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

grass (Mueller-Warrant and Brewster, 1986), common occurrences in grass seed fields. Seed laws and market Effective weed control was a major concern of Oregon grass seed expectations define allowable limits for weed seed congrowers during their recent transition from open-field burning to mechanical methods of managing post-harvest residues. This 4-yr herbitamination, but production efficiency concerns related cide by residue management study was conducted to determine: (i) to yield losses in the field and during seed cleaning can efficacy of herbicides on volunteer tall fescue (Festuca arundinacea set more stringent limits on tolerable weed density. Schreb.) seedlings and other weeds, (ii) whether treatments required Desire by western Oregon grass seed producers to minfor weed-free seed production could be reapplied annually without imize costs associated with their transition from burning damaging stands, (iii) occurrence of interactions between herbicides led to numerous innovations in production practices. and crop residue management, and (iv) increases in grassy weeds over Foremost among these was reexamination of the fundatime. Nearly all herbicide treatments controlled volunteer tall fescue mental principle that crop residues must be removed seedlings with bale/flail chop/rake residue removal. Vacuum sweep from the field after harvest to promote tiller regrowth residue removal improved control over bale/flail chop/rake in many necessary for seed production the following year (Chilcases, and controlled seedlings even without herbicides in 1995. Incorporation of pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl2,6-dinitrobecote et al., 1980). As an alternative to removal, residues nzenamine] improved weed control in bale/flail chop/rake and residuewere sometimes flail-chopped into fine mulch spread uniretained conditions. Although carryover treatment effects reduced formly over the field to decompose during the fall and weed seedling survival in later years of production and sometimes winter (Churchill et al., 1995). As equipment and procereduced tall fescue seed yield, specific treatments existed which condures were developed to efficiently chop straw and stubtrolled weeds for all 4 yr without reducing yield. Interactions beble into mulch rather than remove it, growers and retween residue management and herbicide treatments included reduced searchers pondered long-term impacts of this practice. efficacy of pendimethalin in residue-retained management, higher yields They specifically wondered how crop regrowth, soil moisat equal weed densities in residue-removed conditions, and higher weed ture, weed seed germination, herbicide performance, densities from equivalent herbicide treatments in residue-retained seed yield, and stand longevity might differ between conditions. Roughstalk bluegrass (Poa trivialis L.) increased over time in some treatments and was a major cause for reduced yields in residue-removed and residue-retained conditions. later years of production. Tall fescue seed growers must risk some Research in perennial ryegrass and tall fescue seed procurrent-year yield loss from herbicide injury to avoid greater losses duction using pendimethalin, trifluralin [2,6-dinitro-N, in future years from perennial weeds like roughstalk bluegrass. N-dipropyl-4-(trifluoromethyl)benzenamine],metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1methylethyl)acetamide], and oxyfluorfen [2-chloro-1G seed production in western Oregon under(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] went a mandatory transition between 1990 and 1996 applied as preemergence (PRE) herbicides under resifrom open-field burning to mechanical methods of redue-removed conditions determined which of several key moving or otherwise processing post-harvest residues. factors were of greatest importance for each herbicide Early research had shown that many of the yield benefits (Mueller-Warrant et al., 1994a, 1994b, 1995a, 1995b; from field burning were also provided by mechanical reMueller-Warrant, 1999; Mueller-Warrant and Rosato, moval of post-harvest residues, but achieving adequate 2002a, 2002b). PRE timing of application was most critiweed control was a concern (Young et al., 1984). Some cal for pendimethalin and trifluralin. Incorporation by studies revealed the presence of lingering yield benefits rainfall within 1 wk after application was most critical from burning, especially in later years of production for for metolachlor. Abundant moisture at the soil surface perennial ryegrass (Lolium perenne L.) and tall fescue was most critical for oxyfluorfen. Weed control generally (Young et al., 1999). However, yield differences between improved when PRE herbicide treatments were followed burn and non-burn residue management were similar by postemergence (POST) applications of diuron [N’-(3, in size to those that could be caused by uncontrolled vol4-dichlorophenyl)-N,N-dimethylurea], metribuzin [4unteer perennial ryegrass seedlings (Mueller-Warrant amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazinet al., 1994b) or by moderate densities of roughstalk blue5(4H)-one]), terbacil [5-chloro-3-(1,1-dimethylethyl)6-methyl-2,4(1H,3H)-pyrimidinedione], and/or oxyfluorfen. While preliminary tests of pendimethalin applied on top G.W. Mueller-Warrant, USDA-ARS, National Forage Seed Prod. of chopped residues were disappointing, the ability of Res. Center, 3450 SW Campus Way, Corvallis, OR 97331-8539; S.C. PRE herbicides to control seedling grasses under resiRosato, Dep. of Crop & Soil Sci., Oregon State Univ., Corvallis, OR 97330. Contribution of USDA-ARS. Received 11 Aug. 2003. *Corredue-removed conditions when even small amounts of sponding author ([email protected], [email protected]). rain moved them into the weed seed germination zone suggested that efforts to incorporate herbicides through Published in Crop Sci. 45:2614–2628 (2005). the straw might be beneficial. While diuron had been Seed Physiology, Production & Technology doi:10.2135/cropsci2003.0375 © Crop Science Society of America Abbreviations: EP, early-postemergence; INC, incorporated; LF, leaves; LP, late-postemergence; POST, postemergence; PRE, preemergence. 677 S. Segoe Rd., Madison, WI 53711 USA 2614 Published online October 27, 2005