Moss Competition Dynamics and Suppression Technologies in Wild Blueberry Production

Abstract

Increasing moss pressures have been observed in wild blueberry fields, which have been attributed to increased precipitation, reliance of fertilizers to provide adequate yield potential, and increasing soil organic matter content. This has coincided with uncertainty regarding the distribution and diversity of mosses present in fields, the competitive nature of selected mosses, and if required, effective suppression technologies. Research conducted from 2006 to 2009 indicated that mosses were present in every sampled field (n = 40), hair cap moss (Polytrichum commune) was the most prevalent moss species observed, and there was no apparent influence of blueberry canopy cover, soil texture, soil pH, or soil moisture on moss incidence. In addition, hair cap moss was observed to physically compete with the wild blueberry for space and remain actively growing late into the autumn and winter. Autumn applications of the herbicide Chateau® (a.i., flumioxazin) were observed to be very effective in suppressing hair cap moss pressures with minimal damage to the wild blueberry, and rapid wild blueberry growth occurred the following growing season.

Keywords:

• Polytrichum commune
• Vaccinium angustifolium
• competition
• control

INTRODUCTION

The lowbush (i.e., “wild”) blueberry (Vaccinium angustifolium Ait.) is an endogenous plant that has evolved into an important horticultural commodity in northeastern North America. Although commercially managed, the fields originate when competing vegetation is removed from native plant stands. The majority of wild blueberry fields are situated in acidic (soil pH between 4.2 and 5.5), marginal soils that are low in mineral nutrients, have poor water holding capacities, and a gentle-to-severe sloping topography.

Fields are commercially managed on a 2-year cycle with the perennial shoots being pruned in alternate years to maximize floral bud initiation, fruit set, yield, and ease of mechanical harvest (Percival and Sanderson, 2004). Pruned plants grow for a noncropping or “sprout” year in which vegetative growth occurs along with floral bud initiation. Selective herbicides are applied to control competing weeds in the spring of the first year and nitrogen and phosphorous fertilizers are applied. During the following “cropping year” flower buds open, fruit set occurs, followed by harvest in late summer. The majority of wild blueberries are sold to processing plants where most of the berries are individually quickly frozen.

There are approximately 10,000 species of mosses in the Bryophyta or “nonvascular” division of plants (Crum and Anderson, 1981). Mosses have simple leaves covering wiry stems and do not have fruit or seeds (Crum and Anderson, 1981). The life cycle of mosses is also dominated by the gametophyte phase (i.e., exist as haploids), with the sporophyte phase (i.e., the diploid stage) being short in duration and reliant on the gametophyte for survival. The life cycle is initiated with a haploid spore that germinates to form a mat of filaments known as a protonema (Grout, 1903). The protonema subsequently produces the gametophores, which will produce a stem and simple leaves. The sex organs of mosses are produced at the tips and can consist of either the archegonia (female organs) or the antheridia (male organs). Mosses can be either dioicous (both male and female sex organs are borne on different gametophytes) or monoicous (both male and female sex organs are borne on the same gametophytes).

Of particular interest to the wild blueberry industry is the Polytrichum or “hair-cap” genus of mosses (Figure 1). These mosses are the largest and most highly developed terrestrial mosses in northeastern North America, and are characterized with having long hairs growing from a small scale-like body (calyptra proper) at the top of the capsule (Grout, 1903). Polytrichum species are found in moist areas ranging from cosmopolitan areas to coniferous and boreal forests (Silverside, 1998). Known as “hair cap mosses” due to their sporophyte having distinct hairs protruding from the calyptra, these mosses are typically perennial in growth habit, often containing 2 or 3 years of growth, with tall, unbranched stems often reaching 20 to 30 cm in height (Giallombardo, 2001).

FIGURE 1 Presence of common haircap moss (Polytrichum commune) in wild blueberry fields (left) and suppression obtained with autumn applications of Chateau® (a.i., flumioxazin) (upper right side of the right picture) (color figure available online).

Polytrichum commune has been identified as one of the more predominate mosses occurring in wild blueberry fields. Although referred to as nonvascular, Polytrichum commune has fairly clear differentiation of conducting tissue (hydroids) with a well-developed system of tiny tubes for carrying water. Polytrichum commune stems are rigid to erect with lance-shaped, pointed leaves that are approximately 6 to 10 mm long and arranged at right angles on the stem (Giallombardo, 2001). The leaves also have a membranous, sheathing base, and the costa of the leaves is covered in 20 to 55 tiers of photosynthetic lamellae that are 4 to 9 cells high each (Silverside, 1998). Polytrichum commune capsules are horizontally four sided. The capsule contains 64 short, rounded peristome teeth with an expanded central membrane around the capsules mouth. The calyptra has a tuft of hair at the tip and it covers the entire capsule (Ireland, 1982).

