Weed Control for Stand Duration Perennial Ryegrass Seed Production

SEED

Weed Control for Stand Duration Perennial Ryegrass Seed Production:I. Residue Removed

George W. Mueller-Warrant* and S. Caprice Rosato

ABSTRACT Gutbrod, personal communication, 1989, on the inter-pretation of field history requirements for certified pe-Weed control was a major concern of Oregon grass seed growersrennial ryegrass; Oregon Seed Certification Service,during their transition from open-field burning to mechanical methods

of managing postharvest residues. This study aimed to determine (i) 2001). If planted rows occupy one-third of total fieldefficacy of herbicides on volunteer perennial ryegrass (Lolium perenne space, maximum allowable volunteer seedling groundL.) seedlings, (ii) whether treatments required for weed-free seed cover is 12.5% of space between planted rows. Oneproduction could be reapplied annually without damaging stands, (iii) definition for good weed control would be reduction ofwhether interactions between residue management and herbicides volunteer seedling ground cover to less than this criticaloccurred, and (iv) whether weeds would increase over time. Twelve value. Poor weed control can be defined as �30% ofherbicide treatments and two residue management systems were com-

inter-row space occupied by seedlings, and marginalpared for 3 yr in three commercial perennial ryegrass fields sowncontrol between 12.5 and 30% ground cover.in 1991. Eight preemergence followed by postemergence herbicide

Research conducted in 1989–1990 and 1990–1991treatment sequences provided good control (avg. 4% ground cover)of volunteer perennial ryegrass seedlings in the 1992–1993 growing compared the effectiveness of 14 herbicide treatmentseason at all three sites, and in 1994–1995 at one of two sites. For the sequences for volunteer perennial ryegrass and tall fescueother sites and years, control ranged from good (avg. 7% ground (Festuca arundinacea Schreb.) seedling control under twocover) for 2.2 kg a.i. ha�1 rake-incorporated preemergence pendimeth- burn and three nonburn residue management systemsalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] followed (Mueller-Warrant et al., 1994a, 1994b, 1995a, 1995b). Pen-by postemergence 0.14 kg a.i. ha�1 oxyfluorfen [2-chloro-1-(3-ethoxy- dimethalin, metolachlor [2-chloro-N-(2-ethyl-6-methyl-4-nitrophenoxy)-4-(trifluoromethyl)benzene] plus 1.3 kg a.i. ha�1 di-

phenyl)-N-(2-methoxy-1-methylethyl)acetamide], anduron [N�-(3,4-dichlorophenyl)-N,N-dimethylurea] to poor (avg. 55%oxyfluorfen applied preemergence to the autumn flushground cover) for postemergence-only 0.28 kg a.i. ha�1 oxyfluorfenof seedling grasses followed approximately 6 wk laterplus 1.8 kg a.i. ha�1 diuron. Herbicide treatments affected perennial

ryegrass seed yield, with an average yield loss of 3.2 kg ha�1 for each by postemergence diuron, oxyfluorfen plus diuron, oxy-1% increase in seedling ground cover. Vacuum sweep residue removal fluorfen plus terbacil [5-chloro-3-(1,1-dimethylethyl)-6-improved weed control over bale–flail chop–rake treatment in all methyl-2,4(1H,3H)-pyrimidinedione], and oxyfluorfentests, but increased yield only once. Annual bluegrass (Poa annua plus metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(meth-L.) occurred only in plots that had not received pendimethalin. ylthio)-1,2,4-triazin-5(4H)-one] controlled an average

of 92% of volunteer perennial ryegrass seedlings and96% of volunteer tall fescue seedlings. Substantial her-

Grass seed production in western Oregon under- bicide performance differences occurred between siteswent a mandatory phased transition from open- and years in those studies, and pendimethalin gave bet-

field burning to mechanical methods of postharvest resi- ter control in some cases than sequential pendimethalindue management between 1990 and 1996. Research in followed by oxyfluorfen plus diuron in other cases.the previous decade showed that many of the yield bene- Some of the most effective herbicide treatments, such asfits of field burning were also achieved by mechanical preemergence metolachlor followed by postemergencepostharvest residue removal, but weed control was a oxyfluorfen plus diuron, caused substantial crop damageconcern (Young et al., 1984). Seed laws and market

in some tests (Mueller-Warrant et al., 1994a , 1994b).expectations define allowable limits for weed seed con-Other research revealed the occasional presence oftamination. Minimum standards for control of volunteer

seed yield benefits from burning of perennial ryegrassperennial ryegrass seedlings set by Oregon Seed Certifi-and tall fescue, especially in the third or fourth produc-cation rules limit later-generation plants to no moretion years (Young et al., 1999). Yield differences be-than 25% of the density of the original planting (O.tween burn and nonburn residue management treat-ments were similar to those of uncontrolled volunteer

G.W. Mueller-Warrant, USDA-ARS, National Forage Seed Prod. perennial ryegrass seedlings (Mueller-Warrant et al.,Res. Center, 3450 SW Campus Way, Corvallis, OR 97331-7102; and

1994b) or moderate densities of commonly occurringS.C. Rosato, Dep. of Crop and Soil Science, Oregon State Univ.,perennial bluegrass species (Mueller-Warrant and Brew-Corvallis, OR 97330. Contribution of USDA-ARS in cooperation

with Agric. Exp. Stn., Oregon State Univ. Tech. paper no. 11749 of ster, 1986). The duration of preemergence herbicidethe latter. Received 13 Apr. 2001. *Corresponding author (muellerg@ control and efficacy after 3- to 4-wk exposure to dry soilonid.orst.edu, [email protected]). before rain were studied by Mueller-Warrant (1999). A

3- to 4-wk exposure to dry soil greatly reduced thePublished in Agron. J. 94:1181–1191 (2002).

1181

1182 AGRONOMY JOURNAL, VOL. 94, SEPTEMBER–OCTOBER 2002

used extremes in residue-removal management, with vacuumefficacy of metolachlor, slightly reduced the efficacy ofsweep providing the most thorough removal of straw, stubblependimethalin, and had intermediate impact on oxyflu-and seed, while bale–flail chop–rake management was theorfen. Pendimethalin provided longer preemergencemost commercially practical. The bulk of the crop residue wascontrol of perennial ryegrass and California bromeremoved after harvest in each year by raking into windrows(Bromus carinatus H.&A.) than metolachlor or oxy- and baling. In the bale–flail chop–rake treatment, the stubble

fluorfen. left after the first baling was flail chopped to 7-cm height,Increased reliance on herbicides during the phase- raked into windrows adjacent to the plots (Needle-Nose rake

down of field burning created a strong desire for more manufactured by Rear’s Mfg., Eugene, OR), and then re-thorough testing of herbicides that could replace field moved by baling. In the vacuum sweep treatment, stubble was

cut to 3-cm height with a flail head and blown into an enclosedburning (E. Dade, personal communication, 1992). Re-wagon for removal. Residue management treatments weresearch was funded to determine how effectively herbi-arranged as main plots in a split-plot randomized incompletecide treatments could maintain yield and nearly weed-block design with four replicates per site. Each residue man-free seed production during grass seed stand life. Theagement block was 32.9 by 12.2 m, with 4.6-m-wide alleysobjectives of this research were to: (i) evaluate the effi-between blocks.cacy of herbicide treatments on volunteer perennial rye-

grass seedlings and other weeds in residue-removal sys-Herbicide Treatmenttems, (ii) determine whether herbicide treatments could

