Evaluation of Oxathiapiprolin for the Management of Sunflower Downy Mildew.

Downy mildew is a yield-limiting disease of sunflower, caused by the pathogen Plasmopara halstedii. Zoospore infection of root tissue shortly after planting results in systemic infection, causing postemergence damping off or severe stunting and head sterility. Although fungicide-applied seed treatments can be an effective management tool, the pathogen is resistant to phenylamide fungicides in many growing regions, and other available fungicides have limited efficacy. Oxathiapiprolin, the first member of the piperidinyl thiazole isoxazoline fungicides, was evaluated for efficacy on downy mildew in field trials conducted from 2011 to 2015 in North Dakota. Throughout the course of the study, the rate range was narrowed from active ingredient (a.i.) at 0.45 to 116.0 µg a.i. seed-1 to an optimal effective rate of 9.37 to 18.75 µg a.i. seed-1. Within that optimal range, the downy mildew incidence of sunflower planted with oxathiapiprolin-treated seed was significantly lower than the incidence in the nontreated sunflower in all 11 trials with disease pressure. Additionally, downy mildew incidence of sunflower planted with oxathiapiprolin-treated seed was significantly lower than sunflower planted with competitive commercially available fungicide-treated seed in 10 of those 11 trials. The use of oxathiapiprolin by sunflower growers is likely to reduce disease incidence and subsequent yield loss to downy mildew.

Intraspecific variation influences natural settlement of eastern oysters.

As populations decline, their intraspecific diversity also diminishes. Population decline may be exacerbated if a decrease in intraspecific diversity also reduces important ecological functions that maintain population numbers. Oyster reefs are severely overharvested, declining by ~85 % worldwide. We tested how increasing within-species diversity of eastern oysters (Crassostrea virginica) using transplants would affect recruitment of oyster larvae, a key function necessary to maintain future populations. If harvesting reduces population numbers, within-species diversity, and connectivity, then oysters may lose the ability to adapt to changing environmental conditions as well as incur lower levels of recruitment that may hasten their decline. Results from laboratory and field studies indicated that oyster larvae use chemical cues from adult oysters and not from associated fouling communities to select settlement sites. To test how increasing within-species diversity of oysters affected recruitment, we collected oysters from three distinct bay systems in Texas, USA, and compared natural settlement in treatments where all oysters were from a single bay to a mixture of all three bays. Significantly greater recruitment occurred in mixed treatments in 2010, 2011, and 2012 even though oyster recruitment varied by order of magnitude during this time. The net biodiversity effect was positive in all 3 years, indicating that increased recruitment in mixed treatments can be greater than the additive effect of the single bay treatments. Losing intraspecific diversity may reduce recruitment and lead to further declines in oyster populations, illustrating the need for understanding how intraspecific diversity influences ecological functions.