Environmental conditions have been ideal for the establishment of this and other mosses in Nova Scotia due to (i) wild blueberry stem heights, stem densities, and canopy wetness durations increasing, (ii) soil organic matter increasing due to the extensive mowing use (vs. burning), and (iii) cool and wet climatic conditions being encountered during the early stages of the growing season for the past 5 years. The subsequent establishment and growth of mosses has increased to levels where they are now observable in the vast majority of wild blueberry fields in the Maritime provinces, and producers have reported situations where suppression of wild blueberry growth and development has occurred resulting in decreased yields. Uncertainty exists on the impact of moss pressures on the wild blueberry and no registered materials for moss suppression are available for blueberry producers to use. Consequently, the objectives of the research were to examine the occurrence, diversity, and intensity of moss pressures and to assess potential moss suppression technologies for use in the wild blueberry industry.

MATERIALS AND METHODS

The moss assessment study consisted of surveying approximately 40 representative commercial wild blueberry fields throughout Nova Scotia between May 13, 2009 and June 30, 2009. At each field, eight 4-m-long, randomly selected, geo-referenced transects were assessed at 25-cm increments for moss type, frequency (% of fields and tangents in which moss is observed), and occurrence (% of point measurements in which various moss species will be observed). At each point measurement, soil moisture, pH, and thatch level was measured. Voucher specimens were collected, identified, and deposited in the NSAC herbaria.

Forty fields were surveyed across Nova Scotia between May 13, 2009 and June 30, 2009. Line transects (8–4 m) were randomly positioned within each field. The area of the field was mapped using a Thales Navigation MobileMapper CE (San Dimas, CA, USA) GPS unit and transects geo-referenced within said area. At 25-cm intervals along each 4-m transect point, samples were taken. Information recorded included the type of vegetation present (blueberry, grass, moss, broadleaf vegetation, lichen, bare soil, or rock); thatch thickness (ruler, in mm); and soil moisture content [Delta-T ML2 ThetaProbe (Cambridge, UK)/Campbell Scientific CS615 Water Content Reflectometer (Logan, UT, USA)]. At 50-cm intervals, soil samples 15 cm deep were collected and amassed into a group-bag for each transect.

Moss competition dynamics were examined in a field experiment established in a commercial field located near Mount Thom, Nova Scotia during the 2008 and 2009 growing seasons. A randomized complete block experimental design was used with a plot size of 2 m × 2 m. The experiment was situated in areas within the field that had approximately 50% of regular wild blueberry stem densities (∼400 stems·m⁻²) and moss cover. The blocking factor consisted of an area within a field, and the treatments consisted of manually removing the moss pressures by 0 (control), 33, 66, and 100%. In each plot, data was collected from two randomly positioned 15 cm × 15 cm quadrats in the vegetative and cropping phases of production consisting of blueberry and moss stem density, stem biomass, and stem height.

Initial field trials examining the suppressive characteristics of various active ingredients against P. commune commenced in 1997 with an examination of spring applied, commercially available moss suppression products (iron sulfate, copper sulfate, and various detergent-based products) (data not reported). With the exception of application of a thermal treatment (i.e., propane burner), none of the treatments suppressed P. commune, resulting in a second set of field trials that were conducted from 2005 to 2009, which included spring (i.e., mid April), pre-emergent applications of the herbicides Velpar® (a.i.: hexazinone), Sinbar® (a.i.: terbacil), Kerb^™ (a.i.: propyzamide), Casoron® (a.i.: dichlobenil), Karmax® (a.i.: diuron), and Chateau® (a.i.: flumioxazin). The only treatment that provided consistent and persistent suppression of P. commune was the Chateau® (data not reported). However, slight phototoxicity effects (i.e., reduction in stem densities) were observed with spring, pre-emergent applications, resulting in the decision to change the application timing to late autumn (i.e., October and November) with the blueberries having been pruned to ground level using a hammer-knife mower two weeks to a month before treatment application.