A total of 12 herbicide treatments, including single-yearbe reapplied annually without damaging perennial rye-untreated checks for the first, second, and third growing sea-grass stands, (iii) evaluate possible interactions betweensons, were applied as subplots 2.7 m wide by 12.2 m long withinresidue-removal systems and herbicide treatments, andresidue management main plots. Herbicides were applied at(iv) determine whether common weeds such as annual243 L ha�1 under 207 kPa pressure using a commercial plotbluegrass and roughstalk bluegrass (P. trivialis L.) wouldsprayer pulled by a four-wheel all-terrain vehicle at 4.2 kmincrease over time. h�1. The spraying system included bypass agitation that wasadjusted by an MT-3000 Sprayer Monitor (Micro-Trak Sys-

MATERIALS AND METHODS tems, Eagle Lake, MN) to maintain constant delivery rate.Management practices and dates are given in Table 1, includ-Site Description and Grower Practices ing herbicide applications and weed seedling growth stageswhen treated. Shallow incorporation of pendimethalin wasTests were conducted in commercial seed production fieldsachieved by use of a rotary rake–tedder within 1 h after herbi-of ‘Pennant’ (south Willamette Valley, Tangent, OR; northcide application. Because soil was dry and hard in late summer,Willamette Valley, Amity, OR) and ‘Prelude’ (central Willa-tines on the rotary-tedder only scratched 3-mm deep grooves,mette Valley, Salem, OR) perennial ryegrass planted in Sep-with most of the dust settling back down onto the treated plot.tember 1991 and harvested the first time in July 1992. GrowersNatural rainfall was the only source of moisture at all sites inused the C band planting technique in which a conventionallyall years except the first year at Salem, where 6 mm of watertilled seedbed was prepared in late summer and seed wasalong with 140 kg ha�1 N was supplied by an application ofplanted in rows in early fall. During planting, 2.5-cm-widemunicipal sewage sludge on 7 Oct. 1992.bands of activated C were applied over the rows at 336 kg

ha�1 C in the treated zone. After planting and before cropemergence, 2.7 kg a.i. ha�1 diuron was broadcast. Soon after Harvest Techniquescrop emergence, 1.1 kg a.i. ha�1 ethofumesate [(�)-2-ethoxy-

From 1993 through 1995, plots were swathed with a modi-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate]fied commercial swather with a 1.5-m-wide head, and com-was broadcast for annual bluegrass control (Lee, 1973, 1981).bined with a small plot combine equipped with windrowSoil types were Dayton silt loam (fine, montmorillonitic, mesicpickup attachment. A 1.5-m wide section through the centerTypic Albaqualfs) at Tangent, Woodburn silt loam (fine-silty,of each plot was swathed into windrows for seed yield. Seedmixed, mesic Aquultic Argixerolls) at Salem, and a combina-was bagged and later cleaned to �99% mechanical purity withtion of Woodburn silt loam and Amity silt loam (fine-silty,an air-screen seed cleaner. Postharvest residue in each mainmixed, mesic Argiaquic Xeric Argialbolls) at Amity. Growersplot was raked into windrows, baled, and weighed to deter-used standard practices for fertilization (200 kg ha�1 N split-mine straw yield on a main plot basis. Harvest index wasapplied in early and mid-spring), disease control (three appli-determined by dividing the clean seed yield by the sum of thecations of 0.12 kg a.i. ha�1 propiconazole [1-[[2-(2,4-dichloro-precleaned seed yield and the straw yield.phenyl)-4-propyl-1,3-dioxolan-2-yl] methyl]-1H-1,2,4-triazole]

applied from early May through late June), and broadleafMeasurement of Weed Ground Coverweed control (1.1 kg a.i. ha�1 2,4-D [(2,4-dichlorophenoxy)ace-

tic acid] plus 0.28 kg a.i. ha�1 dicamba [3,6-dichloro-2-meth- In all years, weed ground cover between rows was deter-oxybenzoic acid]) applied in early spring) during all years of mined by examining 500 separate 2.5 by 2.5 cm locations perthe study. In 1992, crops were harvested by growers who subplot in late winter for presence of any volunteer perennialswathed them into windrows at physiological maturity, and ryegrass seedlings and other weeds at each location. A 6.2then combined the seed when dry. No weed density or yieldcm2 area was chosen as the sampling point in ground covermeasurements were made during the first year of seed produc-measurements because individual 5-mo old seedlings weretion because no experimental treatments were applied untillarge enough to fully occupy such an area. A metal grid definedfall 1992.a fixed pattern of 50 positions, and the grid itself was droppedat 10 random locations between the originally planted rowsPostharvest Residue Management within each subplot. The grid was dropped one time in each10% of the plot length, which generally offered four inter-Vacuum sweep and bale–flail chop–rake residue manage-

ment systems were chosen to represent the two most widely row spaces within which it could land. The fixed pattern of

MUELLER-WARRANT & CAPRICE ROSATO: WEED CONTROL FOR DURATION OF RYEGRASS: I. 1183

Table 1. Dates of management practice, weed seedling growth stages, and herbicide application by test site.

Tangent Salem† Amity

Management activity Date and growth stage Date and growth stage Date and growth stage

1992–1993 Growing seasonBale and flail chop stubble 6–10 Aug. 1992 21–25 Aug. 1992 27–28 Aug. 1992Vacuum sweep 10 Aug. 1992 25 Aug. 1992 27 Aug. 1992Pendimethalin incorporated‡ 23 Sept. 1992 (PRE-E) 24 Sept. 1992 (PRE-E) 18 Sept. 1992 (PRE-E)Preemergence herbicides applied§ 7 Oct. 1992 (PRE-E) 5 Oct. 1992 (1 leaf) 1 Oct. 1992 (1 leaf)Postemergence herbicides applied¶ 20 Nov. 1992 (3 leaf) 20 Nov. 1992 (4–5 leaf) 17 Nov. 1992 (4–5 leaf)Seedling ground cover measured 2 Mar. 1993 11–12 Mar. 1993 16 Mar. 1993Swathing 9–10 July 1993 16 July 1993 13 July 1993Combining 27–28 Aug. 1993 30 Aug.–3 Sept. 1993 17–21 Aug. 1993

