Introduction
Lowbush blueberry is an economically important fruit crop in Canada that contributed $47.4 million CAD to farm gate value in 2017 (Anonymous 2019). The plant is a rhizomatous perennial shrub (Hall et al. Reference Hall, Alders, Nickerson and Vander Kloet1979; Pritts and Hancock Reference Pritts and Hancock1984), and commercial fields are developed from natural stands (Anonymous 2019). Fields are managed under a 2-yr production cycle in which plants are pruned to ground level by flail mowing in the first year (nonbearing year) (Eaton et al. Reference Eaton, Glen and Wyllie2004) and emerged shoots flower and produce berries in the second year (bearing year) (Wood Reference Wood2004). Lack of tillage and crop rotation promotes the occurrence of perennial weeds (McCully et al. Reference McCully, Sampson and Watson1991), with the perennial grass hair fescue currently a weed of concern (Anonymous 2019).
Hair fescue is a common, caespitose (tuft-forming) perennial grass in lowbush blueberry fields. Tufts form dense sods that can reduce yield by >50% (White Reference White2019; Zhang Reference Zhang2017; Zhang et al. Reference Zhang, White, Olson and Pruski2018) and hinder mechanical harvesting. Control from PRE herbicides such as hexazinone and terbacil is limited or variable (White Reference White2019; Yarborough and Cote Reference Yarborough and Cote2014; Zhang et al. Reference Zhang, White, Olson and Pruski2018), and fall pronamide applications provide the most effective control (White Reference White2019; Yarborough and Cote Reference Yarborough and Cote2014). High pronamide cost ($500 CAD ha–1), however, limits grower adoption. Hair fescue can be suppressed with nonbearing-year POST foramsulfuron applications (White and Kumar Reference White and Kumar2017), though suppression is variable (Zhang et al. Reference Zhang, White, Olson and Pruski2018). Suppression may be improved by use of sequential glufosinate and foramsulfuron applications, though glufosinate applications of 1,005 g ai ha–1 provide greater suppression than the currently registered maximum application rate of 750 g ai ha–1 (White and Kumar Reference White and Kumar2017).
Although limited to one application of 750 g ai ha–1 per year, the current glufosinate registration for lowbush blueberry in Canada allows for use of sequential fall bearing-year and spring nonbearing-year glufosinate applications of 750 g ai ha–1. Sequential glufosinate applications improve control of many annual weed species (Aulakh and Jhala Reference Aulakh and Jhala2015; Beyers et al. Reference Beyers, Smeda and Johnson2002; Coetzer et al. Reference Coetzer, Al-Khatib and Peterson2002; Culpepper et al. Reference Culpepper, York, Batts and Jennings2000), including grass weeds such as volunteer corn (Zea mays L.) (Chahal and Jhala Reference Chahal and Jhala2015), giant foxtail (Setaria faberi Herrm.) (Wiesbrook et al. Reference Wiesbrook, Johnson, Hart, Bradley and Wax2001), wild-proso millet [Panicum miliaceum L. ssp. ruderale (Kitagawa) Tzevelev], and fall panicum (Panicum dichotomiflorum Michx.) (Van Wychen et al. Reference Van Wychen, Harvey, Vangessel, Rabaey and Bach1999), as well as some perennials such as johnsongrass [Sorghum halepense (L.) Pers.] (Johnson et al. Reference Johnson, Norsworthy and Scott2014; Landry et al. Reference Landry, Stephenson and Woolam2016). Sequential fall and spring glufosinate applications, alone or in conjunction with spring nonbearing-year foramsulfuron applications, however, have not been evaluated for hair fescue suppression in lowbush blueberry fields. The objective of this research was therefore to determine the main and interactive effects of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on hair fescue.
