Author
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MUELLER WARRANT, GEORGE |
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ROSATO, S - OREGON STATE UNIVERSITY |
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Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/31/2001 Publication Date: 10/31/2002 Citation: MUELLER WARRANT, G.W., ROSATO, S.C. WEED CONTROL FOR LONG-TERM PRODUCTION OF PERENNIAL RYEGRASS SEED WITHOUT BURNING: I. RESIDUE REMOVED. AGRONOMY JOURNAL. 2002. v. 94(5). p. 1181-1191. Interpretive Summary: Field burning was a valuable tool in economic production of grass seed in perennial stands. The political decision to restrict field burning forced grass seed producers to develop new methods to deal with straw left in their fields after seed harvest and with weed seeds that germinate when rains return in the fall. Methods to remove or process the straw and herbicide treatments to control the weeds have been under development for the past decade. Major concerns that existed when this research was conducted included questions of how well herbicide treatments would work from year to year, whether their repeated application would eventually damage crop stands, and whether certain weed species would become more of a problem over time. Volunteer crop seed was likely to be a major weed because losses of 20% or more of crop seed are common during harvest. We found that volunteer seedlings of perennial ryegrass could cause yield losses of 25% if not controlled. We also showed that timing of herbicide application relative to the germination of weed seeds in the fall was critical. Applications of particular herbicides after weeds had already begun to emerge only worked if additional rain fell within the first few days. A mechanical technique to incorporate one of the herbicides substantially improved its performance in years with unfavorable rainfall patterns. Annual bluegrass did increase over time, but only in certain treatments. Other treatments appeared to be quite effective in controlling this weed as well as controlling the volunteer crop seedlings. Technical Abstract: Grass seed production in western Oregon underwent legislatively mandated transition from open-field burning to mechanical methods of removing residues between 1990 and 1996. Research was conducted to determine (1) the efficacy of herbicide treatments, (2) whether treatments required for weed-free seed production could be reapplied annually without eventually damaging crop stands, and (3) whether weeds such as annual bluegrass and roughstalk bluegrass would increase in prevalence over time. Tests were conducted in perennial ryegrass fields sown in 1991 and maintained in production through 1994 at one site and 1995 at two sites. All herbicide treatment sequences provided good control of volunteer perennial ryegrass seedlings in the 1992-93 growing season at all three sites and in the 1994-95 growing season at one of the two remaining sites. Control in the four other cases varied widely with herbicide treatment, ranging from good for 2.2 kg/ha rake incorporated preemergence pendimethalin followed by postemergence oxyfluorfen plus diuron to very poor for postemergence only oxyfluorfen plus diuron. Perennial ryegrass seed yield was affected by herbicide treatment, primarily through competition from uncontrolled volunteer perennial ryegrass seedlings, with seedlings causing an average yield loss of 3.0 kg/ha for each 1% increase in seedling ground cover. Vacuum sweep residue removal improved weed control over bale/flail chop/rake in all tests, but seldom affected yield. Only 15% of volunteer perennial ryegrass seedlings present in herbicide-treated plots in one year survived to become "year old" plants contributing to seed yield the next. Annual bluegrass was only found in the third year at a single site, and only occurred in plots that had not been treated with pendimethalin. |