1993–1994 Growing seasonBale and flail chop stubble 1–2 Sept. 1993 7–9 Sept. 1993 25–26 Aug. 1993Vacuum sweep 3 Sept. 1993 10 Sept. 1993 30 Aug. 1993Pendimethalin incorporated‡ 4 Oct. 1993 (PRE-E) 1 Oct. 1993 (PRE-E) 1 Oct. 1993 (PRE-E)Preemergence herbicides applied§ 21 Oct. 1993 (1 leaf) 22 Oct. 1993 (1 leaf) 22 Oct. 1993 (1 leaf)Postemergence herbicides applied¶ 22 Nov. 1993 (2–3 leaf) 23 Nov. 1993 (2–3 leaf) 22 Nov. 1993 (2–3 leaf)Seedling ground cover measured 14 Mar. 1994 8–10 Mar. 1994 2 Mar. 1994Swathing 9 July 1994 15 July 1994 14 July 1994Combining 16 Aug. 1994 22–24 Aug. 1994 10–11 Aug. 1994

1994–1995 Growing seasonBale and flail chop stubble 18 Aug. 1994 – 11–16 Aug. 1994Vacuum sweep 19 Aug. 1994 – 17 Aug. 1994Pendimethalin incorporated‡ 7 Oct. 1994 (1 leaf) – 12 Oct. 1994 (PRE-E)Preemergence herbicides applied§ 21 Oct. 1994 (1–3 leaf) – 24 Oct. 1994 (1 leaf)Postemergence herbicides applied¶ 28 Nov. 1994 (4 leaf) – 5 Dec. 1994 (2–3 leaf)Seedling ground cover measured 13 Mar. 1995 – 21 Mar. 1995Swathing 7–8 July 1995 – 12 July 1995Combining 31 Aug. 1995 – 9–14 Aug. 1995

† Municipal sewage sludge applied 7 Oct. 1992 at the Salem site (140 kg ha�1 N in 6 mm water).‡ Pendimethalin-incorporated treatments were applied at 1.1 and 2.2 kg a.i. ha�1.§ Preemergence herbicide treatments were pendimethalin at 2.2 kg a.i. ha�1, oxyfluorfen at 0.28 kg a.i. ha�1, and metolachlor at 1.7 kg a.i. ha�1.¶ Postemergence herbicide treatments were oxyfluorfen at 0.14 kg a.i. ha�1 plus diuron at 1.3 kg a.i. ha�1, diuron at 1.8 kg a.i. ha�1, oxyfluorfen at 0.14

kg a.i. ha�1 plus metribuzin at 0.63 kg a.i. ha�1, and oxyfluorfen at 0.28 kg a.i. ha�1 plus diuron at 1.8 kg a.i. ha�1.

50 positions within the grid sampled 1.4% of the total area RESULTS AND DISCUSSIONcovered by the grid. Techniques were similar to those de-

Residue Management � Herbicidescribed by Mueller-Warrant et al. (1994a), except for a 67%Treatment Interactionincrease in number of locations sampled per subplot. In the

second and third years of the study ground cover between An important initial question in interpreting resultsrows of year-old perennial ryegrass plants was also measured. was whether interaction occurred between residue man-

agement and herbicide treatment for any of the re-Statistical Analyses sponses in any of the eight test sites–years. The closest

such interaction came to achieving significance was vol-Data were initially analyzed using a split-split-plot designunteer seedling ground cover the third year at Amitywith test sites–years as main plots, residue management treat-

ments as subplots, and herbicides as subsubplots. However, and seed yield the first year at Tangent (Table 2). How-Bartlett’s chi-square test (Steel and Torrie, 1960) indicated ever, in both cases the interaction achieved only mar-heterogeneity of variances among sites–years for volunteer ginal significance (P � 0.10), and was therefore notseedling ground cover, perennial ryegrass seed yield, and har- presented in tabular format. A second question was howvest index. Data were therefore analyzed separately for each to present herbicide treatment results. F-test differencesyear at each site using a split-plot design. Volunteer seedling among herbicide treatments or for some planned con-and year-old perennial ryegrass ground cover between crop trasts were significant (P � 0.05) except for seed yieldrows were transformed by taking log (1 � % ground cover)

and harvest index in the third year at Amity.in all analyses of variance to correct for nonhomogeneouserror variances among treatments (Little and Hills, 1978; Steeland Torrie, 1960). The LSD (P � 0.05) was used to perform Control of Volunteer Perennial Ryegrassmeans separation tests. Means separation tests on volunteer

1992–1993 Growing Seasonperennial ryegrass seedling ground cover were conducted onlog-transformed data, which were then converted back to lin- At Tangent, average volunteer perennial ryegrassear format and expressed as percent ground cover. Single seedling ground cover with bale–flail chop–rake man-degree of freedom planned contrasts were used to characterize agement was six times higher (7.8 vs. 1.3%) than withseveral important treatment factors, including untreated vs. vacuum sweep (Table 3). At Salem, average volunteerherbicide-treated, postemergence-only vs. all other herbicide seedling ground cover with bale–flail chop–rake man-treatment sequences, pendimethalin broadcast vs. incorpo-

agement was 3.2 times higher (9.2 vs. 2.9%) than withrated, and pendimethalin alone vs. pendimethalin followedvacuum sweep. At Amity, average volunteer seedlingby postemergence treatments. Analyses of covariance wereground cover with bale–flail chop–rake managementconducted to adjust perennial ryegrass seed yield for effectswas 2.1 times higher (8.6 vs. 4.1%) than with vacuumof volunteer seedling ground cover and year-old plant ground

cover (Little and Hills, 1978). sweep.


Table 2. F-values from analyses of variance for perennial ryegrass volunteer seedling ground cover, clean seed yield, and harvest indexfor all test sites–years.

Volunteer seedlingSource of variation df ground cover Clean seed yield Harvest index

Tangent, 1992–1993 growing season F-valuesResidue management 1 228.14*** 5.80† 0.26(ns)Herbicide 11 31.86*** 1.67(ns) 1.77†Contrast: untreated vs. all herbicides 1 273.36*** 9.77** 9.49**Residue management � herbicide 11 0.75(ns) 1.80† 1.61(ns)

Salem, 1992–1993 growing seasonResidue management 1 47.86** 0.11(ns) 0.30(ns)Herbicide 11 19.58*** 1.28(ns) 1.31(ns)Contrast: untreated vs. all herbicides 1 165.21*** 0.19(ns) 0.55(ns)Residue management � herbicide 11 1.56(ns) 1.20(ns) 1.22(ns)

Amity, 1992–1993 growing seasonResidue management 1 6.84† 0.32(ns) 8.77†Herbicide 11 9.29*** 1.18(ns) 1.24(ns)Contrast: untreated vs. all herbicides 1 81.53*** 6.66* 6.72*Residue management � herbicide 11 0.71(ns) 0.37(ns) 0.30(ns)

Tangent, 1993–1994 growing seasonResidue management 1 45.88** 1.04(ns) 6.17†Herbicide 11 33.85*** 29.84*** 32.88***Contrast: untreated vs. all herbicides 1 76.41*** 123.84*** 147.53***Residue management � herbicide 11 0.93(ns) 1.33(ns) 1.26(ns)

Salem, 1993–1994 growing seasonResidue management 1 43.63** 0.81(ns) 0.56(ns)Herbicide 11 40.94*** 4.59*** 5.32***Contrast: untreated vs. all herbicides 1 169.09*** 15.15*** 20.68***Residue management � herbicide 11 1.61(ns) 0.93(ns) 0.88(ns)