Materials and Methods
Study Sites and Experimental Design
The experiment was conducted in lowbush blueberry fields located at Parrsboro (45.43°N, 64.48°W) and Portapique (45.41°N, 63.72°W), NS, Canada, and was established on November 4, 2015 at Parrsboro and November 3, 2015 at Portapique. The experiment was a 2 by 2 by 2 factorial arrangement of fall glufosinate (Ignite herbicide; Bayer CropScience, Durham, NC) application (0 g ai, 750 g ai), spring glufosinate application (0 g a.i, 750 g a.i), and spring foramsulfuron (Option® 2.25 OD herbicide; Bayer CropScience Inc., Calgary, AB) application (0 g ai, 35 g ai) arranged in randomized complete block design with four blocks and 2 m by 6 m plot size at each site. Foramsulfuron was applied with a liquid nitrogen fertilizer (28% UAN) at a rate of 2.5 L ha–1. Herbicides were applied using a CO2-pressurized research plot sprayer outfitted with four Teejet 11002 XR nozzles (TeeJet Technologies, Spraying Systems Co., Springfield, PA) and calibrated to deliver a water volume of 200 L ha–1 at 276 kPa. Fall glufosinate treatments were applied on November 11, 2015 and November 10, 2015 at Parrsboro and Portapique, respectively. Spring glufosinate treatments were applied on May 13, 2016 and May 10, 2016 at Parrsboro and Portapique, respectively. Spring foramsulfuron treatments applied alone or after fall glufosinate applications were applied on May 13, 2016 and May 10, 2016 at Parrsboro and Portapique, respectively. Spring foramsulfuron treatments applied after spring glufosinate applications were applied on May 29, 2016 at Parrsboro and Portapique.
Data Collection
Data collection included hair fescue tuft density prior to treatment applications, vegetative and flowering hair fescue tuft density in summer of the nonbearing and bearing year, hair fescue flowering-tuft inflorescence number in summer of the nonbearing year, hair fescue seed production in fall of the nonbearing year, hair fescue seedling density in early summer of the bearing year, lowbush blueberry stem density, stem height, and flower bud number per stem at the end of the nonbearing year, and lowbush blueberry yield in late summer of the bearing year. Hair fescue tuft densities were determined in two 1-m by 1-m quadrats per plot. Hair fescue inflorescence number was determined on 10 randomly selected tufts per plot using a line transect method previously described (White and Kumar Reference White and Kumar2017). Hair fescue seed production was determined by collecting all inflorescences from five randomly selected hair fescue tufts in each plot and counting all seeds retained in the collected inflorescences. Hair fescue seedling densities were counted in three 30-cm by 30-cm quadrats per plot. Initial hair fescue tuft densities in treatments receiving fall bearing-year herbicide applications were determined on November 11, 2015 and November 10, 2015 at Parrsboro and Portapique, respectively. Initial hair fescue tuft densities in treatments receiving spring nonbearing-year herbicide applications were determined on April 27, 2016 at Parrsboro and Portapique. Nonbearing-year hair fescue flowering- and vegetative-tuft densities were determined on June 28, 2016 at Parrsboro and June 27, 2016 at Portapique. Nonbearing-year flowering hair fescue tuft inflorescence number was determined on July 11, 2016 at Parrsboro and July 8, 2016 at Portapique. Hair fescue inflorescences were collected for seed production estimation on October 8, 2016 at Parrsboro and October 20, 2016 at Portapique. Hair fescue seedling densities in the bearing year were determined on May 29, 2017 at Parrsboro and May 24, 2017 at Portapique. Bearing-year hair fescue flowering and vegetative tuft densities were determined on July 10, 2017 at Parrsboro and June 29, 2017 at Portapique.
