Weed and disease incidence in no-till facultative wheat in the Pacific Northwest, USA

Abstract

Weeds and diseases are major problems in the tillage-based winter wheat (Triticum aestivum)/summer fallow (WW/SF) cropping system of the low precipitation zone (≤300 mm) of the Pacific Northwest. Computer models have estimated that no-till spring crops may reduce soil erosion susceptibility by 95%. However, these annual cropping systems were not economically viable alternatives to the WW/SF rotation. Late-planted WW, also examined as an alternative, was similarly not viable with 35% lower grain yields than WW planted at the normal seeding date for the area. In 2002, two facultative wheat (FW) rotations were incorporated into a long-term, multidisciplinary field study to compare weed and disease incidence with a WW/reduced tillage summer fallow (WW/RSF) system for 4 years. Facultative wheat, not synonymous with late-planted WW, is often derived from SW by WW crosses and exhibits strong photosensitivity and partial sensitivity to vernalization. The two FW systems compared with WW/RSF were no-till FW/no-till spring wheat (FW/SW) and no-till FW/chemical fallow (FW/ChF). Facultative wheat was planted in early-November compared to WW planted in early-September and SW in the following March. Although 16 weed species were present during the study, Bromus tectorum and Salsola tragus were the most pervasive weeds and were found at the highest densities in FW following SW (FW(SW)). Populations of B. tectorum were often 90% higher in FW(SW) than in either WW or FW following ChF. The FW/ChF, WW/RSF, and SW following FW had similarly low weed populations when averaged over 4 years. Facultative wheat had less root disease than WW throughout the study. Stripe rust (Puccinia striiformis) was severe in SW in 2005, but did not affect either FW. Based on the low weed and disease incidence coupled with the no-till planting of FW, the FW/ChF system showed promise as an alternative sustainable system to WW/SF.