Amity, 1993–1994 growing seasonResidue management 1 951.94*** 25.82* 0.01(ns)Herbicide 11 29.50*** 2.63** 2.94**Contrast: untreated vs. all herbicides 1 139.26*** 2.21(ns) 3.31†Residue management � herbicide 11 0.92(ns) 1.38(ns) 1.42(ns)

Tangent, 1994–1995 growing seasonResidue management 1 10.68* 3.05(ns) 0.33(ns)Herbicide 11 14.77*** 2.62** 2.84**Contrast: untreated vs. all herbicides 1 31.77*** 3.32† 5.18*Residue management � herbicide 11 0.85(ns) 0.83(ns) 0.92(ns)

Amity, 1994–1995 growing seasonResidue management 1 243.04*** 0.22(ns) 0.40(ns)Herbicide 11 46.79*** 1.43(ns) 1.34(ns)Contrast: untreated vs. all herbicides 1 276.55*** 2.57(ns) 3.44†Residue management � herbicide 11 1.93(ns) 0.64(ns) 0.47(ns)

* Significant F-test at 0.05 probability level.** Significant F-test at the 0.01 probability level.*** Significant F-test at the 0.001 probability level.† Significant F-test at the 0.10 probability level. Main plot (residue management) and subplot (herbicide treatment) error degrees of freedom were 3 and 66.

Volunteer perennial ryegrass seedling ground cover at any site. When applied following preemergence orincorporated pendimethalin, postemergence treatmentsin current year untreated checks averaged 37% at Tan-

gent, 23% at Salem, and 40% at Amity (Table 3). All controlled an average of 49, 27, and 39% of the re-maining volunteer perennial ryegrass at Tangent, Salem,herbicide treatments reduced volunteer seedling ground

cover. Postemergence-only 0.28 kg a.i. ha�1 oxyfluorfen and Amity, respectively (percentage control is calcu-lated from ground cover treatment contrast means inplus 1.8 kg a.i. ha�1 diuron was less effective than other

herbicide treatments at Tangent and Salem, but equally Table 3). The most effective herbicide treatment at Tan-gent and Amity was preemergence pendimethalin fol-effective at Amity. Pendimethalin without follow-up

postemergence treatment controlled 90, 76, and 81% of lowed by postemergence oxyfluorfen plus metribuzin,while the most effective treatment at Salem was pre-volunteer perennial ryegrass at Tangent, Salem, and

Amity, respectively. Percentage control is calculated as emergence metolachlor followed by postemergence di-uron. The only treatment that failed to meet seed certifi-the average reduction in volunteer perennial ryegrass

seedling ground cover for pendimethalin preemergence- cation standards was postemergence-only oxyfluorfenplus diuron under bale–flail chop–rake management atonly and pendimethalin incorporated-only relative to

the untreated check. Tangent and Amity.At Tangent, there were no seedlings emerged when

Tangent: 100% � {1 � [(3.6 � 3.6)/2]/36.8} preemergence herbicides were applied on 7 Oct. 1992(Table 1). There was also no rainfall in the next 10-dSalem: 100% � {1 � [(5.9 � 5.1)/2]/22.7}period, which was then followed by 25 mm of rain fromAmity: 100% � {1 � [(6.8 � 8.4)/2]/39.7}19 October through 22 October (Fig. 1). Preemergenceherbicides worked well under these conditions. WeedIncorporation of pendimethalin did not improve control


Table 3. Ground cover of volunteer perennial ryegrass seedlings among residue management and herbicide treatments at three sites inOregon from 1993 through 1995.

1992–1993 1993–1994 1994–1995

Main effects Tangent Salem Amity Tangent Salem Amity Tangent Amity

Residue management treatments % ground coverVacuum sweep 1.3a† 2.9a 4.1a 20.7a 13.7a 8.5a 17.7a 2.3aBale–flail chop–rake 7.8b 9.2b 8.6a 38.5b 29.0b 25.3b 33.9b 15.6b

PRE/POST herbicide treatment (kg a.i. ha�1 )‡Pendimethalin 2.2 PRE/no POST 3.6d 5.9de 6.8c 45.8c 32.0d 23.8d 43.6d 5.7bPendimethalin 2.2 INC/no POST 3.6d 5.1cd 8.4c 11.6a 13.7b 11.2b 18.8b 5.7bPendimethalin 2.2 PRE/oxyfluorfen 0.14 � diuron 1.3 POST 2.3bcd 4.0abc 5.4abc 42.9c 18.3bc 12.3b 25.1bc 2.6aPendimethalin 1.1 INC/oxyfluorfen 0.14 � diuron 1.3 POST 2.8bcd 4.5cd 5.8bc 18.7b 17.5bc 12.8bc 22.7bc 6.3bPendimethalin 2.2 INC/oxyfluorfen 0.14 � diuron 1.3 POST 1.7ab 3.1ab 5.1abc 7.7a 7.7a 4.9a 6.8a 2.8aOxyfluorfen 0.28 PRE/oxyfluorfen 0.14 � diuron 1.3 POST 3.2cd 5.7cde 3.1ab 46.8c 30.7d 19.1cd 24.1bc 3.3aMetolachlor 1.7 PRE/diuron 1.8 POST 2.8bcd 2.8a 3.3ab 38.4c 21.2c 16.7bcd 20.8bc 7.9bPendimethalin 2.2 PRE/oxyfluorfen 0.14 � metribuzin 0.63 POST 1.1a 4.4bcd 2.6a 45.8c 22.8cd 14.3bc 27.8c 3.7ano PRE/oxyfluorfen 0.28 � diuron 1.8 POST 7.9e 7.9e 5.9bc 74.1d 53.3e 38.2e 53.6d 27.4cCurrent year untreated check 36.8f 22.7f 39.7d 89.7d 89.4f 72.3f 55.6d 49.6dFuture year untreated check§ 2.1bc 4.4cd 5.4bc 10.6a 8.1a 6.8a – –Past year untreated check§ – – – 11.7a 5.6a 5.0a 18.5b 3.7a

Treatment contrastsUntreated check 36.8 22.7 39.7 89.7 89.4 72.3 55.6 49.611-treatment mean 2.7 4.6 5.0 24.9 16.9 12.7 22.3 5.2

Significance *** *** *** *** *** *** *** ***no PRE/oxyfluorfen 0.28 � diuron 1.8 POST 7.9 7.9 5.9 74.1 53.3 38.2 53.6 27.410-treatment mean 2.4 4.3 4.9 22.3 15.0 11.4 20.4 4.3

Significance *** *** NS *** *** *** *** ***Pendimethalin 2.2 PRE ]2-treatment mean] 2.9 4.9 6.1 44.3 24.2 17.2 33.1 3.9Pendimethalin 2.2 INC [2-treatment mean] 2.5 4.0 6.6 9.5 10.3 7.5 11.4 4.0

Significance NS NS NS *** *** *** *** NSPendimethalin 2.2 [PRE an INC]/no POST 3.6 5.5 7.6 23.3 21.0 16.4 28.7 5.7Pendimethalin 2.2 [PRE and INC]/5-POST-treatment mean 1.8 4.0 4.6 18.2 10.8 7.9 17.6 3.3

Significance *** ** * * *** *** ** ***

* Significant F-test at 0.05 probability level.** Significant F-test at the 0.01 probability level.*** Significant F-test at the 0.001 probability level.† Means followed by the same letter do not differ at the P � 0.05 level within residue management main plot or herbicide application subplot treatments.‡ PRE, preemergence; INC, incorporated immediately after preemergence application; POST, postemergence.§ Untreated checks received 2.2 kg a.i. ha�1 incorporated pendimethalin followed by 0.14 kg a.i. ha�1 oxyfluorfen plus 1.3 kg a.i. ha�1 diuron postemergence

during years before or after the untreated year.