Lowbush blueberry stem density was determined in three 30-cm by 30-cm quadrats per plot. Lowbush blueberry stem height and flower bud number per stem were determined on 30 randomly selected blueberry stems per plot. Stems were clipped at ground level, bagged in the field, and brought back to the lab for data collection. Lowbush blueberry yield was determined in two 1-m by 1-m quadrats per plot, and fruit was harvested using hand rakes. Lowbush blueberry stem density was determined on October 5, 2016 at Parrsboro and on October 20, 2016 at Portapique. Stem collections for height and flower bud assessment at each site occurred on these dates as well. Lowbush blueberry yield was determined on August 14, 2017 at Parrsboro and August 2, 2017 at Portapique.
Statistical Analysis
The main effects of site, fall glufosinate applications, spring glufosinate applications, spring foramsulfuron applications, and the subsequent interactions on the various response variables were determined using ANOVA in PROC MIXED in SAS for Windows (Statistical Analysis System, version 9.4, SAS Institute, Cary, NC). Main and interaction effects were modeled as fixed effects in the analysis, and blocks were modeled as a random effect. Assumptions of normality and constant variance for all analyses were assessed using PROC UNIVARIATE in SAS, and data were LOG(Y) or SQRT(Y) transformed where necessary to achieve normality and constant variance. Means separation, where necessary, was conducted using a Tukey’s test at a probability level of α < 0.05.
Results and Discussion
Treatment Effects on Hair Fescue
There was a significant effect of site on nonbearing-year flowering-tuft density (P = 0.0182), flowering-tuft inflorescence number (P < 0.0001), and flowering-tuft seed production (P < 0.0001), as well as a significant site-by-spring foramsulfuron effect on nonbearing-year flowering-tuft density (P = 0.0085) and a significant site-by-spring glufosinate (P < 0.0001) and site-by-fall glufosinate-by-spring glufosinate-by-spring foramsulfuron effect (P = 0.0211) on nonbearing-year flowering-tuft seed production. There was also a significant site effect on bearing-year total tuft density (P < 0.0001) and flowering-tuft density (P < 0.0001), as well as a significant site-by-fall glufosinate-by-spring glufosinate-by-spring foramsulfuron effect (P = 0.0481) on bearing-year total tuft density. Sites were therefore analyzed separately in the analysis.
Nonbearing-year total tuft density was only affected by fall bearing-year glufosinate applications and spring nonbearing-year foramsulfuron applications at each site (Table 1), and data were therefore pooled by these main effects for analysis. Nonbearing-year flowering-tuft density and flowering-tuft inflorescence data were affected by all main effects at each site (Table 1), and there was a significant spring nonbearing-year glufosinate-by-spring nonbearing-year foramsulfuron effect on flowering-tuft density and a significant fall bearing-year glufosinate-by-spring nonbearing-year glufosinate effect on flowering-tuft inflorescence number at Parrsboro (Table 1). These data were therefore analyzed and presented based on the full factorial analysis. Nonbearing-year flowering-tuft seed production was also affected by various main and interactive effects, and data were also analyzed and presented based on the full factorial analysis.
Table 1. P-values indicating significance of main and interactive effects of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on nonbearing-year hair fescue total tuft density, flowering-tuft density, flowering-tuft inflorescence number, and seed production in lowbush blueberry fields at Parrsboro and Portapique, NS, Canada.
a P-values obtained from an ANOVA analysis using PROC MIXED in SAS. Main and interactive effects considered significant at P < 0.05.
Bearing-year total and flowering-tuft density were not affected by any main and interactive effects at Parrsboro (Table 2). Seedling density at this site was affected by spring nonbearing-year glufosinate applications and spring nonbearing-year foramsulfuron applications (Table 2), and data were therefore pooled across these main effects for analysis. Bearing-year total tuft density at Portapique was affected by fall bearing-year glufosinate applications and spring nonbearing-year foramsulfuron applications (Table 2), and data were pooled across these main effects for analysis. Bearing-year flowering-tuft density and seedling density at Portapique were affected by all main effects, and there was a significant fall bearing-year glufosinate-by-spring nonbearing-year glufosinate-by-spring nonbearing-year foramsulfuron effect on seedling density as well (Table 2). These data were therefore analyzed and presented based on the full factorial analysis.
