Management of weeds is often a barrier to conversion from conventional to organic agriculture. Tef is a C4 annual cereal that is valued for its small seeds, rapid establishment, and wide adaptation. The objective of this study was to evaluate tef as a smother crop for management of weeds during transition to organic production. Greenhouse and field trials were conducted in 2008 and 2009 to evaluate the growth of eight tef varieties and their effect on Canada thistle and annual weeds. In greenhouse studies, tef decreased the biomass of Canada thistle shoots and roots 44 to 74%, depending on variety. Emergence of Canada thistle shoots was affected by the planting depth of their roots. Tef variety Corvalis suppressed Canada thistle biomass and accumulated more biomass than most other tef varieties. In field studies, tef varieties suppressed annual weed biomass by 35 to 54% with varieties Corvalis, Dessie, and VA-T1 being least suppressive in 2008, but there were no differences between varieties in 2009. Canada thistle growth was suppressed an average of 73% by tef in 2008 and 37% in 2009, a year of cooler temperatures and unseasonal rainfall. Differences between varieties in suppressing Canada thistle and annual weeds were mostly inconsistent between years. However, tef variety Tiffany did consistently suppress biomass, height, and percentage cover of Canada thistle and other weeds in the field study in 2008 and 2009.
Nomenclature: Tef, Eragrostis tef (Zucc.) Trotter; Canada thistle, Cirsium arvense (L.) Scop.