Fig. 1. Precipitation patterns at Tangent during the 1992–1993, 1993–1994, and 1994–1995 growing seasons.


Fig. 2. Precipitation patterns at Salem during the 1992–1993, 1993–1994, and 1994–1995 growing seasons.

control was nearly as good at Salem and Amity as it calculated as the average reduction in volunteer peren-had been at Tangent, despite the fact that seedlings nial ryegrass seedling ground cover for pendimethalinhad already begun to emerge when the preemergence preemergence-only and pendimethalin incorporated-herbicides were applied on 5 October at Salem and 1 only relative to the untreated check). Incorporation ofOctober at Amity (Table 1). Preemergence herbicides pendimethalin improved control at all sites, with anat Salem and Amity were probably activated in the first average of 64% less volunteer seedling ground cover.two days after application by 6 mm of irrigation from When applied following preemergence or incorporatedan application of city sewage sludge at Salem (Fig. 2 pendimethalin, postemergence treatments controlled anand Table 1) and 10 mm of rainfall at Amity (Fig. 3). average of 22, 48, and 52% of the remaining volunteer

perennial ryegrass at Tangent, Salem, and Amity, re-1993–1994 Growing Season spectively (percentage control is calculated from ground

cover treatment contrast means in Table 3). The mostAt Tangent, average volunteer perennial ryegrasseffective herbicide treatment at all three sites was incor-seedling ground cover with bale–flail chop–rake man-porated pendimethalin at 2.2 kg a.i. ha�1 followed byagement was 1.9 times higher (38.5 vs. 20.7%) than withpostemergence oxyfluorfen plus diuron. Only 1, 2, andvacuum sweep (Table 3). At Salem, average volunteer3 out of 12 bale–flail chop–rake treatments met seedseedling ground cover with bale–flail chop–rake man-certification standards at Tangent, Salem, and Amity.agement was 2.1 times higher (29.0 vs. 13.7%) than withIn contrast, 5, 6, and 9 out of 12 vacuum sweep treat-vacuum sweep. At Amity, average volunteer seedlingments met standards at Tangent, Salem, and Amity.ground cover with bale–flail chop–rake management

Herbicide performance in the 1993–1994 growing sea-was three times higher (25.3 vs. 8.5%) than with vac-son was much poorer than in the previous year, withuum sweep.an average of 9.2, 3.7, and 2.5 times higher volunteerVolunteer perennial ryegrass seedling ground coverperennial ryegrass seedling ground cover in herbicide-in untreated checks averaged 90% at Tangent, 89%treated plots at Tangent, Salem, and Amity, respec-at Salem, and 72% at Amity (Table 3). All herbicidetively, than in the previous year (Table 3). A late Augusttreatments reduced volunteer seedling ground cover.1993 rainfall that germinated seedlings from cracks inPostemergence-only 0.28 kg a.i. ha�1 oxyfluorfen plusthe soil, especially at Tangent and Salem, probably con-1.8 kg a.i. ha�1 diuron was less effective than othertributed to these results. The absence of rainfall duringherbicide treatments. Pendimethalin without follow-upthe following 8 wk kept those very early germinatingpostemergence treatment controlled 74, 76, and 77%seedlings from developing much beyond a 1- to 2-leafof volunteer perennial ryegrass seedlings at Tangent,

Salem, and Amity, respectively (percentage control is growth stage, but many of them were still alive when


Fig. 3. Precipitation patterns at Amity during the 1992–1993, 1993–1994, and 1994–1995 growing seasons.

rainfall next occurred in mid-October (Fig. 1 and 2). growth stage of the mid-October germinating seedlingswhen postemergence treatments were applied in lateSeedling survival during this 8-wk period was probably

enhanced by certain physical properties of the germina- November. These larger seedlings followed the patterntion sites. Before the late August rainfall, cracks in the of cracks in the soil, were visible from late August on-soil extended down to approximately 15 cm, and both ward, and survived most of the preemergence herbicideseed and straw collected in the cracks. Water from the treatments applied in October.late August rainfall ran down into those cracks, and thecracks partially closed up after the August rain, creating 1994–1995 Growing Seasonfavorable sites for seed germination and seedling sur-

At Tangent, average volunteer perennial ryegrassvival. Preemergence pendimethalin, metolachlor, andseedling ground cover with bale–flail chop–rake man-oxyfluorfen were applied to dense stands of volunteeragement was 1.9 times higher (33.9 vs. 17.7% groundseedlings predominantly in a 1-leaf growth stage 1 wkcover) than with vacuum sweep (Table 3). At Amity,after the mid-October rains began. Unfortunately, veryaverage seedling ground cover with bale–flail chop–rakelittle rainfall occurred in the first month after thesemanagement was 6.8 times higher (15.6 vs. 2.3% groundapplications. Indeed, rainfall in the first week after ap-cover) than with vacuum sweep.plication totaled only 1 mm at Tangent, 3 mm at Salem,

Volunteer perennial ryegrass seedling ground coverand 2 mm at Amity. Pendimethalin performed muchin untreated checks averaged 56% at Tangent and 50%more poorly than in the previous year, especially atat Amity (Table 3). All herbicide treatments reducedTangent, where preemergence pendimethalin followedvolunteer seedling ground cover at Amity. Postemer-by oxyfluorfen plus diuron resulted in 43% volunteergence-only 0.28 kg a.i. ha�1 oxyfluorfen plus 1.8 kg a.i.seedling ground cover between the rows, which repre-ha�1 diuron was less effective than other herbicide treat-sented only 52% control relative to the untreated check.ments. Two treatments failed to reduce volunteer seed-The postemergence-only treatment of 0.28 kg a.i. ha�1

ling ground cover at Tangent, preemergence-only pendi-oxyfluorfen plus 1.8 kg a.i. ha�1 diuron achieved onlymethalin and postemergence-only oxyfluorfen plus17, 40, and 47% control at Tangent, Salem, and Amity,diuron. Pendimethalin without follow-up postemer-respectively, in contrast to its average control of 76%gence treatment controlled 48 and 88% of volunteerthe previous year. One possible explanation for poorerperennial ryegrass seedlings at Tangent and Amity, re-performance by the postemergence treatments in thisspectively (percentage control is calculated as the aver-second growing season, especially at Tangent, was theage reduction in volunteer perennial ryegrass seedlingpresence of seedlings that had germinated in August

