07 and Georgia-06G having lower leaf spot ratings than Georgia Green in two of three study years. While planting date did not impact yield in two of three years, higher yields were recorded at 13.1 and 19.7 than 6.6 seed/m, with Florida-07 and Georgia06G having higher yields than Georgia Green. Seed accounts for up to 20% of variable production costs for peanut (Arachis hypogaea L.), particularly for the large seeded cvs. Georgia-06G and Florida-07 (Smith and Smith 2012). Reducing seeding rates is one option to help producers manage costs, particularly when peanut farm-gate prices are low. Previously, Wehtje et al. (1994.) obtained similar yields with the peanut cv. Florunner planted at 55 to 122 kg seed/ha when irrigated, while Hauser and Buchanan (1981) reported lower yield with a reduced seeding rate compared to the recommended rate of 90 kg/ha, which equates to 19.7 seed/m. Augusto et al. (2010) noted that Nicaraguan farmers could increase their gross income by reducing seeding rates but are prevented by poor seed quality. Following the appearance of the Tospovirus Tomato spotted wilt virus (TSWV) in Alabama, Florida, and Georgia peanuts in the late 1980s, significant disease intensification and yield declines were associated with reduced seeding rates of susceptible and, to a lesser extent, resistant cultivars (Branch et al. 2003; Culbreath et al. 2011; Weeks et al. 1994). Only Black et al. (2001) in Texas failed to link increased tomato spotted wilt (TSW) incidence and subsequent yield decline with reduced seeding rates. In contrast to TSW, stem rot, caused by Sclerotium rolfsii Sacc. (telemorph Athelia rolfsii (Cursii) Tu & Kimbrough), typically intensifies with increasing seeding rates (Augusto et al. 2010; Black et al. 2001). The effect of seeding rate on the intensity of early leaf spot, caused by Cercospora arachidicola Hori, and late leaf spot, caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton, has not been examined. Planting date also impacts TSW incidence in peanut. Prior to the appearance of TSW, the planting window for peanut ranged from mid-April into mid-May (Henning et al. 1982). Observations of higher TSW incidence and thrips vector populations (Weeks et al. 1994) along with thrips-related leaf damage (Weeks et al. 1992) in Aprilcompared to May-planted peanuts in Alabama were later confirmed in Georgia by Brown et al. (1996). Delaying planting into May has less of an effect on TSW incidence and yield of a resistant than susceptible cultivar (Culbreath et al. 2010; Tillman et al. 2007). As a result of the TSW epiphytotic that began in the early 1990s, producers were advised to delay planting until mid-May (Brown et al. 2003; Brown et al. 2005; Hagan and Weeks 1993). Beginning with cv. Southern Runner (Black and Smith 1987; Weeks et al. 1994), runner market type peanut cultivars with constantly improving TSW resistance and yield potential have been released (Branch 1996; Branch 2007; Brown et al. 2005; Culbreath et al. 2011; Culbreath et al. 2010; Gorbet et al. 2009; Tillman et al. 2007). In 2010, Culbreath et al. (2010) noted that the level of resistance is sufficient in newly released cultivars to advance planting into April without elevating the risk of a TSW outbreak. Also, the marked decline in TSW incidence in Alabama in recent years (A. K. Hagan, personal observation), provides producers the opportunity to increase their April-planted peanut acreage. Stem rot incidence and subsequent yield loss is generally higher in Aprilthan May-planted peanuts (Bowen 2003; Brenneman and Hadden 1996; Hagan et al. 2001). Hagan et al. (2001) noted that disease incidence declined by nearly 50% for mid-May compared with mid-April planted peanuts. Impact of planting date on stem rot was more pronounced on the susceptible cvs. Andru 93 and Florunner than the partially resistant cv. Southern Runner, which may have matured after S. rolfsii activity in the rhizosphere peaked Corresponding author: Austin Hagan. Email: haganak@auburn.edu doi:10.1094 / PHP-RS-14-0019 © 2015 The American Phytopathological Society

Seeding Rate and Planting Date Impacts Stand Density, Diseases, and Yield of Irrigated Peanuts