Author
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Mueller Warrant, George |
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ROSATO, S - OSU |
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Submitted to: Crop Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/2/2005 Publication Date: 12/31/2005 Citation: Mueller Warrant, G.W., Rosato, S.C. 2005. Weed control for tall fescue seed production and stand duration without burning. Crop Science.45:2614-2628. Interpretive Summary: Effective weed control is an important component of economically successful grass seed production. Most weed control and herbicide tolerance tests are conducted either under conditions of extremely high weed pressure when crop stands have been thinned and yields already compromised or under nearly weed-free conditions with high yielding, uniform crop stands. This study was designed to measure crop tolerance and weed control efficacy over the entire life of a tall fescue stand. Three contrasting post-harvest residue management techniques were used, one in which the full straw load was retained and chopped into a fine mulch, and two in which the straw was baled off the field, followed by either aggressive removal of seed and stubble or simple flail chopping of the stubble. Most herbicide treatments achieved good control of volunteer tall fescue seedlings, with greatest differences among treatments occurring in the full straw chop condition. Roughstalk bluegrass was nearly undetectable at the beginning of the study, but developed into a severe problem in some treatments in later years of production. This weed first appeared in plots not treated with any herbicide, and then moved into adjacent plots in subsequent years. The herbicide pendimethalin was more effective in slowing the spread of this weed than other chemicals tested. Techniques used to incorporate pendimethalin through the straw allowed this herbicide to be useful in all residue management conditions. Roughstalk bluegrass was slightly more competitive than year-old volunteer tall fescue, and much more competitive than seedling volunteer tall fescue. Duration of productive stand life was strongly affected by success of herbicides in controlling weeds. Technical Abstract: 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 study was conducted to determine (i) efficacy of herbicides on volunteer tall fescue seedlings, (ii) whether treatments required for weed-free seed production could be reapplied annually without damaging stands, (iii) whether interactions between residue management systems and herbicides occurred, and (iv) whether common weeds would increase over time. Herbicide treatments were compared for four years in a commercial tall fescue field sown in 1990 and maintained in production through 1996 using residue-removed and residue-retained management. Nearly all herbicide treatments controlled volunteer tall fescue seedlings with bale-flail chop-rake residue removal, ranging from averages of 3.7% volunteer seedling ground cover in 1993 to 0.8% cover in 1995 and 1996. Vacuum sweep improved control over bale-flail chop-rake residue removal in many cases, and controlled seedlings even without herbicides in 1995. With residue-retained management, application of preemergence incorporated pendimethalin reduced volunteer seedling ground cover by 4.6-fold in 1993 and 8.4-fold in 1994. Roughstalk bluegrass (Poa trivialis L.) increased over time in some treatments, and was a major cause for reduced yields in later years of production. Roughstalk bluegrass and year-old tall fescue were 3.8 and 3.2X as competitive as seedling tall fescue. In addition to competition from roughstalk bluegrass and volunteer tall fescue, other causes for reduced yields included crop injury from herbicides and changes in crop phenology as stands aged. |