and were developed well beyond the 2- to 3-leaf average ground cover for pendimethalin preemergence-only and


pendimethalin incorporated-only relative to the un- tional rainfall in the final 2 wk before application wastreated check). Incorporation of pendimethalin im- 11 and 32 mm at Amity and Tangent, respectively. Vol-proved control at Tangent but not Amity. When applied unteer seedlings were still in a 1-leaf growth stage atfollowing preemergence or incorporated pendimethalin, Amity on 24 October, while they ranged from a 1-leafpostemergence treatments controlled an average of 39 growth stage for newly emerged seedlings to a 2- to 3-and 43% of the remaining volunteer perennial ryegrass leaf growth stage for older ones at Tangent on 21 Octo-seedlings at Tangent and Amity, respectively. The most ber. Indeed, seedlings had been in a 1-leaf growth stageeffective herbicide treatment at Tangent was incorpo- at Tangent when incorporated pendimethalin was ap-rated pendimethalin at 2.2 kg a.i. ha�1 followed by post- plied on 7 October. Rainfall in the week after preemer-emergence oxyfluorfen plus diuron. The most effective gence applications was 76 mm at Tangent and 116 mmtreatments at Amity were preemergence or incorpo- at Amity.rated pendimethalin at 2.2 kg a.i. ha�1 followed by post-emergence oxyfluorfen plus diuron or oxyfluorfen plus Seed Yieldmetribuzin. Only 1 out of 12 bale–flail chop–rake and

Yields for vacuum sweep and bale–flail chop–rake3 out of 12 vacuum sweep treatments met seed certifica-residue management were nearly identical in most in-tion standards at Tangent. In contrast, 5 out of 12 bale–stances, with the averages over all tests differing byflail chop–rake and 10 out of 12 vacuum sweep treat-only 9 kg ha�1 (calculated from Table 4). There was aments met seed certification standards at Amity.significant 49 kg ha�1 yield advantage to vacuum sweepHerbicide performance in the 1994–1995 growing sea-management the second year at Amity, likely due toson was similar to that of the 1993–1994 growing seasonthe threefold greater average volunteer seedling groundat Tangent and that of 1992–1993 growing season atcover under bale–flail chop–rake residue managementAmity (Table 3). One critical difference between sites(Table 3). With this sole exception, the absence of yieldwas the amount of rainfall that occurred in the lastadvantage to vacuum sweep management despite bettermonth before preemergence application (Table 1 andseedling control indicated that the vacuum sweep opera-Fig. 1 and 3). Only 5 mm of rain occurred on 29 Septem-

ber at Amity, in contrast to 51 mm at Tangent. Addi- tion itself may have injured the crop sufficiently to coun-

Table 4. Perennial ryegrass clean seed yield among residue management and herbicide treatments at three sites in Oregon from 1993through 1995.

1992–1993 1993–1994 1994–1995

Main effects Tangent Salem Amity Tangent Salem Amity Tangent Amity†

Residue management treatments seed yield, kg ha�1

Vacuum sweep 1277a‡ 1958a 1156a 1069a 1504a 1213a 1305a 1197aBale–flail chop–rake 1305a 1990a 1197a 960a 1436a 1164b 1321a 1230a

PRE/POST herbicide treatment (kg a.i. ha�1 )§Pendimethalin 2.2 PRE/no POST 1240bc 1846c 1180ab 972def 1418cde 1109e 1300a–d 1219abcPendimethalin 2.2 INC/no POST 1274abc 1929abc 1255a 1244ab 1465bcd 1116de 1317a–d 1264abPendimethalin 2.2 PRE/oxyfluorfen 0.14 � diuron 1.3 POST 1312ab 1995abc 1172ab 1033cd 1537abc 1234abc 1258bcd 1270abPendimethalin 1.1 INC/oxyfluorfen 0.14 � diuron 1.3 POST 1290ab 2056a 1105ab 1224ab 1500abc 1117de 1302a–d 1229abcPendimethalin 2.2 INC/oxyfluorfen 0.14 � diuron 1.3 POST 1299ab 1972abc 1163ab 1342a 1605a 1191b–e 1356abc 1183abcOxyfluorfen 0.28 PRE/oxyfluorfen 0.14 � diuron 1.3 POST 1299ab 1976abc 1185ab 991de 1364de 1255ab 1361ab 1297aMetochlor 1.7 PRE/diuron 1.8 POST 1329a 1873bc 1166ab 854f 1490a–d 1143b–e 1341abc 1225abcPendimethalin 2.2 PRE/oxyfluorfen 0.14 � metribuzin 0.63 POST 1332a 2089a 1189ab 908ef 1507abc 1216a–e 1297a–d 1122cno PRE/oxyfluorfen 0.28 � diuron 1.8 POST 1289ab 2034ab 1222a 706g 1327e 1224a–d 1211d 1146bcCurrent year untreated check 1201c 1948abc 1045b 563h 1296e 1131cde 1236cd 1141bcFuture year untreated check¶ 1311ab 1986abc 1217a 1183b 1590ab 1315a – –Past year untreated check¶ – – – 1151bc 1545abc 1212a–e 1388a 1232abc

Treatment contrastsUntreated check 1201 1948 1045 563 1296 1131 1236 114111-treatment mean 1299 1976 1188 1056 1486 1194 1320 1220

Significance ** NS * *** *** NS # NSno PRE/oxyfluorfen 0.28 � diuron 1.8 POST 1289 2034 1222 706 1327 1224 1211 114610-treatment mean 1300 1971 1185 1091 1502 1191 1331 1228

Significance NS NS NS *** *** NS * NSPendimethalin 2.2 PRE [2-treatment mean] 1276 1921 1176 1003 1478 1172 1279 1245Pendimethalin 2.2 INC [2-treatment mean] 1287 1951 1209 1293 1535 1154 1337 1224

Significance NS NS NS *** NS NS NS NSPendimethalin 2.2 [PRE and INC]/no POST 1257 1888 1218 1108 1442 1113 1309 1242Pendimethalin 2.2 [PRE and INC]/5-POST-treatment mean 1313 2006 1192 1123 1557 1234 1337 1208

Significance * * NS NS ** *** NS NS

* Significant F-test at 0.05 probability level.** Significant F-test at the 0.01 probability level.*** Significant F-test at the 0.001 probability level.† F-tests of differences among herbicide treatments and single degree of freedom planned contrasts were nonsignificant at Amity in the 1994–1995 grow-

ing season.‡ Means followed by the same letter do not differ at the P � 0.05 level within residue management main plot or herbicide application subplot treatments.§ PRE, preemergence; INC, incorporated immediately after preemergence application; POST, postemergence.¶ Untreated checks received 2.2 kg a.i. ha�1 incorporated pendimethalin followed by 0.14 kg a.i. ha�1 oxyfluorfen plus 1.3 kg a.i. ha�1 diuron postemergence

during years before or after the untreated year.# Significant F-test at the 0.10 probability level.


