GIS Analysis of Crop Rotation and Stand Age Effects on Grass Seed Weeds

Authors: Mueller Warrant, George; Whittaker, Gerald; YOUNG, WILLIAM - OREGON STATE UNIVERSITY

Submitted to: Seed Production Research at Oregon State University
Publication Type: Experiment Station
Publication Acceptance Date: 3/31/2006
Publication Date: 4/30/2006
Citation: Mueller Warrant, G.W., Whittaker, G.W., Young, W.C. 2006. Gis analysis of crop rotation and stand age effects on grass seed weeds. Seed Production Research at Oregon State University. EXT/CrS 125, 4/06. Pages 10-13

Interpretive Summary: Research needs identified during our analysis of 10-year trends of grass seed weeds include both long-recognized problems and newly emerging concerns. Foremost among the long-recognized problems were control of roughstalk bluegrass, annual bluegrass, Italian ryegrass, and other volunteer crops. While Canada thistle has long been on the list of prohibited noxious weeds, our finding that it was the third most aggressively spreading weed of grass seed crops was surprising, and indicates a need for research to determine why and how this is occurring. Wild carrot is already the focus of considerable industry research, and our findings suggest that poor control in rotational crops and fallow periods between grass seed stands may be a key to its success as a weed. All of the weed problems highlighted as research needs are clearly also production management concerns. In addition to these concerns, however, growers, or crop production consultants advising them, must pay close attention to all 15 weeds able to increase in severity over time in established grass seed stands. Success in controlling opportunistic weeds is also important. Many possible concerns for seed certification suggested by our analysis are issues that have long been recognized as central to the effective functioning of seed certification. These would include monitoring of noxious weeds, enforcement of land history requirements for limiting varietal contamination, and identification of stands infested with excessively high populations of weeds hard to remove during seed conditioning.

Technical Abstract: Ten years (1994 to 2003) of OSU Seed Certification pre-harvest field inspection reports for 10,643 harvests from 3481 stands grown on 2779 distinct fields were georeferenced to field locations to develop a GIS of grass seed cropping history and weed distribution patterns in Linn County, Oregon. In 545 cases, new stands were planted in fields previously used to grow certified grass seed crops. In 31% of those cases, fields were replanted to the same variety as previously grown. In the other 69% of cases, growers changed crop species more often than expected for independence of prior and follow-on crops. Growers replanted fields to new grass seed stands sooner when following creeping bentgrass and fine fescue than when following Colonial bentgrass, tall fescue, and orchardgrass. Implementation of a legislatively-mandated phase-down in field burning during years overlapping with our data corresponded with a 20% reduction in average perennial ryegrass stand life. Of 22 weeds statistically shown to carryover from prior to follow-on crops, strongest correlations existed for western wildcucumber, annual bluegrass, and roughstalk bluegrass. Increasing length of time out of grass seed increased the severity of 10 weeds, most strongly in the cases of field bindweed, common groundsel, wheat, and wild carrot, and decreased the severity of four weeds (Italian ryegrass, roughstalk bluegrass, reed canarygrass, and lowland cudweed). Based on average year-to-year increases in severity with increasing stand age, the five most aggressive weeds of established perennial grass seed crops were roughstalk bluegrass, tall fescue, Canada thistle, Bromus spp., and Agrostis spp.