MONITORING TRENDS IN WEEDS OF GRASS SEED CROPS USING GIS TOOLS
Geographic Information System (GIS) software contains powerful tools for displaying and interpreting spatial data, but information must first be geo-referenced. Oregon Seed Services routinely collects information on production practices of certified grass seed crops, including pre-harvest inspection reports on weed presence within fields. Access to data was granted under the stipulation that grower confidentiality be maintained in any public releases of maps or other summaries. A total of 71 grassy weeds and 136 broadleaves, sedges, and other types were found in 10 years of inspections of an average of 5,801 fields per year. The primary obstacle to importing data into ArcGIS was that fields were only localized to township/range/section (TRS) position, with an average of 4.2 and a maximum of 23 unique production fields per TRS. Somewhat arbitrary latitude/longitude values were assigned to each field using a procedure maximizing distances between fields within each TRS. Raster maps were generated with Inverse Distance Weighted (IDW) methods using weed abundance values of 0, 1, 10 or 100 for ratings of absent, trace, many, or excessive numbers of each species. Subtracting rasters for one year from the next identified regions in which weeds such as Poa trivialis were changing in prevalence over time.