teract most of the weed control benefits. Vacuum sweep in the third year at Tangent, where the untreated checksplots were often slower to regrow in early fall, and from previous growing seasons were the highest yieldingsome of the most severely “scalped” areas within plots treatments, averaging 1388 kg ha�1. These plots receivedremained thin and stunted into early spring. the most effective herbicide treatment, incorporated

Treatments that resulted in establishment of large pendimethalin followed by oxyfluorfen plus diuron, innumbers of volunteer perennial ryegrass seedlings were all years except for whichever one they were the un-generally the lowest yielding treatments. These treat- treated check. Pooled over all tests harvested in thements included the current-year untreated checks in all final 2 yr, analysis of covariance estimated the yieldcases except the first year at Salem, the postemergence- benefit from 1-yr-old plants as being 11.7 kg ha�1 moreonly oxyfluorfen plus diuron treatment the second year seed for each 1% increase in ground cover by 1-yr-at Tangent and Salem and the third year at Tangent, old plants. This value could imply that 1-yr-old plantspreemergence pendimethalin without any follow-up contributed an average of 35 kg ha�1 seed to the totalpostemergence treatment the second year at all sites, average production of 1240 kg ha�1 for 1994 and 1995and four of the seven remaining treatments the second (calculated as 11.7 kg ha�1 � 3.0% avg. 1-yr-old groundyear at Tangent (Table 4). Analysis of covariance was cover).conducted to determine what proportion of the varia-tion in seed yield among treatments was due to competi- Harvest Indextion from uncontrolled volunteer seedlings. Addition-

Harvest index generally followed similar trends toally, this analysis was used to determine any treatmentthose seen in seed yield (Tables 4 and 5). Indeed, witheffects remaining after adjusting for seedling groundone minor exception the statistical separation of treat-cover differences, and to estimate the yield loss per unitment means for harvest index in the first growing seasonseedling ground cover.at all sites was identical to that for seed yield. The rangeAnalysis of covariance on data pooled over all eightbetween the best and worst treatments tended to betests reduced the sums of squares for herbicide treat-smaller for harvest index than for seed yield. For exam-ment by 85%, but only reduced the sums of squares forple, in the second year at Tangent, the ratio of the seedsite–year � herbicide treatment interaction by 27%.yields of the highest to lowest yielding treatments wasThese results confirmed that many of the herbicide2.38 times, while the ratio of harvest indices for thetreatment effects on seed yield were actually competi-same two treatments was only 2.05 times. Narrowingtion from uncontrolled volunteer seedlings. Results also

indicated that important residual differences among of the range between best and worst treatments alsoherbicide treatments within individual tests remained occurred in all other tests, although to a lesser extentafter removing the effects of competition. Likely causes than in the second year at Tangent. The simplest expla-for the remaining differences included variable competi- nation for a narrower range in harvest index than intiveness of volunteer seedlings in individual tests, direct seed yield was that treatments that reduced seed yieldinjury to the crop by some herbicide treatments, and also tended to reduce total aboveground biomass. Anbenefits in some years from establishment of seedlings alternate formulation of this concept would be thatin previous years. Instances where herbicide treatment whatever damage was done to perennial ryegrass plantsinjury may have been responsible for reduced crop seed by the treatments—whether mechanical injury by theyield included pendimethalin followed by oxyfluorfen vacuum sweep, destruction of leaves and tillers by herbi-plus metribuzin the third year at Amity and metolachlor cides, or competition between seedlings and establishedfollowed by diuron the first year at Salem and the second plants—this damage had more effect on vegetativeyear at Tangent. growth than on reproductive allocation.

First year results at Salem differed from those in theseven other tests, with a small increase in seed yield Long-Term Changes in Weed Populationsin that test as volunteer ground cover increased. This

Because of its universal presence, one weed speciesunexpected response may have been a consequence ofthat must be considered in any examination of weedfertilizing with high rates of sewage sludge the previouspopulation changes over time would be the volunteerfall, which led to such rank growth by the establishedcrop. The density of volunteer perennial ryegrass seed-crop plants that volunteer seedlings were covered bylings inherently varied from year to year, based on seedthe lush crop canopy and unable to compete effectivelyshatter before, during, and after swathing, on lossesfor light. It is also possible that some of the competitionduring combining, and on removal of seed from the soilbetween seedlings and the established crop at all sites–surface by equipment such as the vacuum sweep andyears was for N, and the high levels of N present inanimals such as the gray-tailed vole (Microtus canicau-the fall and winter the first year at Salem helped todus). Despite the potential of these factors to alter theavoid losses caused by competition for N. Analysis ofdensity of volunteer perennial ryegrass seedlings, thecovariance for data pooled from the seven sites otherobserved ground cover in no-herbicide checks in ourthan Salem estimated the impact of volunteer seedlingstudies ranged from a low of 12% with vacuum sweepground cover on perennial ryegrass seed yield as a lossthe first year at Salem to a high of 94% with bale–flailof 3.2 kg ha�1 for each 1% increase in ground cover.chop–rake the second year at the same site, approxi-The clearest example of the benefits 1 yr from success-

ful establishment of seedlings in previous years occurred mately an eightfold difference. Herbicide treatments


Table 5. Perennial ryegrass harvest index among residue management and herbicide treatments at three sites in Oregon from 1993through 1995.

1992–1993 1993–1994 1994–1995

Main effect means Tangent Salem Amity Tangent Salem Amity Tangent Amity

Residue management treatments seed yield as % of total harvested dry matterVacuum sweep 19.5a‡ 26.2a 16.8a 16.1a 15.9a 13.8a 14.6a 12.5aBale–flail chop–rake 20.3a 25.0a 17.7a 13.7a 15.3a 13.8a 14.4a 12.3a

PRE/POST herbicide treatment (kg a.i. ha�1 )§Pendimethalin 2.2 PRE/no POST 19.2bc 24.4c 17.3ab 14.5cd 15.2cde 12.9e 14.4abc 12.4abcPendimethalin 2.2 INC/no POST 19.6abc 25.1abc 18.2a 17.7ab 15.6bcd 13.0de 14.5abc 12.7abcPendimethalin 2.2 PRE/oxyfluorfen 0.14 � diuron 1.3 POST 20.2ab 25.8abc 17.0ab 15.2c 16.3abc 14.2abc 14.0bc 12.9abPendimethalin 1.1 INC/oxyfluorfen 0.14 � diuron 1.3 POST 19.9ab 26.4a 16.4ab 17.4ab 15.9abc 13.1cde 14.4abc 12.5abcPendimethalin 2.2 INC/oxyfluorfen 0.14 � diuron 1.3 POST 20.0ab 25.6abc 17.1ab 18.7a 16.8a 13.8b–e 14.9ab 12.1abcOxyfluorfen 0.28 PRE/oxyfluorfen 0.14 � diuron 1.3 POST 19.9ab 25.8abc 17.2ab 14.8cd 14.8de 14.5ab 15.1ab 13.1aMetolachlor 1.7 PRE/diuron 1.8 POST 20.3a 24.7bc 17.1ab 13.0e 15.8a–d 13.4b–e 14.8ab 12.5abcPendimethalin 2.2 PRE/oxyfluorfen 0.14 � metribuzin 0.63 POST 20.4a 26.6a 17.5a 13.7de 15.9abc 14.3ab 14.4abc 11.8bcno PRE/oxyfluorfen 0.28 � diuron 1.8 POST 20.0ab 26.1ab 17.9a 11.1f 14.4ef 14.1a–d 13.6c 11.9bcCurrent year untreated check 18.8c 25.2abc 15.6b 9.1g 13.9f 13.1cde 13.6c 11.7cFuture year untreated check¶ 20.2a 25.8abc 17.9a 17.0b 16.7ab 15.1a – –Past year untreated check¶ – – – 16.7b 16.3ab 14.1a–d 15.2a 12.6abc