Table 2. P-values indicating significance of main and interactive effects of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on bearing-year hair fescue total tuft density, flowering-tuft density, and seedling density in lowbush blueberry fields at Parrsboro and Portapique, NS, Canada.
a P-values obtained from an ANOVA analysis using PROC MIXED in SAS. Main and interactive effects considered significant at P < 0.05.
Initial hair fescue tuft density at each site was 48 ± 11 and 15 ± 7 tufts m–2 at Parrsboro and Portapique, respectively. Spring foramsulfuron applications alone did not reduce nonbearing-year total tuft density at Parrsboro but did reduce total tuft density by >50% at Portapique (Table 3). Inconsistent or limited reductions in total tuft density from foramsulfuron are common (White and Kumar Reference White and Kumar2017; White Reference White2019; Zhang et al. Reference Zhang, White, Olson and Pruski2018), as this herbicide is generally only lethal to small hair fescue seedlings (White and Kumar Reference White and Kumar2017; White Reference White2018) and great variability in hair fescue tuft size exists in field populations (S.N. White, unpublished data). Lower initial tuft density at Portapique may have also improved foramsulfuron efficacy at this site relative to Parrsboro. Spring foramsulfuron applications reduced flowering-tuft density, flowering-tuft inflorescence number, and seed production at Parrsboro (Table 4) but not Portapique (Table 5). Similar inconsistency in suppression has occurred in previous research (White Reference White2019; Zhang et al. Reference Zhang, White, Olson and Pruski2018). Reasons for this are again unclear, though variability in tuft size mentioned above likely contributes to this. Hair fescue tufts also appear to exhibit variable rates of development in the spring, with coexistence of both vegetative and bolting tufts common in early spring (S.N. White, unpublished data). This variability in tuft size and development, though as yet undocumented, likely contributes to variability in herbicide efficacy that may explain differences in tuft density reductions across sites. Foramsulfuron suppression was also limited to the nonbearing year, as there were no significant main or interactive effects on bearing-year hair fescue total tuft density or flowering-tuft density at Parrsboro (Table 2; mean total and flowering-tuft density of 23 ± 1 and 16 ± 1 tufts m–2, respectively), and bearing-year total tuft density and flowering-tuft density were not reduced by foramsulfuron at Portapique (Tables 6 and 7). Bearing-year hair fescue seedling density, however, was reduced at Parrsboro (Table 8), indicating that reductions in nonbearing-year seed production by foramsulfuron (Table 4) may reduce bearing-year seedling populations. Fall bearing-year glufosinate applications reduced total tuft density at Portapique but not Parrsboro (Table 3), indicating that fall glufosinate applications may contribute to density reductions in fields with tuft density similar to that of Portapique. Nonbearing-year flowering-tuft density and seed production, however, were not reduced by fall bearing-year glufosinate applications at either site (Tables 4 and 5), and flowering-tuft inflorescence number was only reduced at Parrsboro (Table 4). Similar results were reported by White (Reference White2019), and collectively these results indicate that surviving tufts can recover and flower following fall bearing-year glufosinate applications. Spring nonbearing-year glufosinate applications did not affect nonbearing-year total tuft density at either site (Table 1) and did not reduce flowering-tuft density, flowering-tuft inflorescence number, or seed production at Portapique (Table 5). Spring nonbearing-year glufosinate applications, however, reduced both flowering-tuft density and flowering-tuft inflorescence number at Parrsboro (Table 4). Fall bearing-year and spring nonbearing-year glufosinate applications tend to exhibit variable efficacy on hair fescue (White and Kumar Reference White and Kumar2017; White Reference White2019). Our results reflect this and further confirm that fall or spring glufosinate applications alone do not provide reliable hair fescue suppression in lowbush blueberry. Suppression of established tufts was also limited primarily to the nonbearing year, as bearing-year total tuft density and flowering-tuft density were not affected by glufosinate applications at Parrsboro (Table 2) and were not reduced by fall bearing-year or spring nonbearing-year glufosinate applications at Portapique (Tables 6 and 7). Bearing-year seedling density was, however, reduced by spring nonbearing glufosinate applications at Parrsboro (Table 8). Although seed production was not reduced at this site (Table 4), spring glufosinate applications can reduce hair fescue seed viability (White and Kumar Reference White and Kumar2017), which may have contributed to reduced seedling density.