The influence of autumn applications of Chateau® was investigated with two separate experiments that were conducted from 2007 to 2010. The first experiment consisted of a randomized complete block experimental design with two treatments, a plot size of 4 m × 6 m, and 2-m buffers between plots that was replicated at two field sites consisting of the Wild Blueberry Research Centre (Debert, Nova Scotia) and a commercial field located near Farmington, Nova Scotia. Chateau® applications of 0 (untreated control) and 840 g product∙ha⁻¹ were applied on October 26, 2008, using a Bellspray Inc. (Opelousas, LA, USA), handheld, 2 m, carbon dioxide propelled, boom sprayer with 4 nozzles and using 2-liter sample bottles. The nozzle type consisted of TeeJet Visiflow 8003VS (Wheaton, IL, USA), and a sprayer pressure of 32 PSI (220 kPa) was used. The nozzle discharge rate was 12.5 ml·s⁻¹ and application ground speed was approximately 1.19 m·s⁻¹ at both field sites.

The second experiment was situated in a commercial field in Pigeon Hill, Nova Scotia and consisted of a Chateau® rate trial with application rates consisting of 0, 210, 420, and 840 g product∙ha⁻¹. Treatments were applied on October 21, 2008 using the aforementioned research sprayer. With both experiments, herbicide efficacy data was collected 1 month after treatment application by randomly selecting four 15 cm × 15 cm areas within each plot. Plant phytotoxicty data was collected the following spring (i.e., mid June) due to the treatments being applied when no wild blueberry upright shoots were present. With both experiments, the impact of the treatments on yield potential (including the various yield components) was examined by randomly selecting blueberry stems after fruit set had occurred. This was completed by randomly selected 15 stems from each plot using a line transect, placing the stems samples in plastic bags, placing the bags in a cooler, and bringing the stem samples back to the NSAC for further diagnosis. The parameters examined included stem length, floral nodes, and set fruit. This information was used to measure potential yield in accordance with each treatment.

Prior to the field being mechanically harvested in August, four 1 m × 1 m quadrants were hand raked from each plot using 40 tine commercial blueberry rakes and weighed on a per quadrat basis using a digital balance (Mettler PE 6000, Burlington, Ontario). The specific harvest dates for the experiments consisted of August 19 (moss competition experiment) and August 18 and August 21, 2009 (autumn applied Chateau® experiment).

Data was checked for normality, constant variance, and independence using Minitab (Minitab Release 13.2, Minitab Statistical Software, State College, PA, USA) and SAS (Version 9, SAS Institute, Cary, NC, USA). If necessary, transformations were completed using the Box-Cox option in Minitab. Given that the moss removal treatments were applied on a whole plot basis, ANOVA was completed using the Repeated Measures procedure of SAS. Tukey's Mean Separation procedure was used in examining specific treatment effects.

RESULTS AND DISCUSSION

Of the 40 wild blueberry fields surveyed, mosses were found in every field, but there were 2 fields (Fox Point 837 and Farmington 106) where moss species were not found in any of the line transects. The highest moss pressures were observed in a commercial field near Great Village, Nova Scotia with moss spp. being present at 61.8% of the point measurements examined. Across all commercial fields sampled in the province (n = 40), the mean occurrence of moss was 15.8%. No significant correlation was observed between the presence of moss and soil texture, soil pH, or thatch layer. As expected, a marginally significant (p = 0.054) and weak correlation (0.072) between moss presence and soil moisture level was observed (data not shown). However, upon examining this relationship with the most prevalent moss species (P. commune), this relationship was no longer significant (p = 0.108) (data not reported).

Upon examining the types of moss present in commercial wild blueberry fields, P. commune (common hair cap moss), P. formosum (Juniper hair cap moss), Dicranum flagellare (broom moss), Sphagnum fuscum (common brown sphagnum), and D. scoparium (brook moss) accounted for 92.3, 2.24, 2.17, and 1.06% of the moss species discovered (Table 1). The recent escalation in moss is likely due to the decline in pruning wild blueberry fields over the past 10 years with various thermal technologies (e.g., oil fired burner, use of straw and natural vegetation, or “sickle bar” pruning) as a result of increased fuel costs, permit requirements, fire containment risks, and concerns over particulate emissions. Given the magnitude of P. commune presence in wild blueberry fields, emphasis was subsequently placed on examining the competition dynamics and suppression technologies on this moss species.

