Soybean rust (SBR), caused by the fungus Phakopsora pachyrhiza, has been a recurring problem for soybean growers in the southern United States. In some cases, growers in this region have followed a fungicide spray program consisting of two fungicide applications to protect their crop from the disease. Our study was conducted to determine how various sequential fungicide spray programs perform under the relatively high SBR pressure found in Alabama. Results from this study suggest that there are significant differences in the relative effectiveness of a program based on products used and the sequence in which they are applied. Factors such as recent weather conditions, proximity to sources of SBR, cost of available products, and an estimate of a crops yield potential should be considered when choosing a fungicide program. Accepted for publication 10 February 2009. Published 2 April 2009.

Soybean rust, caused by Phakopsora pachyrhizi Sydow, is one of the most important foliar diseases of soybean [Glycine max (L.) Merr.]. Development of rust‐resistant lines is one objective of many soybean breeding programs. Three soybean germplasm lines designated as TGx 1987–76F (Reg. No. GP‐369, PI 657702), TGx 1987–118F (Reg. No. GP‐370, PI 657703), and TGx 1987–129F (Reg. No. GP‐368, PI 657701) with resistance to P. pachyrhizi and to Xanthomonas axonopodis pv. glycines (Nakano) Vauterin, Hoste, Kersters & Swings (bacterial pustule) were selected from lines developed by the International Institute of Tropical Agriculture (IITA) in collaboration with the USDA‐ARS at the University of Illinois. These lines were derived from a tropical soybean rust‐resistant cultivar UG5, and a rust‐susceptible, high‐yielding elite breeding line, TGx 1805–31F. A total of 297 F7 lines were evaluated for rust resistance under greenhouse conditions using whole inoculated plants, in the laboratory using detached leaves, and under field conditions in Nigeria and Alabama (287 lines). Based on assessments from these various tests, these three lines have combinations of high levels of rust and bacterial pustule resistance, good agronomic traits, and adaptable maturity to the southern U.S. soybean breeding programs. Breeders will find the three lines useful as rust‐resistant parental material in rust‐prone areas.

Sorghum [Sorghum bicolor (L.) Moench] is a potential bioenergy feedstock, for which the disease threat is unknown. Impact of N rate on aboveground dry matter (ADM), total fermentable sugar concentration (°Bx), total fermentable sugar yield (TFSY), and diseases on sweet, forage, and silage/grain sorghum varieties was evaluated in 2009, 2010, and 2011 on rainfed sites in southwest Alabama. A factorial design arranged in a split plot with four replications of 22, 44, 88, and 132 kg ha -1 N as the main plot and variety as subplots was used. Dale and M81-E sweet sorghum were grown in all years, SS405 forage and NK300 silage/grain sorghum replaced Sugar Drip sweet and SS1515 silage/grain sorghum in 2010 and 2011, respectively. No significant N rate or N rate × variety interaction for any variable was noted. Variety impacted plant population, ADM, TFSY, and °Bx. Mean ADM and TFSY peaked at 32.0 Mg ha -1 for M81-E and 3.78 Mg ha -1 for Dale. Despite a lower ADM than M81-E, Dale had higher °Bx and TFSY. Sugar Drip, SS1515, and NK300 had low biomass and sugar yields. Anthracnose, rough leaf spot, and zonate leaf spot severity differed by variety. Severe anthracnose occurred on SS405 and less so on M81E, while the remaining varieties suffered limited rough leaf spot and/or zonate leaf spot damage. As potential bioenergy feedstocks for the Southeast, Dale and M-81E had comparable ADM along with higher TFSY and °Bx with restricted disease, while anthracnose poses a significant roadblock to forage sorghum feedstock utilization.

Crown rust is a common disease on winter oats in Alabama. While considered the most destructive disease of oats, little has been done in recent years, with current cultivars, to demonstrate yield losses due to crown rust. Field studies were conducted to determine the effect of fungicides and application timing on crown rust severity and yield. All fungicides reduced crown rust and improved yield. Two fungicide applications were better than a single fungicide application for reducing crown rust. Relative to yield, a single fungicide application during flag leaf development (FS 8-9) was better than a single application during head extension (FS 10.3). When compared with the non-treated control, significant yield gains were obtained with Tilt and Headline in all four years and Stratego YLD in three of four years. Fungicide programs resulted in a broad range of crown rust severities; disease levels were highly related to decreases in yield in each of four years. In two study years, ‘Coker 227’ was more damaged by crown rust, with about 10% yield loss for each unit disease, than was ‘Horizon 270,’ with 2.5 to 4.5% loss. However, in 2013, virulence patterns of the crown rust pathogen shifted and disease on Horizon 270 was greater than that on Coker 227; relative yield losses were also much lower in 2013. Accepted for publication 15 April 2016. Published 4 May 2016.

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