Weed Control for Tall Fescue Seed Production and Stand Duration without Burning

Effective weed control was a major concern of Oregon grass seed growers during their recent transition from open-field burning to mechanical methods of managing post-harvest residues. This 4-yr herbicide by residue management study was conducted to determine: (i) efficacy of herbicides on volunteer tall fescue (Festuca arundinacea Schreb.) seedlings and other weeds, (ii) whether treatments required for weed-free seed production could be reapplied annually without damaging stands, (iii) occurrence of interactions between herbicides and crop residue management, and (iv) increases in grassy weeds over time. Nearly all herbicide treatments controlled volunteer tall fescue seedlings with bale/flail chop/rake residue removal. Vacuum sweep residue removal improved control over bale/flail chop/rake in many cases, and controlled seedlings even without herbicides in 1995. Incorporation of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl2,6-dinitrobenzenamine] improved weed control in bale/flail chop/rake and residue-retained conditions. Although carryover treatment effects reduced weed seedling survival in later years of production and sometimes reduced tall fescue seed yield, specific treatments existed which controlled weeds for all 4 yr without reducing yield. Interactions between residue management and herbicide treatments included reduced efficacy of pendimethalin in residue-retained management, higher yields at equal weed densities in residue-removed conditions, and higher weed densities from equivalent herbicide treatments in residue-retained conditions. Roughstalk bluegrass (Poa trivialis L.) increased over time in some treatments and was a major cause for reduced yields in later years of production. Tall fescue seed growers must risk some current-year yield loss from herbicide injury to avoid greater losses in future years from perennial weeds like roughstalk bluegrass.