Table 3. Effect of fall bearing-year glufosinate and spring nonbearing-year foramsulfuron applications on nonbearing- year hair fescue total tuft density in lowbush blueberry fields located at Parrsboro and Portapique, NS, Canada.
a Values represent the mean ± 1 SE. Means within the same column for each site followed by the same letter are not significantly different according to a Tukey’s multiple means comparison test at P < 0.05.
Table 4. Effect of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on nonbearing-year hair fescue flowering-tuft density, flowering-tuft inflorescence number, and flowering-tuft seed production at Parrsboro, NS, Canada.
a Inflorescence number data were SQRT(Y) transformed to meet the assumptions of the variance analysis. Transformed means are presented for variance estimates and means comparison purposes, and back-transformed means are presented in parentheses.
b Seed number data were SQRT(Y) transformed to meet the assumptions of the variance analysis. Transformed means are presented for variance estimates and means comparison purposes, and back-transformed means are presented in parentheses.
c Values represent the mean ± 1 SE. Means within the same column followed by the same letter are not significantly different according to a Tukey’s multiple means comparison test at P < 0.05.
Table 5. Effect of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on nonbearing-year hair fescue flowering-tuft density, flowering-tuft inflorescence number, and flowering-tuft seed production at Portapique, NS, Canada.
a Flowering-tuft density data were LOG(Y) transformed to meet the assumptions of the variance analysis. Transformed means are presented for variance estimates and means comparison purposes, and back-transformed means are presented in parentheses.
b Flowering-tuft inflorescence number data were LOG(Y) transformed to meet the assumptions of the variance analysis. Transformed means are presented for variance estimates and means comparison purposes, and back-transformed means are presented in parentheses.
c Values represent the mean ± 1 SE. Means within the same column followed by the same letter are not significantly different according to a Tukey’s multiple means comparison test at P < 0.05.
Table 6. Effect of fall bearing-year glufosinate and spring nonbearing-year foramsulfuron applications on bearing-year hair fescue total tuft density at Portapique, NS, Canada.
a Values represent the mean ± 1 SE. Means within the same column followed by the same letter are not significantly different according to a Tukey’s multiple means comparison test at P < 0.05.
Table 7. Effect of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on bearing-year hair fescue flowering-tuft density and seedling density at Portapique, NS, Canada.
a Seedling density data were SQRT(Y) transformed to meet the assumptions of the variance analysis. Transformed means are presented for variance estimates and means comparison purposes, and back-transformed means are presented in parentheses.
b Values represent the mean ± 1 SE. Means within the same column followed by the same letter are not significantly different according to a Tukey’s multiple means comparison test at P < 0.05.
Table 8. Effect of spring nonbearing-year glufosinate and spring nonbearing-year foramsulfuron applications on bearing-year hair fescue seedling density at Parrsboro, NS, Canada.
a Values represent the mean ± 1 SE. Means within the same column for each site followed by the same letter are not significantly different according to a Tukey’s multiple means comparison test at P < 0.05.
Fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications reduced total tuft density, flowering-tuft density, and flowering-tuft inflorescence number at each site (Tables 3, 4, and 5) and reduced seed production at Portapique (Table 5). This treatment also gave more consistent hair fescue suppression across sites than spring nonbearing-year foramsulfuron applications alone (Tables 3, 4, and 5). Spring nonbearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications also reduced flowering-tuft density and flowering-tuft inflorescence number at each site (Tables 4 and 5) and reduced seed production at Portapique (Table 5). This treatment, however, did not reduce total tuft density. These results indicate that growers could consider sequential glufosinate and foramsulfuron applications to improve nonbearing-year hair fescue suppression but should use fall bearing-year rather than spring nonbearing-year glufosinate applications as a result of greater reductions in total tuft density. White and Kumar (Reference White and Kumar2017) also found that spring nonbearing-year glufosinate applications followed by foramsulfuron did not reduce total tuft density, further indicating that fall bearing-year glufosinate applications may be more effective than spring nonbearing-year applications if used in conjunction with spring nonbearing-year foramsulfuron applications. Fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications also reduced bearing-year total tuft density, flowering-tuft density, and seedling density at Portapique (Tables 6 and 7). From a practical perspective, fall bearing-year glufosinate applications are more amenable to lowbush blueberry production than spring nonbearing-year applications, as most growers balance spring nonbearing-year herbicide applications with spring bearing-year monilinia [Monilinia vaccinia-corymbosi (Reade)] and botrytis (Botrytis cinerea Pers.: Fr.) blight management (Delbridge and Hildenbrand Reference Delbridge and Hildebrand1995; Hildebrand et al. Reference Hildebrand, McRae and Lu2001) and may not have the resources to conduct additional spring herbicide applications.
Despite lack of a spring nonbearing-year glufosinate effect on nonbearing-year total tuft density (Table 1), sequential fall bearing-year and spring nonbearing glufosinate applications reduced flowering-tuft density and flowering-tuft inflorescence number at each site (Tables 4 and 5) and reduced seed production at Portapique (Table 4). This glufosinate use pattern therefore seems to provide better hair fescue suppression than a single spring glufosinate application of 1,005 g ha–1, as this application rate did not reduce total tuft density or flowering-tuft density (White and Kumar Reference White and Kumar2017). Fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications, however, consistently reduced total tuft density in addition to flowering-tuft density and flowering-tuft inflorescence number (Tables 3, 4, and 5), indicating that fall bearing-year glufosinate applications should be followed by spring nonbearing-year foramsulfuron applications rather than spring nonbearing-year glufosinate applications. Sequential fall bearing-year and spring nonbearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications were also similar in efficacy to fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications (Tables 4 and 5), again indicating that fall bearing-year glufosinate applications alone are adequate if followed by spring nonbearing-year foramsulfuron applications.
Treatment Effects on Lowbush Blueberry
There were no significant main or interactive effects on lowbush blueberry stem density, stem height, flower bud number, or yield at Parrsboro (Table 9). Average stem density, stem height, flower bud number, and yield at this site were 410 ± 10 stems m–2, 18 ± 0.5 cm, 7.5 ± 0.5 buds per stem, and 2,038 ± 126 kg ha–1, respectively. There were also no significant main or interactive effects on lowbush blueberry stem density or height at Portapique (Table 9), and stem density and height averaged 289 ± 10 stems m–2 and 16 ± 1 cm, respectively. There was, however, a significant spring nonbearing-year glufosinate effect on lowbush blueberry flower bud number and a significant fall bearing-year glufosinate and spring nonbearing-year glufosinate effect on lowbush blueberry yield at Portapique (Table 9). Data were therefore pooled by these effects for analysis. There was a significant spring nonbearing-year glufosinate effect on lowbush blueberry flower bud number (P < 0.0001), with flower bud number increasing from 4.7 ± 0.3 buds per stem in the absence of spring glufosinate applications to 6.3 ± 0.3 buds per stem following spring glufosinate applications (t = –5.97; P < 0.0001). Sequential fall bearing-year and spring nonbearing-year glufosinate applications also increased yield at Portapique