TABLE 1 Type and Relative Abundance of Mosses Observed in Wild Blueberry Fields in Nova Scotia during the 2009 Growing Season

Botanical name	Common name	Frequency observed in wild blueberry fields (%)
Polytrichum commune Hedw.	Common hair cap moss	92.3
Polytrichum formosum Hedw.	Juniper hair cap moss	2.24
Dicranum flagellare Hedw.	Broom moss	2.17
Sphagnum fuscum Shim.	Common brown sphagnum	1.06
Dicranum scoparium Hedw.	Brook moss	0.713
Other		1.52

Efforts were made to use wild blueberries that were already under substantial competition from the surrounding moss (wild blueberry stem densities of 400 ± 50 stems∙m⁻² were used) while evaluating the competition dynamics of P. commune with the wild blueberry. The 33, 66, and 100% moss removal treatments had stem densities that were 184, 248, and 361% greater than the untreated control in the vegetative phase of production and 167, 371, and 55% greater than the untreated control in the cropping phase of production (Table 2). In addition, stem heights were also influenced with the 33, 66, and 100% moss removal treatments having blueberry stem heights that were 10.8, 25.0, and 39.2% greater than the untreated control (Table 2). Similarly, the 33, 66, and 100% moss removal treatments had individual blueberry upright stem weights that were 27.7, 45.7, and 68.8% greater than the untreated control (Table 2). Therefore, results from this study clearly indicate the competitive nature of the common haircap moss (P. commune), an apparent lack of an elongation response by the blueberry upright stem in response to this competitive stress, and the resulting negative effects of the hair cap moss on berry yield (Table 2). In addition, the removal of the moss pressures quickly resulted in resumption of stem growth and increased stem densities in areas where the moss pressures had previously persisted.

TABLE 2 P. commune Moss Suppression Influences Blueberry Stem Density, Stem Height, Stem Dry Weight, and Harvestable Berry Yield of Wild Blueberries at a Commercial Field Located Near Mount Thom, Nova Scotia

	Blueberry stem density (stems·m^−2)		Blueberry stem height (cm)
Moss removal level (%)	Vegetative phase of production July 2008	Cropping phase of production June 2009	Vegetative phase of production July 2008	Cropping phase of production June 2009
0	127Bc ^z	107Ac	14.8Ac	15.1Ac
33	361Bb	286Abc	16.4Ab	16.6Abc
66	442Bab	504Ab	18.5Aab	17.9Ab
100	586Ba	701Aa	20.6Aa	21.3Aa
ANOVA results	Sampling time (p = 0.0238) Moss removal (p < 0.0001)		Moss removal (p = 0.0349)
	Blueberry stem weight (dry weight basis: g·stem^−1)
	Vegetative phase of production July 2008	Cropping phase of production June 2009	Harvestable berry yield (fresh weight basis: g berries·m^−2)
0	0.503Ab ^z	0.481Ac	108c
33	0.628Aab	0.614Ab	326b
66	0.692Aab	0.701Ab	447ab
100	0.731Aa	0.812Aa	529a
ANOVA results	Moss removal (p = 0.0016)		Moss removal (p < 0.0001)
^zMean separation was completed using Tukey's mean separation procedure. Capital letters represent significant differences between sampling dates in the vegetative and cropping phase of production. Lowercase letters indicate significant differences due to the level of moss removal that occurred.

Results consistent with the physical removal of the moss competition were obtained with the autumn applied Chateau® (Figure 1). Stem density increases of 51.7 and 54.9% were observed at Debert and Farmington sites, respectively (Table 3). Unlike the physical moss removal trial, increases in stem height were obtained in the autumn applied Chateau® trial with stem heights increasing 38.8 and 22.6% at the Debert and Farmington sites, respectively, presumably as a result of complete competition removal compared to the partial competition removal observed in the moss physical removal experiment (Table 3). However, as was the case with the physical moss removal experiment, the autumn applied Chateau® resulted in set fruit and berry yield increases of 91.7 and 75.6% at the Debert site, and 121 and 61.5% at the Farmington site. This reaffirms that the common hair cap moss (P. commune) was competing with wild blueberry for physical space and resources and needs to be suppressed to minimize negative effects to wild blueberry growth, development, and berry yields.

