Title:

Weed Control for Nonburn Grass Seed Production

Investigators:

George Mueller-Warrant, USDA-ARS Research Agronomist
Stephen Griffith, USDA-ARS, Plant Physiologist
Jeffrey Steiner, USDA-ARS Research Agronomist
Donald Churchill, USDA-ARS Agricultural Engineer
Lloyd Elliott, USDA-ARS Research Microbiologist
Thomas G. Chastain, Oregon State University
Fred Crowe, Oregon State University
Gary Kiemnec, Oregon State University

Progress:

Objective 1:

Develop weed control management practices for nonburn grass seed production (residue removal or management on site) including herbicide control.

Tests conducted during the 1994-95 growing season studied the impact of residue management practices and herbicide treatments on seed yield and weed control in fourth-seed-crop stands of perennial ryegrass and tall fescue, and third-seed-crop stands of Kentucky bluegrass and orchardgrass. Residue management practices included bale/close clip and remove ("vacuum sweep"), bale/flail chop/rake, full-straw load chopped in place ("full straw load", all species except Kentucky bluegrass), and field burn (Kentucky bluegrass only).

High yielding, nearly weed-free stands of perennial ryegrass were maintained through four harvests with a combination of vacuum sweep or bale/flail/rake residue removal, shallow incorporation of preemergence pendimethalin, and a single postemergence herbicide application of oxyfluorfen plus diuron. Chopping the full straw load in place decreased perennial ryegrass tolerance to herbicides needed to control weeds. At one site, most of the herbicide treatments that were well tolerated in the first year of full straw load destroyed the stands by the end of three years of full straw load management, while similar, but less extreme trends were seen at the other site. In vacuum sweep and bale/flail/rake management, shallow incorporation of pendimethalin with a rake-tedder improved control over normal broadcast spraying. Pendimethalin was a more effective preemergence herbicide than oxyfluorfen or metolachlor. Vacuum sweep reduced volunteer perennial ryegrass stands compared to bale/flail/rake, and less herbicide was required to achieve similar levels of control. Perennial ryegrass stands in vacuum sweep or bale/flail/rake management with the best herbicide treatments were still productive after four years, and could have been maintained for at least one more year, while full straw load stands were very poor by this growing season, and should have been terminated a year sooner, making two years difference in the useful stand life between residue-removed and full straw load treatments.

Although tall fescue tolerated full straw management better than perennial ryegrass, weed density increased and tall fescue yields decreased over time compared to residue-removed plots. Roughstalk bluegrass became a serious problem in full straw load plots that did not receive aggressive herbicide treatments. Any of the herbicide treatments were sufficient to control weeds in vacuum sweep plots, whereas large differences in control between herbicide treatments existed with bale/flail/rake management. Downy brome problems increased in Kentucky bluegrass compared to the previous year, and weed competition reduced yield in the untreated checks and in ineffective treatments. Full rates of Sinbar applied preemergence were relatively effective in controlling downy brome, but caused serious crop injury, stand loss, and yield reduction compared to better treatments. The new herbicide Beacon provided fair to good control of downy brome with less crop injury than Sinbar. Split fall applications of Beacon improved control over single applications. Tank-mixes of Beacon with Sinbar appeared to reduce injury over that from Sinbar alone. Application of Pseudomonas fluorescens strain D7 injured downy brome when applied just before a snow storm in February, but not when applied in milder conditions in September, October, or December.

Objective 2:

Develop biological control of weeds using deleterious rhizobacteria.

Ten isolates of deleterious rhizobacteria were applied to a new carbon seeding of perennial ryegrass at the Hyslop Crop Science Field Lab on Feb. 3, Feb. 27, and Mar. 7,1995. The area was oversown with diuron-susceptible annual bluegrass seed at a rate of 15.5 PLS per square foot one week before the first bacteria were applied. Early germination of the annual bluegrass seed was good. However, freezing weather in mid-February killed nearly of all the bluegrass seedlings. Annual bluegrass plants between the ryegrass rows were counted in a total of 75 square feet per plot on May 9, 1995, and average stands in the untreated checks were only 6.3% of the rate sown. None of the ten bacterial isolates differed significantly from the untreated check. Annual bluegrass populations in areas not oversown were only 19% as large as those in the untreated check. There was a small effect of date of application, with annual bluegrass stands averaging 6.0% for all Mar. 7 applications, 6.9% for all Feb. 27 applications, and 8.1% for all Feb. 3 applications. Annual bluegrass populations within the carbon-band protected row were very high, and high populations between the rows should be available for testing in 1996. Perennial ryegrass showed no effects from any of the treatments.

Pseudomonas fluorescens strain D7 was applied to downy brome at the Central Oregon Agric. Research Center on Sept. 13, Oct. 17, and Dec. 21, 1994, and Feb. 7, 1995. No effects on downy brome size or numbers were seen from any of the first three applications. However, the Feb. 7 application did have a dramatic impact on the downy brome, killing 30 to 48% of the plants and stunting the survivors, reducing their height by 2 inches as if Apr. 13, 1995. Difference between application dates in downy brome response to D7 may be related to snow and freezing weather that arrived shortly after the Feb. 7 application, as this organism thrives under conditions of high moisture and near-freezing temperatures.

Objective 3:

Determine the effect of non-thermal grass residue management and legume rotation on pest and weed control, fertilizer use efficiency, and soil quality.

Objective 4:

Determine contribution of volunteer seedlings to seed yield of planted perennial grass species

Over three years, volunteer perennial ryegrass between the rows contributed an average of 8% to total yield in plots receiving standard treatments of oxyfluorfen plus diuron, and 15% in untreated checks. Highest yields were achieved by band spraying of Roundup between the rows. In untreated checks, perennial ryegrass yielded 21% less within the row than the banded Roundup treatment, and 8% less than it even when the volunteer between the rows was included. Yield is lost in untreated checks to competition between the volunteer seedlings and the crop. Yield is lost in the standard oxyfluorfen plus diuron treatment both to competition from surviving seedlings and to crop injury from the herbicides. Volunteer tall fescue between the row did not contribute to yield until the second harvest after the seedlings germinated, and then only in the untreated check. However, competition from these established volunteers caused substantial yield losses in three-year-old stands. Standard herbicide treatments to control the volunteer seedlings produced similar yields to banded Roundup in tall fescue. Volunteer fine fescue did not successfully establish in any of the treatments, but weeds such as rattail fescue did become a problem by the third year of seed production.

Publications:

Mueller-Warrant, G. W. and Neidlinger, T. J. 1994. Oxyfluorfen controls seedling grasses in established perennial grasses grown for seed. J. Appl. Seed Prod. 12:14-25.

Mueller-Warrant, G. W. 1994. Weed control in U. S. grass seed crops. International Herbage Seed Production Research Group Newsletter, No. 21, pp 7-10. 1994.

Mueller-Warrant, G. W., Young, III, W. C., and Mellbye, M. E. 1995. Residue removal method and herbicides on tall fescue seed production: I Weed control. Agron. J. 87:551-558.

Mueller-Warrant, G. W., Young, III, W. C., and Mellbye, M. E. 1995. Residue removal method and herbicides on tall fescue seed production: II. Crop tolerance. Agron. J. 87:558-562. .