Treatment contrastsUntreated check 18.8 25.2 15.6 9.1 13.9 13.1 13.6 11.711-treatment mean 20.0 25.6 17.4 15.4 15.8 13.9 14.6 12.5

Significance ** NS * *** *** # * #no PRE/oxyfluorfen 0.28 � diuron 1.8 POST 20.0 26.1 17.9 11.1 14.4 14.1 13.6 11.910-treatment mean 20.0 25.6 17.4 15.9 15.9 13.8 14.7 12.5

Significance NS NS NS *** *** NS * NSPendimethalin 2.2 PRE [2-treatment mean] 19.7 25.1 17.2 14.9 15.8 13.6 14.2 12.7Pendimethalin 2.2 INC [2-treatment mean] 19.8 25.4 17.7 18.2 16.2 13.4 14.7 12.4

Significance NS NS NS *** NS NS NS NSPendimethalin 2.2 [PRE and INC]/no POST 19.4 24.8 17.8 16.1 15.4 13.0 14.5 12.6Pendimethalin 2.2 [PRE and INC]/5-POST-treatment mean 20.2 25.9 17.5 16.3 16.4 14.3 14.7 12.4

Significance * * NS NS ** *** NS NS

* Significant F-test at 0.05 probability level.** Significant F-test at the 0.01 probability level.*** Significant F-test at the 0.001 probability level.† F-tests of differences among herbicide treatments and single degree of freedom planned contrasts were nonsignificant at Amity in the 1994–1995

growing season.‡ Means followed by the same letter do not differ at the P � 0.05 level within residue management main plot or herbicide application subplot treatments.§ PRE, preemergence; INC, incorporated immediately after preemergence application; POST, postemergence.¶ Untreated checks received 2.2 kg a.i. ha�1 incorporated pendimethalin followed by 0.14 kg a.i. ha�1 oxyfluorfen plus 1.3 kg a.i. ha�1 diuron postemergence

during years before or after the untreated year.# Significant F-test at the 0.10 probability level.

themselves caused up to 33-fold differences in volunteer on the soil surface, or if they were applied to seedlingsin a one-leaf growth stage when such applications wereseedling ground cover within individual test sites–years.

Annual bluegrass was found at low densities in some followed by timely rainfall. A 10-mm rainfall within thefirst week after application to seedlings in the one-leafof the plots the final year of the experiment at Tangent.

None of the pendimethalin treatments contained annual growth stage was adequate for good herbicide perfor-mance. Performance of pendimethalin was improved bybluegrass. There were an average of 5.5 more annual

bluegrass plants m�2 in the preemergence metolachlor very shallow incorporation. Control was usually im-proved when preemergence herbicides were followedfollowed by diuron treatment than in the pendimethalin

treatments (significant at P � 0.05). An annual bluegrass by postemergence treatments, but postemergence treat-ments seldom controlled more than 50 to 75% of thedensity of 5.5 plants m�2 was approximately 1000 times

lower than that found in some production fields (Muel- seedlings present at application. Uncontrolled volunteerperennial ryegrass seedlings reduced seed yield duringler-Warrant, unpublished data, 1995–1998).their first year of growth, but contributed to yield duringsubsequent years.CONCLUSIONS

Weeds were adequately controlled throughout the REFERENCESnormal 4-yr life of perennial ryegrass seed production

Lee, W.O. 1973. Clean grass seed crops established with activatedfields using either vacuum sweep or bale–flail chop–rakecarbon bands and herbicides. Weed Sci. 21:537–541.

residue management if suitable herbicide treatments Lee, W.O. 1981. Control of annual bluegrass (Poa annua ) in perennialwere applied. Suitable herbicide treatments generally ryegrass (Lolium perenne ) seed fields. Weed Sci. 29:444–447.

Little, T.M., and F.J. Hills. 1978. Agricultural experimentation: Designincluded both preemergence and postemergence com-and analysis. John Wiley & Sons, New York.ponents. Pendimethalin, metolachlor, and oxyfluorfen

Mueller-Warrant, G.W. 1999. Duration of control from preemergencefunctioned as satisfactory preemergence herbicides if herbicides for use in nonburned grass seed crops. Weed Tech-they were applied immediately before the onset of rains nol. 13:439–449.

Mueller-Warrant, G.W., and B.D. Brewster. 1986. Control of roughstalkthat germinate volunteer perennial ryegrass seed laying


bluegrass (Poa trivialis ) in perennial ryegrass (Lolium perenne ) Oregon Seed Certification Service. 2001. Oregon seed certificationgrown for seed. J. Appl. Seed Prod. 4:44–51. service handbook 2001. Oregon State Univ. Ext. Service, Cor-

Mueller-Warrant, G.W., W.C. Young III, and M.E. Mellbye. 1994a. vallis, OR.Influence of residue removal method and herbicides on perennial Steel, R.G.D., and J.H. Torrie. 1960. Principles and procedures ofryegrass seed production: I. Weed control. Agron. J. 86:677–684. statistics. McGraw-Hill Book Co., New York.

Mueller-Warrant, G.W., W.C. Young III, and M.E. Mellbye. 1994b. Young III, W.C., M.E. Mellbye, and T.B. Silberstein. 1999. ResidueInfluence of residue removal method and herbicides on perennial management of perennial ryegrass and tall fescue seed crops.ryegrass seed production: II. Crop tolerance. Agron. J. 86:684–690. Agron. J. 91:671–675.Mueller-Warrant, G.W., W.C. Young III, and M.E. Mellbye. 1995a.

Young III, W.C., H.W. Youngberg, and D.O. Chilcote. 1984. Post-Residue removal method and herbicides for tall fescue seed produc-harvest residue management effects on seed yield in perennialtion: I. Weed control. Agron. J. 87:551–558.grass seed production: I. The long-term effect from non-burningMueller-Warrant, G.W., W.C. Young III, and M.E. Mellbye. 1995b.techniques of grass seed residue removal. J. Appl. Seed Prod. 2:Residue removal method and herbicides for tall fescue seed produc-

tion: II. Crop tolerance. Agron. J. 87:558–562. 36–40.

Documents

Weed Control for Stand Duration Perennial Ryegrass Seed Production