TABLE 3 Influence of Autumn Applications of Chateau® (a.i., Flumioxazin) on Moss Suppression and Resulting Wild Blueberry Growth and Development

	Visible signs of phytotoxicity to target weed (moss) ^z	Visible signs of phytotoxicity to blueberry ^z	Blueberry stem density (stems·225 cm^−2)	Blueberry stem height (cm)	Number of set berries per stem	Harvestable yield (g·m^−2)
Wild Blueberry Research Centre (Debert)
Control (untreated)	0.2b ^z	0a	8.7b	12.1b	4.8b	283b
Chateau®(Applied at 840 g product∙ha^−1)	9.2a	0a	13.2a	16.8a	9.2a	497a
ANOVA results	Treatment	NS	Treatment	Treatment	Treatment	Treatment
	(p < 0.0001)		(p = 0.0501)	(p = 0.0012)	(p < 0.0001)	(p < 0.0001)
Farmington (commercial field)
Control (untreated)	0.3b	0a	9.1b	16.8a	5.2b	296b
Chateau®(Applied at 840 g product∙ha^−1)	8.9a	0a	14.2a	20.6a	11.5a	478a
ANOVA results	Treatment	NS	Treatment	Treatment	Treatment	Treatment
	(p < 0.0001)		(p = 0.0472)	(p = 0.0338)	(p = 0.0295)	(p < 0.0001)
^zAn injury rating of 0 indicated no injury, values of 4 to 5 indicated severe stunting (i.e., no growth since treatment), values of 6 to 7 indicated stunting and chlorosis, and values of 9 to10 indicated necrosis (i.e., no growth since treatment and tissue death).

Upon attempting to determine the optimum application rate for Chateau®, autumn applied applications rates of 840 and 420 g product∙ha⁻¹ of Chateau® were equally effective in suppressing P. commune in wild blueberry fields with the vast majority of mosses being dead after treatment application (Table 4). The autumn applications of Chateau® also provided no apparent phytotoxic effects to the wild blueberry, which is in sharp contrast to the phytotoxic effects to the wild blueberry being observed with pre-emergent (David Percival, Nova Scotia Agricultural College) and post-emergent applications (David Yarborough, University of Maine) in the vegetative phase of production. Substantial blueberry regrowth was also apparent after applications of 840 and 420 g product∙ha⁻¹ of Chateau® with stem densities being 39.1 and 25.3% greater than the untreated control (Table 4). The low application rate of 210 g product∙ha⁻¹ of Chateau® did not provide adequate moss suppression in this study.

TABLE 4 Influence of Chateau® (a.i., Flumioxazin) Application Rate on Moss Suppression and Resulting Wild Blueberry Growth and Development

	Visible signs of phytotoxicty to target weed (moss) ^z	Visible signs of phytotoxicity to blueberry ^z	Blueberry stem density (stems·225 cm^−2)	Blueberry stem height (cm) ^x
Control (untreated)	0c	0	8.7b	18.1
Chateau®(applied at 210 g product∙ha^−1)	5.1b	0	9.0b	17.9
Chateau®(applied at 420 g product∙ha^−1)	8.4ab	0	10.9ab	18.5
Chateau®(applied at 840 g product∙ha^−1)	9.9a	0	12.1a	18.6
ANOVA results	Treatment	NS	Treatment	NS
	(p < 0.0001)		(p = 0.0382)
^zAn injury rating of 0 indicated no injury, values of 4 to 5 indicated severe stunting (i.e., no growth since treatment), values of 6 to 7 indicated stunting and chlorosis, and values of 9 to10 indicated necrosis (i.e., no growth since treatment and tissue death).
^xA non-significant treatment effect on stem height of blueberries in the vegetative phase of production was present.

CONCLUSIONS

Results from this study indicate that the common haircap moss (P. commune) is becoming a prevalent and significant problem in wild blueberry fields of Nova Scotia. The moss physically competes for space and resources with the wild blueberry, and has the physiological advantage of growing far longer over the course of a field season than the wild blueberry with photosynthesis and plant growth occurring at temperatures below freezing (data not reported). Of all the suppression technologies examined, one application of the herbicide Chateau® (a.i., flumioxazin) was found to provide excellent moss control resulting in recolonization of areas with wild blueberries.

ACKNOWLEDGMENTS

This research was financially supported by the Atlantic Innovation Fund and the Technology Development Program of the Nova Scotia Department of Agriculture. We gratefully thank Bragg Lumber Company, Oxford Frozen Foods Limited, the Wild Blueberry Producers Association of Nova Scotia, and various research assistants and research interns for the contributions made to this project. Mention of a product or trade name does not constitute a guarantee or warrantee of the product by the Nova Scotia Agricultural College nor an endorsement over similar products mentioned.