2006 Annual Report 4d.Progress report. This report serves to document research conducted under a specific cooperative agreement between ARS and North Dakota State University. This project was initiated in June 2005 and activities are ongoing. The objectives of this project are to characterize the spatial development of Sclerotinia stem rot (SSR) epidemics under North Dakota conditions; evaluate the relationship between strength of the source of inoculum and the creation of spatial disease gradients by SSR epidemics; and to evaluate post-infection environmental conditions that promote SSR epidemic development. Please refer to the report for project 5442-21220-010-00D, Sclerotinia Diseases, for additional information. In 2005, field experiments were established at three locations to study the spatial characteristics of epiphytotics caused by Sclerotinia sclerotiorum in canola. A disease gradient that tapered off with distance was observed. Highest disease severity was observed at the edge of the experimental area (0 m from a source of inoculum) and decreased with distance from the source. Regression equations indicated that disease severity was reduced at a rate ranging from 0.5 to 1% per meter; however, disease incidence was reduced at less than 0.5% per meter. This means that a buffer area of approximately 40 m would result in a reduction of disease severity of 20 to 40%, which could eliminate the need for a fungicide application in areas away from the source. This suggests that significant potential exists for precision farming technology to manage Sclerotinia in commercial fields. The areas selected for the study on strength of the source produced apothecia after the flowering period ended and no data could be collected. The temporal dynamics of spore production was characterized using blue medium dishes (which is a passive sampling method), and two types of volumetric spore traps (active sampling methods) at two locations. Passive spore sampling was conducted at Cando and Langdon on the 1, 7, 9, 15, and 21 of July. Spore peaks where observed at both locations only on the first three dates when air temperature inside the canopy was on average <70o F and relative humidity was higher than 80%. Almost 90% of the spores collected daily were collected between 10 am and 2 pm. A Passive sampling method was as effective as volumetric spore traps in detecting spore populations in air. The advantage is that the passive method is considerably cheaper. Efforts to monitor ascospore populations in the air will continue in following years. These populations will be associated with weather variables as well as with disease intensity.