relative to no glufosinate applications (Table 10). Results indicate that suppression of hair fescue increased yield at Portapique. Significance of glufosinate in the yield response may be linked to the injury it causes to weeds relative to foramsulfuron. Glufosinate injury is characterized by fairly rapid necrosis of treated leaf tissue (Anderson et al. Reference Anderson, Swanton, Hall and Mersey1993; Takano et al. Reference Takano, Beffa, Preston, Westra and Dayan2019). Similar injury occurs to hair fescue (White and Kumar Reference White and Kumar2017; White Reference White2018). Although not fatal to large tufts, this injury does reduce the existing hair fescue canopy until regrowth occurs (White and Kumar Reference White and Kumar2017). In contrast, foramsulfuron injury consists primarily of stunting and reduced overall growth, but treated plants maintain the leaf canopy present at the time of herbicide application (White and Kumar Reference White and Kumar2017). This difference in injury, particularly during spring of the nonbearing year when new blueberry shoots are emerging, may contribute to differential yield responses between these herbicides. In addition, new lowbush blueberry stems emerge from both rhizomes as well as lateral buds at the base of previously pruned stems (White et al. Reference White, Boyd and Van Acker2012). New shoots emerging from these lateral buds emerge before those arising from rhizomes (White et al. Reference White, Boyd and Van Acker2012) but yield fewer flower buds than those emerging from rhizomes (Ismail and Hanson Reference Ismail and Hanson1982). Spring glufosinate applications may have killed the new shoots emerging from lateral buds, providing a “chemical pruning” effect that may have stimulated growth of new shoots from rhizomes, as the uneven terrain at the Portapique site did result in uneven cutting height of blueberry stems during pruning (S.N. White, personal communication).
Table 9. P-values indicating significance of main and interactive effects of fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications on lowbush blueberry stem density, stem height, flower buds per stem, and yield in lowbush blueberry fields at Parrsboro and Portapique, NS, Canada.
a P-values obtained from an ANOVA analysis using PROC MIXED in SAS. Main and interactive effects considered significant at P < 0.05.
Table 10. Effect of fall bearing-year and spring nonbearing-year glufosinate applications on lowbush blueberry yield at Portapique, NS, Canada.
a Values represent the mean ± 1 SE. Means within the same column for each site followed by the same letter are not significantly different according to a Tukey’s multiple means comparison test at P < 0.05.
In conclusion, fall bearing-year glufosinate applications, spring nonbearing-year glufosinate applications, and spring nonbearing-year foramsulfuron applications alone did not consistently reduce hair fescue total tuft density, flowering-tuft density, flowering-tuft inflorescence number, or seed production, and any suppression obtained was limited to the nonbearing year only. Fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications, however, reduced total tuft density, flowering-tuft density, and flowering-tuft inflorescence number at each site and reduced seed production at Portapique. This treatment also reduced bearing-year seedling density, providing evidence that damage to hair fescue in the nonbearing year can reduce seedling density in the subsequent bearing year. Spring nonbearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications were less effective than fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications, suggesting that growers should use fall bearing-year glufosinate applications if considering use of sequential glufosinate and foramsulfuron applications for hair fescue management. Fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications were also more effective than sequential fall bearing-year and spring nonbearing-year glufosinate applications and provided efficacy similar to sequential fall bearing-year and spring nonbearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications. Results therefore indicate that fall bearing-year glufosinate applications followed by spring nonbearing-year foramsulfuron applications are likely the best combination of these particular herbicides for hair fescue management in lowbush blueberry.
Acknowledgments
We acknowledge field assistance from Hugh Lyu, Cody Webb, Lienna Hoeg, and Tyler Jollimore. Field sites for this research were provided by Milford Welton and Joe Slack. Funding for this research was provided by the Wild Blueberry Producers Association of Nova Scotia, Dalhousie University, and the Nova Scotia Department of Agriculture through a Research Acceleration Grant (grant no. RA15-0009) to S.N.W. No conflicts of interest have been declared.
